BSIT-61-MAIN

1BSIT 61 Basics of .NET

Introduction

By the end of this introductory section, you will know

8 New platform - .NET

8 Scope of this book

8 Significance of .NET

8 C# and .NET

8 System Requirements

A New Platform .NET

In the recent years there is an emerging demand and interest among the software designers to implementthe applications independent of the hardware, operating system and language. Microsoft made a successfuleffort to provide a platform for advanced complex applications to be developed easily. Microsoft .NETframework provides an efficient way to develop softwares in any platform and to use any language. C#is a new language released with .NET.

Scope

This scope of this book provides basics of .NET platform. All the chapters in this book can be dividedinto three sections.

BSIT 61 Basics of .NET 1

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In first section you will study .NET concepts and its architecture. Chapter 1 and 2 belong to thissection. The Chapter 1 is very important as it forms the clear foundation about the subject and it helps inunderstanding future chapters. Chapter 2 gives architectural details about .NET.

In Second section, students will learn a new programming language C#. This language is used throughout this book to understand the concepts of .NET via C# examples. Chapters 3, 4, 5 and 6 come in secondsection. Chapter 3 gives introduction about this language. Chapter 4 and 5 gives the C# languagespecifications. The 6th chapter includes some of the advanced topics of C#.

The third section explores some of the important .NET technologies. The ADO.NET for databaseprogramming, internet technologies like web forms, web services, ASP.NET and the .NET remotingtechnique, all are covered in this section.

Significance of .NET

The Microsoft is well known for its operating system for home PC. From Windows 3.1 developed in1992 to today’s Windows XP, Microsoft has made many advances in its technologies. With the developmenttowards new technology it has to maintain backward compatibility with the existing technologies. As theresult of this huge number of new functions are added to the set of existing Windows API’s. (WindowsAPI are set of basic functions provided by operating system. API functions can directly communicatewith hardware).

Backward compatibility is the strength of the Windows but at the same time backward compatibilityhas one major disadvantage. Every time the new technology is introduced, the new sets of features areadded to Windows API. The existing technology is modified keeping backward compatibility in mind. Thismakes the code and the design much more complex. Again and again upgrading technologies makes thecode so complex that after few years it becomes very hard to write new technology on existing one.

To overcome these complexities there has to be one new fresh start. This fresh start is what .NET isall about. .NET is a new framework developed with new set of API. C# is a new language designed fromscratch with .NET and for .NET platform. .NET platform supports object-oriented programming. The C#is a purely object-oriented language.

The .NET framework has Visual Studio.Net which is the upgradation of Visual Studio. In VisualStudio Visual Basic (VB) was very well known for its simplicity and large number of controls but did nothave good debugging feature. Whereas the VC++ had well built debugging feature, but did not had thesimplicity and vast controls as in VB. Similarly there were many facts in which one technology was goodin one and week at other. The Visual Studio.Net has overcome all these facts. Now VC++.Net has easily

Introduction


addable controls and VB.Net has good debugging features.

The important thing to note is that even though the .NET is a fresh start it supports backwardcompatibility. It is capable of running applications developed in Visual Studio on Visual Studio.Net.

C#

C# (pronounced “C Sharp”) is a simple, modern, object oriented, and type-safe programming language.It is immediately familiar to C and C++ programmers. C# combines the high productivity of Rapid

Application Development (RAD) languages and the raw power of C++. Here are some of the pointsabout C#.

l C# is a new language with .NET Framework. It’s a purely object-oriented language and developed

from scratch with .NET to make use of all feature of .NET.

l C# is a simple but powerful programming language intended for writing enterprise applications.

l The C# language is an evolution of C and C++. It uses many C++ features in the areas ofstatements, expressions, and operators.

l C# introduces considerable improvement and innovations in areas such as type safety, versioning,

events, and garbage collection.

l C# provides access to the common API styles, COM, Automation, and C-style APIs. It alsosupports unsafe mode, where you can use pointers to manipulate memory that is not under the

control of the garbage collector.

System Requirements

To build and run your C# programs, you need

1 Windows 2000, XP, NT or Me

1 IE 5.5

1 Microsoft .NET SDK (Beta 1)

1 Visual Studio .NET (optional - available for MSDN Universal Subscribers)

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1 C# IDE – Sharp Develop (optional).

The .NET SDK can be freely downloaded from

http://msdn.microsoft.com/netframeworkIt’s an 80MB download. The C# compiler (csc.exe) currently ships with the .NET beta.

The C# IDE is available from

http://www.icsharpcode.net/OpenSource/SD/Download/Default.aspx

Introduction


Chapter 1

.NET Overview

By the end of this introductory section, you will know

8 Have a overview about .Net Framework

8 Know what all Languages and Technologies are supported by .NET

8 Advantages of .NET

Before we actually start with the subject, we have to make ourselves clear with the following questions.

1 Why should we study the “Basics of .NET”?

1 What is the need of .NET?

1 What is the pre-requisite for this subject?

1 What should be the student’s role?

.NET is a new Framework from Microsoft. But what is this Framework? And what is inside it?

.NET Framework comprises of programming methodologies (Visual Studio.NET and Mixed languageprogramming), Platform technologies (ADO.NET, Windows Form) and Code Execution environment. Allthese things are comprised together into a framework, to provide object-oriented development platform.

Let us take the above questions one by one. So why do we need to study this subject “Basics of.NET”? So far in your course you have studied programming languages like C, C++ and Java. If youcompare all these languages you notice that the syntax of all languages is some what same. After youstudied C programming, the efforts required to study C++ programming becomes less, isn’t it? And when


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you started Java after C++, the Java language also looked easy to understand. But .NET is a ModernSoftware Technology. It is not just the programming language to learn, but a bunch of technology. It istime to learn the current generation software practice, using .NET.

.NET has been built up with the aim to give provide modern software technology. This subject will helpyou to learn new programming methodologies and new technologies. The .NET framework has been builtup so well that just knowing how it’s been designed is very interesting.

Pre-requisite for this subject is knowledge about either C++ or Java, because the idea about the ObjectOriented Programming (OOP) would make understanding of .NET concepts easy. Students should nothave to be an expert in OOP, just the idea of it will do. As the .NET Framework is built on complete objectoriented methodology, and it supports OOP, the knowledge of OOP is essential for the students. Toexplore the .NET and its features, we require a language. C# would be a best choice, because C# wasdesigned on .NET Framework. C# has a capability to make best use of all .NET services. It resemblesC++ and Java syntactically, so students who know anyone of these programming languages would learnfast.

Any subject will be interesting only if the students are regularly exercised with it. In this book at theend of each chapter, there are set of questionnaires. The students must solve all these questionnaires,after studying each chapter. These questionnaires are designed to help students to analyze themselvesand understand the chapter better.

1.1 .NET FRAMEWORK OVERVIEW

From the above discussion, you can broadly make out that the .NET Framework is an environment forthe developers. It mainly comprised of programming methodology and technologies. To understand the.NET Framework, we should explore three major areas

l Programming Methodologies

l Platform Technologies

l Code Execution

There is two ways of learning .NET. One is ‘Breadth wise learning’ and the other is ‘Depth wiselearning’. In Breadth wise learning, we will explore all the features and services of .NET. We will notanalyze each area or services in depth; we just understand what is the role of each area. In “Depth wiselearning”, we analyze each area, its role and its services. This type of learning is done by professionalprogrammers, when they start programming in a particular area. Generally “Depth wise learning” comesafter “Breadth wise learning”. This book provides only “Breadth wise learning”. This book tries to covermost important areas of .NET, so the students are exposed to the new world of software development.

Chapter 1 - .NET Overview


Programming Methodology

On the Programming Methodology side, an interesting thing about .NET is that it allows for mixed-language programming. By designing from the ground up a specification that is common to all the languagesthat work in .NET Framework, by designing a type system that all those languages support, and byspecifically designing an intermediate language that all those languages compile into; before they compilein native code. The designers of .NET were able to build a system where the programmer can freely mixmodules of the program between one language and another. For example, we might write our userinterface in C#; we might write some low-level computational code in C++. We might write some otherpart in Visual Basic. It just does not really matter in a .NET framework. This technology is a publiclystated and internationally approved standard by the ECMA Group.

C# is simply another programming language that now has a standard definition; it can be implementedby any manufacturer on any platform. It is the language that was designed specifically to be the bestlanguage to use with the .NET platform.

Platform Technologies

In Platform technologies, we will mainly go through – ADO.NET, Internet technologies and Userinterface designing. The following paragraphs talks about these topics.

Let us move to Platform Technologies, a little bit. In .NET framework we have put together platformswithin the platform. ‘ADO.NET’ is the technology that is used for accessing databases. .NET has improvedthat kind of programming dramatically from an ease-of-use standpoint, through some features. There isan entity called a strongly typed database. We will see how that works in later chapter, when we get todatabase programming. The net effect of ADO.NET for the programmer has greatly simplified andenhanced capability of programming with databases. It is a really nice technology. .NET also uses adisconnected model of database programming where we have a database sitting out on a database server.What we do is acquire the data from the database that we want into an end-memory dataset, and then weprogram against that.

Moving into the ‘Internet world’, this was certainly one of the keystones of the development of .NET,as we can tell from the name. The particular part of the technology that deals with the Internet is calledASP.NET. There are two or three things that we have to talk about here. In the first place, there issomething called Web Forms. The idea of developing software for the Internet can be tricky. It can beespecially tricky if we are trying to have a reasonable amount of programming logic sitting behind a Webpage. The Web Forms brings visual design to Web page, just like with an ordinary Windows program. Wecan write web designing code in any language that we want to. We are not limited to some scriptinglanguage. If we want to program our Web page in C#, we are allowed to do that. We can again mix thelanguages; we can do whatever we want. It is a very interesting new way of writing Web applications.

The idea here is to look at the other side of the Internet. Certainly a lot of people believe that the partof the Internet that is going to ultimately prove to be the most valuable is not browsing the Web in the

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normal way that a user does, but computer-to-computer communication. That seems to be a great futurefor business-to-business type applications and a great many other server-software development activitiesare going to depend in the future on Web Services. There is a very strong support for web services inMicrosoft .NET. Not only it is strong, it is simplified from the standpoint of the programmer. It is easy towrite software that runs on one machine but is called by a program on another machine and sends itsresults back to other machine. Web services are one of the key components that we will talk about in laterchapter. .NET Remoting is sort of Web services, its implementation lets us think about how one computercan interact with and access objects that are stored at another computer, without having to worry as aprogrammer about the low-level protocol details. It is a more powerful version of Web services.

Another place where .NET has innovated is in User ‘Interface Design’. It has started with, in theworld of Visual Basic. In C++ we struggle with hacking code to position our buttons and our text boxes,whereas the Visual Basic people were just dragging them on the screen and putting them where theywanted them. In .NET we can do that in any language. That’s the beauty of the common-languageapproach. It is the beauty of the tools that Microsoft has built, that works with those languages. TheWindows programs that run under .NET which are designed visually are called as WinForms.

There is another interesting concept called Data Binding. We often put fairly complicated controls onthe surface of our application screen. For example, we want to put up a table that is a grid, which issupposed to display some data that comes into a dataset out of a SQL Server. So, how do we get it fromour end memory (say SQL server) dataset into the user interface widget that is supposed to display it insome sort of list box or grid? .NET supports a concept called data binding that lets that happen completelyautomatically. The data source for this grid is this particular dataset, and that is the end of it. If we changethe dataset, the grid updates automatically. If we change the grid programmatically, it updates into thedataset, and then we can decide whether to commit those changes to the database. It is a very nice andvery powerful concept.

Code Execution

The interesting thing about code execution on .NET framework is, when we hear about .NET, wethink, that it is particular to Intel-based computers. But it is certainly not. The standardized commonlanguage infrastructure is completely architecture-neutral. The whole purpose of making it standard andputting it in the public domain was so that that infrastructure could be implemented on any platformwhatsoever. The whole idea is that we are neutral in terms of the architecture.

Another interesting idea in .NET, of course, is the notion of just-in-time compiling. In the .NETplatform, all the .NET languages get compiled into the Microsoft Intermediate Language or simply calledas intermediate language. This intermediate language gets compiled by just in time compiler, to the nativemachine code. Just-in-time compiler has another great feature; it compiles the part of code as and whenrequired. One of the nice features that all modern languages exhibit is garbage collection. With thisgarbage collector, programmer does not have to worry about freeing memory that has been allocated forsome purpose. It is automatically done. Naturally, that is a great burden lifted off the programmer’s



shoulders, as opposed to certain other languages, say in the C family of languages where we are constantlyfighting that problem. Certainly, one of the goals was to have type safety. That is one of the hallmarks ofC# and the other .NET languages. It is obviously the modern way to go about programming.

The .NET is a technology that was designed for and really born out of the idea of how can we makeit easier to write software? How can we make it easier to write software for Windows, how can wemake it easier to write software that works through the Internet, how can we take some of the developmenttime that people are spending on low-level details, and simply do them automatically? .NET answers allthe above questions and lets the programmer get on with the real job. That is what .NET is about. Itintroduces the language C#. It is a language that has become very favorably inclined to developersnowadays. Certainly it is language of choice these days in any software that they are going to write. C#is the newest major language that is been designed. The people, who built software in all the otherlanguages, now know what works; they know what is frustrating. They know what is powerful; theyknow what is not needed. The designers of .NET tried to make the best decisions that they thought theypossibly could in putting together a new language that would be tailored to this framework but serve theneeds of a programmer. They did an amazingly good job at it.

1.2 LANGUAGES AND TECHNOLOGIES

The .Net framework has integrated few main languages and other existing technologies within it. Letus have a brief look at them.

C#

C# is a new language developed with .NET and for .NET platform. It is a new language, which iscapable of using all services provided by Dot Net platform. C# compiler always produces managed codeafter compilation.

C# language is significant because of two important facts

1. It is highly compatible with the .Net Runtime. It is designed to run on .Net environment.

2. It is a modern object-oriented programming language. The word ‘modern’ specifies some newtechniques are used in designing this object-oriented language.

C++

Even with new and more powerful language C#, .Net also supports C++ because of backwardcompatibility. Many features are added to the C++ to make it stronger on .Net framework. To run a C++code on .Net framework, we need to include below line at the beginning of the code.

#using <mscorlib.dll>

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The compiled code will be managed code. But if the code is unsafe using low level pointer manipulation,then the C++ compiled code dose not pass CLR memory safety checks.

J++

No updations are made to this language. It is supported on .Net only for backward compatibility. Thereis much similarity between the J++ and C# syntax, So a tool which converts the J++ code to C# code isprovided by .NET. Using this tool we can use convert J++ application to C# and use the facilities providedto C# language.

VB.NET

Visual Basic is been upgraded to Visual Basic.Net (VB.NET) on .Net Framework. Many new featuresand many new controls are added. Good debugging facility is provided.

The compiled code of VB.NET is intermediate code as in the case of C#. The VB applications alsowork on VB.NET as the backward compatibility does exist.

ASP.NET

ASP is upgraded to ASP.NET on .Net Framework. The coding can be done directly in any of C#,VB.NET or JScript.NET. The code is compiled into classes which respond to the web requests. Becauseof backward compatibility the ASP code still continues to run on this new platform.

Scripting Languages

JScript is now upgraded to JScript.NET. The JScript.NET is used to code ASP.NET applications. Asbefore now the Jscript is not interpreted, it is now compiled to intermediate code.

ADO/OLE DB

ADO.NET has been added new features like communicating with data sources which is made easy.ADO.NET is now the subset of .NET Base Classes.

COM and COM+

The COM+ remains as an important tool in .NET. COM works on .NET because of backwardcompatibility. Now on .NET Framework, calling and managing the components has become easy because.NET incorporates the COM interoperability feature.

1.3 ADVANTAGES OF .NET

The .NET Framework offers a number of advantages to developers. The following are few importantamong them.



Consistent Programming Model

Different programming languages have different approaches for doing a task. For example, accessingdata with a VB application and a VC++ application is totally different. A developer has to know bothdifferent techniques to do the task.

In case of .NET Environment, for the same example, displaying data from database in a grid accessingdata with a VB.NET and a C# is very similar except slight syntactical differences. Both the programs usethe System.Data namespace, establish a connection with the database and run a query and displays thedata on a data grid. The .NET there is a unified means of accomplishing the same task by using the .NETClass Library, a key component of the .NET Framework.

The .NET Class Library provides the functionality to all .NET languages resulting in a consistentobject model regardless of the programming language used by the developer.

Language Independence

Language Independence means the developer has the independence to code one module of an applicationin one language and other module of same application in other language. This language interoperabilitycan help in code reuse and improve the efficiency of the development process.

No versioning Problem - Easy Application Deployment and Maintenance

The .NET Framework makes deployment of applications easy. Commonly, to install an application allwe need to do is, copy the application along with the components it requires into a directory on thecomputer. The .NET handles the details of locating and loading the components an application needs,even if several versions of the same application exist on the computer. The .NET ensures that all thecomponents the application depends on are available on the computer before the application begins to run.

Improved Security

The .NET Framework provides several mechanisms for protecting resources and code from unauthorizedusers:

l ASP.NET Web Application Security provides a way to control access to a web site by comparingauthenticated permissions with File System permissions for proper authorization.

l Code access security uses permissions to control the code accessing protected resources andoperations. The computer systems are protected from suspicious mobile code and provide away to run mobile code to safely.

l Role-based security provides information needed to make decisions about user’s permissions.

Support for Web Services

Web services are remote databases and programs, which access other computers to read the data

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files. With the advent of .NET technology, web services provide many built in Base Class library facilitieswhich open up a whole new world of information for users. Web services can provide everything frombasic text news information to vital database or application information

Dynamic Web

Content that changes with the user and user preferences is an example of dynamic webcontent. Dynamic web content is easier to create with .NET. ASP.NET and Visual Studio.NET allowdevelopers to create dynamic web much easier than IIS and ASP technologies.

Visual Studio.NET

Visual Studio.NET is the Microsoft application and interface for programming in .NET. Visual Studio.NET provides all the programming advantages mentioned so far. This development environment hasextensive set of ready to use controls, good debugging facilities, easy and simple programming featuresand vast set of .NET Base Classes.

SUMMARY

Microsoft has developed .NET Framework. .NET Framework is comprised of programmingmethodologies like Visual Studio.NET and Mixed language programming, Platform technologies likeADO.NET, Windows Form, etc and Code Execution environment. We have briefly explored .NETframework in this chapter. The .Net framework has integrated few main languages and other existingtechnologies within it. They are C, C++, J++, VB.NET, ASP.NET, Scripting Languages- JScript.NET,ADO.NET, COM and COM+.

The advantages of .NET Framework are:

l Provides Consistent Programming Model

l Has Language Independence

l No versioning Problem - Easy Application Deployment and Maintenance

l Improved Security

l Support for Web Services

l Dynamic Web facilities

l Full fledged Visual Studio.NET

QUESTIONS

1. What is .NET Framework?



2. What does .NET Framework comprised off?

3. Write a note on

a. Programming Methodologies

b. Platform Technologies

c. Code Execution

4. Which are the Platform technologies supported by .NET framework?

5. List out the advantages of .NET framework.

6. What is backward compatibility? (Backward compatibility – self study topic)

7. Does .NET platform support backward compatibility? Explain.

14 Chapter 2 - Components of .NET Framework

Chapter 2

Components of .NET Framework

In this chapter, you will

8 Learn .NET Architecture and its Component

8 Study each component like Common Language Runtime, Assemblies,Application Domains, Common Type System, and Metadata in detail

8 Understand Common Language Specifications

8 Briefly explore .NET Framework Class Library

2.1 .NET FRAMEWORK

In the previous chapter we had an overview about the .NET Framework. In this section we will seedifferent layers of .NET framework. The below figure 1.1 will help us to understand the design of theframework better.

Down in the bottom of the figure 1.1, we have operating system not only Windows on which .NETworks on, there are also implementations that work under Linux. .NET Framework tries to provide anabstraction between application and operation system services. The .NET common language runtimeknows how to get those services from the particular operating system. Common language runtime isrunning on top of operating systems. It is the execution engine in which a .NET programs execute. It alsoprovides memory services and garbage collection.

Chapter 2 - Components of .NET Framework14


Figure 1.1 : Layers of .NET Framework

Sitting on top of common language runtime is a very large class library. That is the part of .NET whichprovides all those different platforms technologies that we were talking about in previous chapter. LikeADO.NET to access databases or ASP.NET to write Internet-enabled software. All those servicesreside in what we call collectively as Framework Base Class Library. Sitting on top of all, is ultimatelysome programming languages. As mentioned earlier that .NET supports language interoperability and toimplement it, Microsoft has created a common language specification. These specifications are rules bywhich any .NET language has to play. If the application is implemented based on these rules then it canquite freely interoperate with any of the other .NET languages.

Some of the major functions that the common language runtime provides are shown in below figure1.2.

Figure 1.2 : Common Language Runtime and its major functionalities

Common Language Runtime

Framework Base Class Library

Windows LINUX

Common Language Specification

VB.NET C++ C# Scripting Languages

ASP.NET

Microsoft Visual Studio .NET

Common Language Runtime

• Execution Environment

• Memory Management

• Garbage Collection

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It is, as mentioned, the execution environment. It is the place where code executes. That means thatthe common language runtime is managing or denying memory access. It is the part of the Frameworkthat does memory management. When new objects are created, they are created on the managed heap,and that is taken care of by the common language runtime. It garbage collects those objects which are nolonger needed. Garbage collection is completely automatic.

Another interesting part of all this, part of the common language runtime, is what we call the CommonType System. The reason it is interesting is the following; every object in a .NET program inherits from acommon superclass called Object. As shown in the below figure 1.3. There are two main types; valuetypes and reference types. This is a way that .NET languages differ a little bit from some other programminglanguages.

Figure 1.3 : Common Type System

Value types in .NET are what you normally think of as the primitive types in a programming language.ints, doubles, strings, all those sorts of things. Here ints, doubles and string all are objects and they havemethods. It means the integer 2 (here 2 is a object) has a method called tostring, which you can call to getback the string version of the integer 2. Here it is a unified type system where value types, referencetypes, whatever they are, they are all objects. They all share a certain common level of behavior. Valuetypes are allocated on the stack. So few questions to be cleared here are:

Being a value type, what happens when you assign one to another?

The value gets copied.

How are they de-allocated?

If they’re allocated on the stack, they’re obviously de-allocated when that block that is usingthat stack exits.

Chapter 2 - Components of .NET Framework


Can we have user-defined types?

Yes we can. We have the notion of structs in .NET languages and those are user-definedvalue types.

Now a few word about the reference types. The reference types are objects. They are what wenormally think about in object-oriented programming environments like classes and arrays. They areallocated on the managed heap, not on the stack. An reference type assignment, just copies the reference.If we have some type of object, says a customer, and we assign customer1 to customer2, we have notcopied the entire object in all of its state. We have simply copied the reference. Reference types aregarbage-collected. They are never explicitly freed. The common language runtime takes care of that.

About Framework class library the main thing to say is, it is big. There is an amazing wealth of toolswithin it. They are divided into namespaces. System namespace is the highest level; it contains a fewdefinitions and also contains some of the other namespaces.

Figure 1.4 : Framework Class Library and its major library classes

The Collections namespace contains the definition of collection types like stacks, queues, and hashtables, an array list. All the things you would expect in any modern programming language are in it. Thereis a drawing library that gives you access to a very rich set of tools for doing drawing and graphics I/O.The Data namespace contains the ADO.NET database tools. Windows.Forms is the part of the librarythat deals with writing the User Interface for Windows applications. Web.UI deals with that for Web-based applications and Web.services. The Framework class library is extensive and very large.

Here we will see back at the big picture in figure 1.1 again. We have got operating systems. We havegot a common language runtime looking over our code. Large framework base class library above commonlanguage runtime. On top of all, we have got program languages, and letting us get an access to all of itis Visual Studio .NET.

Let us talk a little bit more about how languages work. A common language specification layer underneath

Framework Class Library

_____________________

• System

• System.Collections

• System.Drawing

• System.IO

• System.Data

• System.Windows.Forms

• System.Web.UI

• System.Web.Services • �

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all languages, are in some sense bounded by the same rules. They are all using the same basic definitionsfor the primitive types. The way it works is shown here in below figure 1.5. This figure shows interestingpart of the design of the .NET approach.

Figure 1.5 : Common Language Specification support language

interoperability through intermediate language

Naturally, if we are writing application in C#, we need a C# compiler. If we are writing in Visual Basic,we need a Visual Basic compiler. Even for C++, we need a C++ compiler. The approach taken here isthat all of those compilers compile into this same intermediate language. The intermediate language isthen compiled by Just-In-Time compiler to native machine code. So regardless of what language we writeour code in, it all compiles into same intermediate language. That language is the same no matter what thesource code was.

Once we reach that stage, there is no way to even know or care what the original source codelanguage was, it is all just compiled into the intermediate code.

The designers of .NET had in their mind from the very beginning the idea that they were going to usea just-in-time compiler. The idea is, that just-in-time compiler only needs to understand one language, notall of them. It only needs to understand the intermediate language. It compiles it into native code andnaturally, that does not take place until run time. That’s the .NET approach.

We compile it into intermediate code. That is the result of the compilation process. It sits on themachine and when the user finally runs that code, it is compiled as needed into native code on the fly.That’s the just-in-time part. That process is obviously completely automatic and independent of how theprogram is coded. Once we have compiled it into intermediate language, it’s done. The common languageruntime takes care of the rest. The reason for doing this, of course, is performance. No matter in which

C# Code

Visual Basic

Code

C++ Code

C++

Compiler

Visual Basic

Compiler

C# Compiler

Intermediate

Language

JIT Compiler

Native Code



.NET language we are writing in, when it comes time to running the code, it is running as native compilecode, and it runs very, very fast at many native-code speeds. That was the goal of this approach.

.NET gives a managed execution environment. We get automatic memory management. We getgarbage collection. We get lots and lots of libraries that allow us to write very rich programs in a veryshort amount of time. We also get a set of application programming interfaces that enable the writing ofInternet-based software. That is just one of the cornerstones of .NET, and it is one of the things that makeprogramming fun.

Intermediate language gives a way to achieve language interoperability. Just think about it. If all thelanguages compile into the same intermediate language, then why shouldn’t code from one be able to callup code from another? After all, once we are at that stage, there is no difference. That is exactly the wayit works. We can write a class in C#. We can derive a subclass from it in Visual Basic. One of thoseobjects might throw an exception. We can catch that exception in some other part of the code that iswritten in yet another language. It means we can tailor each part of a multi-module program in such a waythat we use the language that is most appropriate for it. This is what the designers were shooting at.

We also get from .NET Visual Studio, a rapid development environment that is absolutely perfect.Developers now do not need to keep fighting with the environment; they can just think about the code thatthey are writing. We also get a very interesting new language, C#. We will be moving into that topic C#,in next chapter. It is a cutting-edge, state-of-the-art language that exhibits all the best things that wecurrently know about designing a higher-level language.

2.2 .NET ARCHITECTURE AND ITS COMPONENT

The .NET Framework is a new computing platform that simplifies application development in thehighly distributed environment of the Internet. This section gives technical description about .NETarchitecture.

The Objectives of .NET Framework are:

l To provide an object-oriented programming environment whether object code is stored andexecuted locally, or executed remotely.

l To provide a code-execution environment that minimizes software deployment and versioningconflicts.

l To provide a code-execution environment that guarantees safe execution of code, includingcode created by an unknown or semi-trusted third party.

l To provide a code-execution environment that eliminates the performance problems of scriptedor interpreted environments.

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l To make the developer experience consistent across widely varying types of applications, suchas Windows-based applications and Web-based applications.

l To build all communication on industry standards to ensure that code based on the .NETFramework can integrate with any other code.

The .Net Runtime sits between the Windows operating system and the application programs built on.Net technologies. The below figure demonstrates that the .Net application programs cannot directlycommunicate with the operating system. The .Net runtime uses the .NET base classes to communicatewith operating system.

Figure 1.6 : .Net Runtime and Base class library lies between the application programs and operating system

We can classify the programming on Microsoft Windows platform into two types

1. Windows Programming

2. .NET Programming

In Windows Programming the application programs call windows API function directly. The applicationsrun in the windows environment i.e. operating system itself. These types of applications are calledunmanaged or unsafe applications.

In .NET Programming the application programs call .Net Base Class library functions which willcommunicate with operating system. The applications run in .Net Runtime environment. These types ofapplications are called as managed or safe applications. The .Net Runtime starts code execution, managesthreads, provides services, manages memory etc. The detailed description is provided in next section. The.Net Base classes are fully object-oriented. It provides all functionalities of traditional windows API alongwith functionalities in new areas like accessing database, internet connections and web services.

Some definitions of .Net components and other terminologies are given below. These terms or definitionshave to be understood well before moving on to the detailed study about .NET.

Windows Operating System

Windows API

.NET Runtime & Base Classes

.NET Application Programs

.NET Framework



l Common Language Runtime (CLR)

This is also known as .NET Runtime. The code management is a fundamental principle of theruntime. The responsibility of runtime is to load the code, run the code and provide all kinds ofservices. The services provided by .NET Runtime are as memory management, threadmanagement, remoting, strict type safety, ensure code security and robustness.

l Managed Code

Managed code is one which is designed to run on .Net environment. The code which runs inwindows environment is unmanaged code.

l Intermediate Language (IL)

This is also called as Microsoft Intermediate Language (MSIL). The intermediate language isanalogous to the byte code of Java. The significant difference is that the byte code in interpretedwhile the IL is compiled by JIT compilation to native machine code.

Figure 1.7 : .NET programming languages compilation process

The IL code is not the machine code. The .Net Runtime calls the Just-in-Time (JIT) compiler toget native machine code from IL code. This feature makes the .NET platform independent.

l Common Type System (CTS)

This is a standardized agreed set of basic data types. This system provides a way for languageinteroperability. Language Interoperability means that a object implemented in one language cancall a object implemented in another language. In more general way you can say that a applicationcan be developed in two or more languages supported by .Net framework. To make use oflanguage interoperability feature, the developers have to follow CTS.

Compiler

.NET

Source Code

Intermediate

Language (IL)

JIT Compiler

Native Machine Code

IL Code

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l .NET Base Classes

.NET Base Classes is a library comprising of extensive set of functions for all services supportedby the framework. This vast collection has well written code for almost all tasks on all servicesof .Net framework. The services can be windows creation/displaying or form handling, internetor web services, database accessing or file handling.

l Assemblies

An Assembly is the unit in which compiled managed code is stored. An Assembly contains ILand metadata. Metadata gives details of the assembly, properties and methods stored in it,security information etc.

l Common Language Specification (CLS)

The set of rules of basic language features has been defined to enhance and ensure languageinteroperability is called the Common Language Specification (CLS). The CLS rules define asubset of the CTS.

l Reflection

The process of obtaining information about assemblies and the types defined within them asmetadata at runtime.

l Just-in-Time (JIT) Compilation

The compilation converts IL into its native machine code. The name Just-in-Time is because itcompiles portion of code as and when required at run time.

l Manifest

The area of assembly where metadata is stored is called as manifest.

l Application Domain

A boundary that the common language runtime establishes around objects created within thesame application is by means of Application Domain. Application domain allows different codeto run in the same process space.

l Garbage Collection

The Garbage Collector frees the application from the responsibility of freeing memory when nolonger required. CLR calls Garbage collector to handle memory efficiently.

.NET is tiered and modular. Each tier of the .NET Framework is a layer of abstraction. .NETlanguages are the top tier and the most abstracted level. The Common Language Runtime (CLR) is the



bottom tier, the least abstracted, and closest to the native environment. This is important since the CLRworks closely with the operating environment to manage .NET applications.

The .NET Framework is partitioned into modules, each with its own distinct responsibility. The highertiers request services only from the lower tiers, so .NET is hierarchal. The modified architectural layoutof the .NET Framework is illustrated in figure 1.8 below.

Figure 1.8 : Modified architectural layout of .NET Framework

The .NET Framework is a managed environment. The CLR monitors the execution of .NET applicationsand provides required services. It manages memory, handles exceptions, ensures security, and muchmore.

Language interoperability is one goal of .NET. .NET languages share a Common Language Specification(CLS), Common Type System (CTS) and Framework Base Class Library (FCL). Web Services, ADO.NET,

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Windows or console applications and Remoting execute on CLR. In .NET, the programming language likeC#, VB.NET, or JScript.NET has similar experience except little differences. .NET abstracts lower-levelservices, while retaining most of their flexibility.

Assemblies, Application domains and metadata are brought to CLR environment before they areexecuted. Once they are brought to the execution environment, CLR takes the responsibility of managingand executing it. More details are provided in the following topics.

The important components of .NET Framework are:

l Common Language Runtime

l Assemblies

l Application Domains

l Common Type System

l Metadata and Self-Describing Components

l Common Language Specifications

l .NET Framework Class Library

Each of the above components are described in detail in the following sections

2.3 COMMON LANGUAGE RUNTIME

The .NET Framework provides a run-time environment called the Common Language Runtime, whichmanages the execution of code and provides essential services.

Lets go through the functionalities of CLR and how does it accomplishes it.

To enable the runtime to provide services to managed code, language compilers must emit metadatathat describes the types, members, and references in your code. Metadata is stored with the compiledcode. Every loadable file contains metadata called as portable executable (PE). The runtime uses metadatato locate and load classes, lay out instances in memory, resolve method invocations, generate native code,enforce security, and set run-time context boundaries.

The runtime automatically handles object layout and manages references to objects, releasing themwhen they are no longer being used. Automatic memory management eliminates memory leaks as wellas some other common programming errors.

The CLR makes it easy to design components and applications whose objects interact across languages.Objects written in different languages can communicate with each other, and their behaviors can be



tightly integrated. This cross-language integration or language interoperability is possible because languagecompilers and tools that target the runtime use a CTS defined by the runtime, and they follow the runtime’srules for defining new types, as well as for creating, using, persisting, and binding to types.

The runtime uses metadata information to ensure that your component or application has the specifiedversions of everything it needs, which makes your code less likely to break due to some dependency.Registration information and state data are no longer stored in the registry where they can be difficult toestablish and maintain. Rather, information about the types and their dependencies is stored with the codeas metadata.

The managed execution process includes the following steps:

l Choosing an appropriate language compiler.

l Compiling code to Microsoft intermediate language (MSIL or simply IL). Compiling translatessource code into IL and generates the required metadata.

l Compiling IL to native code. At execution time, a just-in-time (JIT) compiler translates the ILinto native machine code. During this compilation, code must pass a verification process thatexamines the IL and metadata to find out whether the code can be determined to be type safe.

l Executing code. The CLR provides the environment that enables execution to take place aswell as a variety of services that can be used during execution.

NOTE: In the above paragraphs some words are in italic. Those paragraphs are based on those wordor concepts.

2.4 ASSEMBLIES

Assembly is a basic element of packaging in .NET. An assembly consists of IL code, metadata thatdescribes what is in the assembly, and any other files or information that the application needs to run, suchas graphics and sound files.

An assembly performs the following functions:

l It contains code that the CLR executes. Assembly contains IL code plus the manifest in aportable executable (PE) file will be executed by CLR. Note that each assembly can have onlyone entry point (i.e., DllMain, WinMain, or Main).

l An assembly is the unit at which permissions are requested and granted. Hence it forms asecurity boundary.

l It forms a type boundary. Every assembly has a unique name and the type’s within those assembliesincludes the name of that assembly. Hence every type has unique name or unique boundary.

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l The assembly’s manifest contains assembly metadata that is used by CLR for resolving typesand satisfying resource requests.

l It forms a version boundary. The assembly is the smallest versionable unit in the CLR. All typesand resources in the same assembly are versioned as a unit. The assembly’s manifest describesthe version.

l It forms a deployment unit. When an application starts, only the assemblies that the applicationinitially calls must be present. Other assemblies, such as localization resources or assembliescontaining utility classes, can be retrieved whenever they are called. This allows applications tobe kept simple and thin at first.

Assemblies can be static or dynamic. Static assemblies can include .NET types (interfaces and classes),as well as required resources for the assembly (bitmaps, JPEG files, resource files, and so on). Staticassemblies are stored on disk in PE files. Dynamic assemblies are one which run directly from memoryand are not saved to disk before execution. They can be saved disk after they have executed.

2.5 APPLICATION DOMAINS

Application domains provide a secure and versatile unit of processing that the CLR can use toprovide isolation between applications. This isolation is necessary to ensure that code running in oneapplication cannot adversely affect other unrelated applications. Application domains are typically createdby runtime hosts, which are responsible for bootstrapping the CLR before an application is run.

Figure 1.9 : Separate process for each application in traditional execution environment

Portion of physical memory or disk space

Portion of physical memory or disk space

Process

1

Process

2

Physical Memory



Historically in traditional case, process boundaries have been used to isolate applications running onthe same computer. Each application is loaded into a separate process, which isolates the one applicationfrom other applications running on the same computer. The applications are isolated to provide processsecurity. As a result process cannot make direct call to another process. Instead, IPC techniques have tobe used to have communication in between the processes. Each application is a separate process.

In case of .NET Framework, Application domains provide a secure and versatile unit of processingthat the CLR can use to provide isolation between applications. Several application domains can be run ina single process with the same level of isolation that would exist as separate processes, but withoutincurring the additional overhead of making IPC calls or switching between processes.

A process is divided into number of application domain, where each application domain corresponds toseparate application. But there is clear isolation between them with the advantage of easily sharing data.

Figure 1.10 : Single process for multiple application domain in .NET execution environment

The ability to run multiple applications within a single process increases server scalability and overallefficiency.

2.6 COMMON TYPE SYSTEM

The Common Type System (CTS) defines how types are declared, used, and managed in the runtime.It is an important for Language Interoperability. The CTS performs the following functions:

l Establishes a common framework that enables cross-language integration, type safety, and highperformance code execution.

l Provides an object-oriented model.

PROCESS

Application Domain : Application 1 uses some part of virtual memory :

Application Domain : Application 2 uses some part of virtual memory :

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l Defines rules that languages must follow, so that different languages can interact with eachother.

This section describes concepts and defines terms that will help you understand and work with languageimplementation of the CTS.

Classification of types

The CTS supports two categories:

1. Value types

2. Reference types

The following diagram illustrates type classification described in above paragraphs.

Figure 1.11 : Type Classification

Value types directly stores data in the variable. Value types can be built-in type, user-defined types, orenumerations.

Reference types store a reference to the data’s memory address. Reference types can be self-describing types, pointer types, or interface types. Self-describing types are further split into arrays andclass types. The class types are user-defined classes, boxed value types, and delegates.

All types derive from the System.Object base type.



2.7 METADATA AND SELF-DESCRIBING COMPONENTS

In the past, a software component (.exe or .dll) written in one language could not use or communicatewith software component written in another language. The solution came in the form of COM components.The .NET Framework makes language interoperation even easier by allowing compilers to put additionalinformation into all compiled modules and assemblies. This information, called Metadata.

Metadata is binary information describing the program. When we compile our code into a PE file,metadata is inserted into one portion of the PE file, while the code is converted to IL and inserted intoanother portion of the PE file. Every type, member which are defined or referenced in a module isdescribed within metadata. When code is executed, the runtime loads metadata into memory and refers itto get information about the code’s classes, members, inheritance, and so on.

Metadata stores the information like:

l Description of the assembly’s operation.

l Assembly Identity (name, version, culture, public key).

l Exported types

l Other dependent assemblies

l Security permissions

l Description of types

l Members like methods, fields, properties, events, nested types, etc.

l Attributes

Benefits of Metadata

Metadata allows .NET languages to describe themselves in a language-neutral manner. It givesrequired information to CLR to perform much of its functionalities. The presence of metadata makes theassembly Self-describing file. The CLR modules or components or other assemblies which want tocommunicate with each other uses these information stored in metadata to perform their tasks.

2.8 COMMON LANGUAGE SPECIFICATIONS

What is the Common Language Specification?

To fully interact with other objects regardless of the language they were implemented in, objects mustfollow some implementation rules. For this reason, a set of language features has been defined, called the

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Common Language Specification (CLS). The CLS rules define a subset of the CTS i.e., all the rulesthat apply to the CTS apply to the CLS. The CLS helps enhance and ensure language interoperability bydefining a set of features to the developers.

Most of the members defined in the .NET Framework base class library are CLS-compliant. However,some types in the class library have one or more members that are not CLS-compliant. These membersenable support for language features that are not in the CLS and to support backward compatibility.

The CLS is large enough to include the language constructs that are commonly needed by developers,yet small enough that most languages are able to support it. The details for the CLS compliant featuresare given in MSDN .NET framework developer’s guide. These details are out of the scope of this coursematerial.

2.9 .NET FRAMEWORK CLASS LIBRARY

The .NET Framework Base Class Library is a set of managed classes that provide access to systemservices. File handling, sockets, database access, remoting, and XML are some of the services availablein the Base Class Library. All the .NET languages rely on the same managed classes of Base ClassLibrary for the same services. It can be told that if you have learned any one .NET language, thenworking with other .NET languages will be easy. The same classes, methods, parameters, and types areused for all the system services regardless of any .NET language.

Let us look at the following code that writes to and then reads from a file.

//Here is the C# version of the program. using System; using System.IO; static public void Main() { StreamWriter sw1=new StreamWriter("temp.txt", true); string tempstring="Hi, this is Gopal"; sw1.WriteLine(tempstring); sw1.Close(); StreamReader sr1=new StreamReader("temp.txt"); string filestring=sr1.ReadToEnd(); sr1.Close(); Console.WriteLine(filestring); }

‘Here is the VB.NET version of the program. shared public sub Main() dim sw1 as StreamWriter=new StreamWriter("temp.txt", true)



If we see both versions of the above program are nearly identical. The syntax and use of StreamReader,StreamWriter, and the Console class are identical: same methods, and identical parameters.

.NET Base Class Library includes some 600 managed classes. Microsoft have partitioned the managedclasses of Base Class Library into separate namespaces based on functionality. For example, local input/output can be found in the namespace System.IO. Base Class Library namespaces are often nested. thelevels of namespaces are delimited with dots. System.Runtime.InteropServices, System.Security.Permissions, and System.Windows.Forms are examples of nested namespaces. System is root namespaceand provides classes for all system services.

SUMMARY

.NET Framework is layered architecture. Each layer provides abstraction to the layer above it. CLRprovides a run-time environment, which manages the execution of code and provides essential serviceslike Automatic memory management, language interoperability, security etc. Assembly is a basic elementof packaging in .NET. An assembly consists of IL code and metadata that the application needs to run.Application domains provide a secure and versatile unit of processing that the CLR can use to provideisolation between applications. The CTS defines how types are declared, used, and managed in theruntime. It is an important for Language Interoperability. Metadata is binary information describing theprogram, which are stored in assemblies. CLS is a set of language features has been defined in order tosupport language interoperability. The CLS rules define a subset of the CTS. The .NET Framework BaseClass Library is a set of managed classes that provide access to system services.

QUESTIONS

1. With a neat diagram, explain the .NET Framework architecture.

2. List out the objectives of .NET framework.

3. How the Windows Programming is different from .NET Programming?

4. Define the following

a. CLR

dim tempstring as string= "Hi, this is Gopal" sw1.WriteLine(tempstring) sw.Close() dim sr1 as StreamReader=new StreamReader("temp.txt") dim filestring as string=sr1.ReadToEnd() sr1.Close() Console.WriteLine(filestring) end sub

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b. Managed Code

c. Intermediate Language

d. CTS

e. .NET Base Classes

f. Assemblies

g. CLS

h. Reflection

i. JIT Compilation

j. Manifest

k. Application Domain

l. Garbage Collection

5. What are functionalities of CLR? Give the steps involved in managed execution process.

6. What are assemblies? What are static and dynamic assemblies?

7. How the .NET execution environment with application domain differs from traditional way of execution?

8. What is the function of CTS? Explain the classification of types in CTS with a diagram.

9. Write a note on metadata.

10. ‘It is told that if we learn any one .NET language, then working with other .NET languages will be easy’.

How? Explain with the appropriate example.



Chapter 3

C# Language Tour

By the end of this chapter, you will

8 Have quick survey of C# features

8 Know why to use C#

8 See the first C# program

8 Know the general structure of a C# program

8 Be able to list out difference between C++ and C#

3.1 NEW PROGRAMMING LANGUAGE - C#

C# is new programming language designed for building enterprise applications that run on the .NETFramework. It is written as C#, but pronounced as C Sharp. C# is an evolution of C and C++. Many C++language features and syntax statements, expressions, and operators are used by C#.

It is a pure object oriented language. Compilation of C# code produces managed code, which has thebenefits from the services of the common language runtime, such as language interoperability, enhancedsecurity, and garbage collection. C# has many advanced improvement in type safety, versioning, events,and garbage collection.


34

3.2 WHY C#

C# is a new language form Microsoft which is completely object-oriented. It has been developed fromscratch on .NET framework with the intension to make use of all service of .NET framework in efficientmanner. Important features of C# language design are:

l C# is an elegant, simple, type-safe, object-oriented language.

l C# has the capability to build durable system-level components due to following features:

l Full COM/Platform support for existing code integration.

l Robustness through garbage collection and type safety.

l Security provided through good design.

l Full support of extensible metadata concepts.

l C# supports Language Interoperability and Platform Independence due to following features:

l Full interoperability with COM and .NET Framework services, through tight .NET LibraryBase classes.

l XML support for web-based component interaction.

l Versionability.

3.3 THE C# VERSION OF HELLO WORLD!

As in any other languages, we will also start our first C# program with a simple “Hello World!” stringdisplay program.

The important points to be noted in this program are:

l Comments

l The Main Method

// A Simple "Hello World!" string display program in C# class Hello { static void Main() { System.Console.WriteLine("Hello World!"); } }

Chapter 3 - C# Language Tour


l Input and Output

l Compilation and Execution

Comments

Comments are used for proper documentation of the code. The compiler does not consider the commentsas the part of code. Compiler ignores the comments during the time of compilation. Comments make theprogram more understandable. C# adopts the C++ style of comments.

The first line is a comment:// A “Hello World!” program in C#

The characters // convert the rest of the line to a comment. You can also comment a block of text byplacing it between the characters /* and */, for example:

/* A “Hello World!” program in C#.

This program displays the string “Hello World!” on the screen. */

The Main Method

The C# program must contain a Main method, in which control starts and ends. You can create objectsand execute other methods within this Main method. Note that the alphabet ‘M’ in Main is uppercase,where as in C and C++ it is lowercase. The Main method is a static method and resides inside a class. Inthe “Hello World!” example, it resides inside the ‘Hello’ class.

There are three ways to declare the Main method:

The parameter of the Main method is a array of string which is command-line arguments.

yReturn type void: static void Main() { ... }

Return type int: static int Main() { ... return 0; }

Passing arguments static int Main(string[] args) { ... return 0; }

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Input and Output

In the above Hello World program there is only one output statement, no input statements. The statement:

System.Console.WriteLine(“Hello World!”);

uses the WriteLine method, of the Console class which resides in the .NET run-time library. Thismethod displays its string parameter on the standard output followed by a new line. There are many otherConsole methods are used for different input and output operations. If you include the following using

statement at the beginning of the program:

using System;

you can directly use the System classes and methods as show below. For example:

Console.WriteLine(“Hello World!”);

Compilation and Execution

The compile and execution commands given here are for command line compiler. We are not goinginto the Visual C# IDE. Follow the below steps to compile and execute a program.

l By using any text editor create a source file and save it as Hello.cs. The C# source code filesshould have .cs extension.

l To compile the program use the command given below. If there are no compilation errorsHello.exe is created

csc Hello.cs

l To run the program, enter the command

Hello

3.4 GENERAL STRUCTURE OF A C# PROGRAM

C# program can consist of one or more files. Each file can contain one or more namespaces. A

namespace contains group of related types such as classes, structs, interfaces, enumerations, and delegates.Namespaces may be nested. The following is the skeleton of a C# program that contains all of theseelements.



3.5 USING FULLY QUALIFIED NAMES

Fully Qualified Names describe the logical hierarchy of the type or object. Namespaces and typesalways have unique names. For example, If there are 2 class with same name but are present in differentnamespaces then both the objects will have their unique fully qualified names.

// A skeleton of a C# program using System; namespace Namespace1 { class Class1 { } struct Struct1 { } interface Interface1 { } delegate int Delegate1(); enum Enum1 { } namespace Namespace2 { } class Class2 { public static void Main(string[] args) { } } }

namespace ABC // ABC { class Class1 // ABC.Class1 { } }

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Here the ABC.Class1 and XYZ.Class1 are two different types, even if the class name is same.

In the following code example shows the nested classes and namespaces. Carefully examine the fullyqualified names given as comments.

From the above code example:

l The namespace ABC is a member of the global namespace. Its fully qualified name is ABC.

l The namespace XYZ is a member of ABC. Its fully qualified name is ABC.XYZ.

l The class Class1 is a member of the ABC. Its fully qualified name is ABC.Class1.

l The class name Class2 is used twice in this code. However, the fully qualified names areunique. The first one is declared inside Class1; thus its fully qualified name is: ABC.Class1.Class2.The second is declared inside a namespace XYZ; thus, its fully qualified name isABC.XYZ.Class2.

Using the preceding code segment, you can add a new class member Class3 to the namespaceABC.XYZ as follows:

namespace XYZ // XYZ { class Class1 // XYZ.Class1 { } }

namespace ABC // ABC { class Class1 // ABC.Class1 { class Class2 // ABC.Class1.Class2 { } } namespace XYZ // ABC.XYZ { class Class2 // ABC.XYZ.Class2 { } } }

namespace ABC.XYZ { class Class3 // ABC.XYZ.Class3 { } }



3.6 COMPARISON BETWEEN C++ AND C#

C# has the flavor of C++. C# resembles C++ in its syntax but has many important differences. Aoverview on most important differences between two languages are given below:

n C# is purely object-oriented language, whereas C++ support object-oriented programming.

n Arrays: The syntax of declaring C# arrays is different from that of C++ arrays. The tokens “[]”appear following the array type in C#.

n The bool type in C#: There is no conversion between the bool type and int.

n The long type: In C#, the long data type is 64 bits, while in C++, it is 32 bits.

n The struct type: In C#, classes and structs are semantically different. A struct is a value type,while a class is a reference type.

n The switch statement: Unlike the C++ switch statement, C# does not support fall through fromone case label to another.

n The delegate type: Delegates are roughly similar to function pointers in C++, but they are type-safe and secure.

n Preprocessor directives are used for conditional compilation. No header files are used in C#.

n C# operators: C# supports additional operators such as is and typeof. It also introduces differentfunctionality of some logical operators.

n The Main method is declared differently from the main function in C++. The usage of thecommand-line arguments is also different.

n Method parameters: C# supports ref and out parameters, which are used instead of pointers inpassing parameters by reference.

n Pointers are allowed in C# but only in unsafe mode.

n Overloading operators is performed differently in C#.

n Strings: C# strings are different from C++ strings.

n The foreach keyword allows you to iterate through arrays and collections.

n No global methods or variables in C#: Methods and variables must be contained within a typedeclaration (such as class or struct).

n No header files or #include directives in C#: The using directive is used to reference types inother namespaces without fully qualifying the type names.

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n Destructors: In C#, you don’t have control over when a destructor is called because destructorsare called automatically by the garbage collector.

n Constructors: Unlike C++, if you don’t provide a class constructor in C#, a default constructoris automatically generated for you. The default constructor initializes all the fields to their defaultvalues.

n C# does not support bit fields.

SUMMARY

C# is new programming language, which is purely object oriented and designed for building enterpriseapplications that run on the .NET Framework. It is written as C#, but pronounced as C Sharp.

C# program has the general structure as - it consist of one or more files. Each file can contain one ormore namespaces. A namespace contains group of related types such as classes, structs, interfaces,enumerations, and delegates. Namespaces and types always have unique fully qualified names. C# hasthe flavor of C++ but is much more modern object oriented language.

QUESTIONS

1. List out the important features of C#.

2. Write a program in C# to display ‘Welcome to the world of C Sharp’. Explain the program.

3. Explain the general structure of a C# program.

4. How do namespaces and types in C# have unique names? Give an example.

5. List out the difference between C# and C++.




Chapter 4

C# Language Specifications

In this chapter, you will

8 Study types and variables of C# language

8 Automatic memory management concept with example

8 Expressions and statements in C#

8 Study C# features like structs, interfaces, delegates and enums

8 Know what are namespaces and attributes

4.1 TYPES

In C# language the types are divided into two categories:

1. Value types

2. Reference types

A third category pointers, is available only in unsafe code.

Variables of the value types directly contain their data, whereas variables of the reference types storeaddress of their data. With reference types, it is possible for two variables to reference the same object.With value types, the variables have their own copy of the data.

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C# provides a set of predefined types which are identified through reserved words. The below tablegives predefined types, description and examples.

Table 4.1 : Lists of predefined types in C#

A variable of a type always stores a data value of that type. But in case of reference types, it ispossible for a data to be null or to reference an object of other derived type.

Assignment to a value type variable creates a copy of the value being assigned. Whereas the assignmentto a reference type variable, copies the address of object.

A reference type is a class type, an string type, an interface type, an array type, or a delegate type.

Boxing and Unboxing is a central concept in a C# type system. It provides a bridge between value-types and reference-types by allowing any data of a value-type to be converted to object and from objectto data of value type. Boxing and Unboxing gives the way wherein, a value of any type can ultimately betreated as an object.

Type Description Examples

Sbyte 8-bit signed integral type Sbyte val = 12;

Short 16-bit signed integral type Short val = 12;

Int 32-bit signed integral type int val = 12;

Long 64-bit signed integral type long val1 = 12; long val2 = 34L;

Byte 8-bit unsigned integral type byte val1 = 12; byte val2 = 34U;

Ushort 16-bit unsigned integral type Ushort val1 = 12; ushort val2 = 34U;

Uint 32-bit unsigned integral type uint val1 = 12; uint val2 = 34U;

Ulong 64-bit unsigned integral type ulong val1 = 12; ulong val2 = 34U; ulong val3 = 56L; ulong val4 = 78UL;

Float Single-precision floating point type float value = 1.23F;

Double Double-precision floating point type Double val1 = 1.23 double val2 = 4.56D;

Bool Boolean type; a bool value is either

true or false bool value = true;

Char Character type is a Unicode character char value = 'h';

decimal Precise decimal type with 28

significant digits Decimal value = 1.23M;

Chapter 4 - C# Language Specifications


4.2 VARIABLES AND PARAMETERS

Variables represent storage locations. Every variable has a type that determines what kind of data canbe stored in the variable. C# is a type-safe language, the C# compiler guarantees that values stored invariables are always of the correct type. Variables can be initially assigned or initially not assigned.

C# variable declaration have following syntax[optional_modifier] datatype identifier;

Where optional_modifier is accessibility form

There are seven categories of variables:

l Static variables

l Instance variables

l Array elements

l Value parameters

l Reference parameters

l Output parameters

l Local variables

Let us see each of these categories in detail.

Static variables

A variable declared with the static modifier is called a static variable. There will be only one copy ofthe variable, regardless of how many instances of class (class in which static variable exists) are created.

Instance variables

A variables declared without the static modifier is are instance variables.

Array elements

The array is a container that has a list of storage locations for a specified type. The elements for aspecified type of an array come into existence when an array instance is created, and exist until there areno references to that array instance.

Value parameters

Parameters are arguments passed to the function. A parameter declared without a ref or out modifier

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is a value parameter. A value parameter comes into existence when the function is invoked and is initializedwith the value of the argument passed. A value parameter exists until the function returns.

Reference parameters

A parameter declared with a ref modifier is a reference parameter. A reference parameter does notcreate a new instance, it points to the same storage location of the parameter passed as an argument.Thus, a variable must be definitely initialized before it is passed as a reference parameter to a function.

Output parameters

A parameter declared with an out modifier is an output parameter. A reference parameter does notcreate a new instance, it points to the same storage location of the parameter passed as an argument.Thus, a variable need not be initialized before it is passed as a reference parameter to a function. Butoutput parameter must be definitely assigned before the function returns.

Local variables

A local variable is declared and exits within a block, a for-statement, a switch-statement, or using-statement. A local variable is not automatically initialized and thus has no default value.

4.3 AUTOMATIC MEMORY MANAGEMENT

Manual memory management requires developers to manage the allocation and de-allocation of blocksof memory. Manual memory management can be both time-consuming and difficult. In C#, automaticmemory management is provided so that developers are freed from this burdensome task. Automaticmemory management increases code quality and enhances developer productivity without negative impacton either expressiveness or performance. The example

using System; public class Stack { private Node first = null; public bool Empty { get { return (first == null); } } public object Pop() { if (first == null)



shows a Stack class implemented as a linked list of Node instances. Node instances are created in thePush method and are garbage collected when no longer needed. A Node instance becomes eligible forgarbage collection when it is no longer possible for any code to access it. For instance, when an item isremoved from the Stack, the associated Node instance becomes eligible for garbage collection. Theexample

shows code that uses the Stack class. A Stack is created and initialized with 10 elements, and then innext statement it is assigned the value null. Once the variable s is assigned null, the Stack and the associated10 Node instances become eligible for garbage collection. The garbage collector is permitted to clean upimmediately. The garbage collector keeps moving around the objects in memory, but this motion is invisibleto most C# developers.

Console.Write("Can't Pop from an empty Stack."); else { object temp = first.Value; first = first.Next; return temp; } } public void Push(object o) { first = new Node(o, first); } class Node { public Node Next; public object Value; public Node(object value): this(value, null) {} public Node(object value, Node next) { Next = next; Value = value; } } }

class Test { static void Main() { Stack s = new Stack(); for (int i = 0; i < 10; i++) s.Push(i); s = null; } }

46

C# provides the ability to write “unsafe” code. Such code can deal directly with pointer types andobject addresses, however, C# requires the programmer to fix objects to temporarily prevent the garbagecollector from moving them. This “unsafe” code feature is in fact a “safe” feature from the perspectiveof both developers and users. Unsafe code must be clearly marked in the code with the modifier unsafe,so developers can not possibly use unsafe language features accidentally, and the compiler and the executionengine work together to ensure that unsafe code cannot masquerade as safe code. These restrictions limitthe use of unsafe code to situations in which the code is trusted. The example

shows an unsafe block in a method named WriteLocations that fixes an array instance and usespointer manipulation to iterate over the elements. The index, value, and location of each array element arewritten to the console. One possible example of output is:

but, of course, the exact memory locations may be different in different executions of the application.

using System; class Test { static void WriteLocations(byte[] arr) { unsafe { fixed (byte* pArray = arr) { byte* pele = pArray; for (int i = 0; i < arr.Length; i++) { byte value = *pele; Console.WriteLine("arr[{0}] at 0x{1:X} is {2}", i, (uint)pele, value); pele++; } } } } static void Main() { byte[] arr = new byte[] {1, 2, 3, 4, 5}; WriteLocations(arr); }

arr[0] at 0x8E0360 is 1 arr[1] at 0x8E0361 is 2 arr[2] at 0x8E0362 is 3 arr[3] at 0x8E0363 is 4 arr[4] at 0x8E0364 is 5



4.4 EXPRESSIONS AND OPERATORS

An expression is a sequence of operators and operands that specifies computation and assigns theresult to a variable. This section defines the syntax, order of evaluation of operators, and meaning ofexpressions.

Expressions are constructed from operands and operators. The operators of an expression indicatewhich operations to perform. Examples for operators are +, -, *, /, etc. Examples for operands are literals,variables, and expressions.

There are three kinds of operators:

1. Unary operators: The unary operators operate on only one operand.

For example: –x, x++, etc.

2. Binary operators: The binary operators operate on two operands.

For example: x + y.

3. Ternary operator: There is only one ternary operator, ?:. The ternary operator operates onthree operands.

For example: condition? true_exp: false_exp

The order of evaluation of operators in an expression is determined by the precedence and associativityof the operators. When an expression contains multiple operators, the precedence of the operators controlthe order in which the individual operators are evaluated. For example, the expression x + y * z is evaluatedas x + (y * z) because the * operator has higher precedence than the + operator.

The following table summarizes operator’s order of precedence from highest to lowest:

Category Operators Primary x.y f(x) a[x] x++ x-- new

typeof checked unchecked Unary + - ! ~ ++x --x (T)x Multiplicative * / % Additive + - Shift << >> Relational and testing < > <= >= is as Equality == != Logical AND & Logical XOR ^

48

Table 4.2 : Operator Precedence Table

When an operand occurs between two operators with the same precedence, the associatively of theoperators controls the order in which, the operation is performed. Precedence and associativity can becontrolled using parentheses. For example, a + b * c first multiplies b by c and then adds the result to a, but(a + b) * c first adds a and b and then multiplies the result by c. The assignment operators and theconditional operator (?:) are right-associative, i.e., operations are performed from right to left. For example,a = b= c is evaluated as a = (b = c).

4.5 STATEMENTS

C# provides a variety of statements. Most of these statements are similar to that of C and C++.

4.5.1 Blocks

A block permits multiple statements to be written as group. A block consists of list of single statementsenclosed in braces.

If the statement list within braces is omitted, the block is said to be empty.

4.5.2 The empty statement

An empty statement (;) is used when there are no operations to perform, but require an statement.Execution of an empty statement simply transfers control to the end point of the statement. An emptystatement can be used when writing a while statement with a null body:

Logical OR | Conditional AND && Conditional OR || Conditional ?: Assignment = *= /= %= += -= <<= >>= &= ^= |=

{ // Begin a block Bool flag; flag = true; CallFunction(flag); } // End a block



4.5.3 Labeled statements

A labeled statement is prefixed by a label. Labeled statements are permitted in blocks. A label is aname given by the identifier. The scope of a label is the block in which the label is declared. If two labelshave same name we get compile time error.

A label can be referenced from goto statements within the scope of the label. Labels and otheridentifiers can have same name .

The example

is valid and uses the name abc as both a parameter and a label.

4.5.4 Selection statements

Selection statements select one of a number of possible statements for execution based on the resultof an expression. In this section we will see few selection statements:

The if statement

The if statement executes the if block of a boolean expression result is true.

int Func(int abc) { if (abc >= 0)

goto abc; abc = -abc; abc: return abc; }

while (WaitForAnEvent()) ;

An empty statement can also be used to declare a label just before the closing “}” of a block:

void Func(){

...if (true) goto exit;...

exit: ;}

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An else part is can also be associated with the above if statement. The else block will be executedwhen the boolean expression result is false.

The switch statement

A switch statement executes the statements that are associated with the value of a given expression,or default of statements if no match exists. The example demonstrates the switch usage how this statementswitches on the number of arguments provided.

The switch expression must be an integer type, char or a string. The case labels have to be constants.The end of a case statement must explicitly state where to go next. The break statement takes the controlto go out of switch statement.

if (Boolean_expression) { // if block statements }

if (Boolean_expression) { // if block is executed if Boolean_expression is true } else { // else block is executed if Boolean_expression is false }

class TestSwitch{

static void Main(string[] args){

switch (args.Length){

case 0: Console.WriteLine(“No arguments were provided”); break;case 1: Console.WriteLine(“One arguments was provided”); break;default: Console.WriteLine(“{0} arguments were provided”,

args.Length); break;

}}

}



using System;

class SwitchSelect{

public static void Main(){

string myInput;int myInt;

begin:Console.Write(“Please enter a number between 1 and 3: “);myInput = Console.ReadLine();myInt = Int32.Parse(myInput);

// switch with integer typeswitch (myInt){

case 1: Console.WriteLine(“Your number is {0}.”, myInt); break;case 2: Console.WriteLine(“Your number is {0}.”, myInt); break;case 3: Console.WriteLine(“Your number is {0}.”, myInt); break;default: Console.WriteLine(“Your number {0} is not between 1 and 3.”,myInt);

}

decide:Console.Write(“Type \”continue\” to go on or \”quit\” to stop: “);myInput = Console.ReadLine();

// switch with string typeswitch (myInput){

case “continue”: goto begin;case “quit”: Console.WriteLine(“Bye.”); break;default: Console.WriteLine(“Your input {0} is incorrect.”, myInput); goto decide;

}}

}

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4.5.5 Iteration statements

Iteration statements repeatedly execute a block of statements. The number of iterations depends onthe condition represented by boolean expression. The block of code will be iterated until the condition istrue.

There are four iteration statement in C#:

1) while statement

2) do statement

3) for statement

4) foreach statement

The while statement

A while statement conditionally executes a statement zero or more times, as long as a boolean expressionis true. For example, the program given below uses a while statement to find the position of first occurrenceof a value in an array.

The do statement

A do statement conditionally executes a statement one or more times. The block is executed atleast

using System;

class TestWhile{

static int Find(int value, int[] arr){

int i = 0;while (arr[i] != value){

if (++i > arr.Length) return arr.Length;

}return i;

}

static void Main(){

Console.WriteLine(Find(3, new int[] {5, 4, 3, 2, 1}));}

}



once, and continues to execute until the condition or boolean expression in true. The below programdemonstrates the usage of do statement. This program reads from the console until the “Exit” string isentered.

The for statement

A for statement evaluates a sequence of initialization expressions and repeatedly executes the blockof statements until a condition is true. The below example uses a for statement to write out the integervalues 1 through 10.

The foreach statement

A foreach statement lets us iterate over the elements in arrays and collections. The elements of single-dimensional arrays are traversed in increasing order of index, starting with index 0 to Length – 1. Theelements of multi-dimensional arrays elements are traversed such that the indices of the rightmost dimensionare incremented first, then the next left dimension, and so on to the left. The below example uses aforeach statement to iterate over the elements of an array.

using System;

class Test{

static void Main(){

string s;do{

s = Console.ReadLine();}while (s != “Exit”);

}}

using System;

class Test{

static void Main(){

for (int i = 0; i < 10; i++) Console.WriteLine(i);

}}

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Jump statements

Jump statements unconditionally transfer control. Different jump statements supported by C# are:

l break statement

l continue statement

l goto statement

l return statement

l throw statement

The above given jump statements perform same function as in any other languages like C, C++ orJava. The below table lists the kinds of jump statements and provides an example for each.

using System;

class TestForeach{

static void Main(){

int[] array1 = new int[] {1,2,3,4,5};foreach (int i in array1) Console.WriteLine(“Value is {0}”, i);

}}

break statements static void Main(string[] args) { int i = 0; while (true) { if (i == args.Length) break; Console.WriteLine(args[i++]); } }

continue statements static void Main(string[] args) { int i = 0; while (true) { Console.WriteLine(args[i++]); if (i < args.Length) continue; break; } }



Table 4.3 : List of jump statements and their description

The break statement exits the nearest enclosing switch, while, do, for, or foreach statement. Thecontinue statement starts a new iteration of the nearest enclosing while, do, for, or foreach statement. Thegoto statement transfers control to a statement that is marked by a label. The return statement returnscontrol to the caller function. The throw statement throws an exception.

checked and unchecked statements

The checked and unchecked statements are used to control the overflow checking for integer typearithmetic operations and conversions. The checked statement causes all expressions in the checkedblock to be evaluated in a checked context, and the unchecked statement causes all expressions in theunchecked block to be evaluated in an unchecked context.

The example for these statements

return statements static int add(int a, int b) { return a + b; } static void Main() { Console.WriteLine(add(1, 2)); return; }

throw statements and try statements

static int F(int a, int b) { if (b == 0) throw new Exception("Divide by zero"); return a / b; } static void Main() { try { Console.WriteLine(F(5, 0)); } catch(Exception e) { Console.WriteLine("Error"); } }

static void Main(){ int x = Int32.MaxValue; Console.WriteLine(x + 1); // Overflow checked { Console.WriteLine(x + 1); // Exception } unchecked { Console.WriteLine(x + 1); // Overflow }}

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lock statements

The lock statement obtains the mutual exclusion lock for a given object, executes statements, and thenreleases the lock. The example is shown below

using statements

The using statement obtains one or more resources, executes statements, and then releases of theresource.

4.6 STRUCTS

Structs are similar to classes, they represent data structures that can contain data members and alsofunction members. The difference is structs are value types and classes are reference type. A variable ofa struct type directly contains the data of the struct, whereas a variable of a class type contains a referenceto the object. Structs are useful for small data structures. The primitive types provided by C#, such as int,double, and bool, are in fact all struct types.

Let us see an example, that use of a struct rather than a class for a Point can make a large differencein the number of allocations. The program below creates and initializes an array of 100 points.

With Point implemented as a class, the program creates 101 separate objects, one for the array andone each for the 100 elements.

static void Main(){ A a = ...; lock(a) { a.P = a.P + 1; }}

static void Main(){ using (Resource r = new Resource())

{ r.Func(); }

}



If Point is implemented as a struct, instead of classes, then the program creates just one object, for thearray. The Point objects are allocated in-line within the array.

class Point{

public int x, y;

public Point(){

x = 0;y = 0;

}

public Point(int x, int y){

this.x = x;this.y = y;

}}

class Test{

static void Main(){

Point[] points = new Point[100];for (int i = 0; i < 100; i++)

points[i] = new Point(i, i*i);}

}

struct Point{

public int x, y;public Point(int x, int y){

this.x = x;this.y = y;

}}

class Test{

static void Main(){

Point[] pointStruct = new Point[100];for (int i = 0; i < 100; i++)

pointStruct[i].Point(i, i*i);}

}

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4.7 INTERFACES

The interface keyword declares a reference type that has abstract members. Interfaces are used todefine a contract; a class or struct that implements the interface must obey to this contract. Interfacescan contain methods, properties, indexers, and events as members. They can not contain constants, fields(private data members), constructors and destructors or any type of static member. All the members ofan interface are public by definition.

The example

shows an interface that contains an indexer, an event E, a method Func, and a property P. Interfacesmay employ multiple inheritance. In the example

the interface IComboBox inherits from both ITextBox and IListBox. Classes and structs can implementmultiple interfaces. In the example

interface IExample{ string this[int index] { get; set; } event EventHandler E; void Func(int value); string P { get; set; }}public delegate void EventHandler(object sender, EventArgs e);

interface IControl{ void Paint();}

interface ITextBox: IControl //ITextBox inherits IControl{ void SetText(string text);}

interface IListBox: IControl //IListBox inherits IControl{ void SetItems(string[] items);}

interface IComboBox: ITextBox, IListBox {}

interface IDataBound{ void Bind(Binder b);}



the class EditBox derives from the class Control and implements both IControl and IDataBound.

In the previous example, the Paint method from the IControl interface and the Bind method fromIDataBound interface are implemented using public members on the EditBox class. C# provides analternative way of implementing these methods that allows the implementing class to avoid having thesemembers be public. Interface members can be implemented using a qualified name. For example, theEditBox class could instead be implemented by providing IControl.Paint and IDataBound.Bind methods.

Interface members implemented in this way are called explicit interface members because eachmember explicitly designates the interface member being implemented. Explicit interface members canonly be called via the interface. For example, the EditBox’s implementation of the Paint method can becalled only by casting to the IControl interface.

4.8 DELEGATES

A delegate is a C# language element that allow us to reference a method. For a C or C++ programmer,this is a familiar because a delegate is basically like a function pointer. However, unlike function pointers,delegates are object-oriented and type-safe.

A delegate declaration defines a class that is derived from the class System.Delegate. A delegateinstance encapsulates one or more methods, each of which is referred to as a callable entity. For instance

public class EditBox: Control, IControl, IDataBound{ public void Paint() {...} public void Bind(Binder b) {...}}

public class EditBox: IControl, IDataBound{ void IControl.Paint() {...} void IDataBound.Bind(Binder b) {...}}

class Test{ static void Main() { EditBox editbox = new EditBox(); editbox.Paint(); // error: no such method IControl control = editbox; control.Paint(); // calls EditBox’s Paint implementation }}

60

methods, a callable entity consists of an instance and a method on that instance. For static methods, acallable entity consists of just a method. Given a delegate instance and an appropriate set of arguments,one can invoke all of that delegate instance’s methods with that set of arguments.

An interesting and useful property of a delegate instance is that it does not know about the classes ofthe methods it encapsulates; all that matters is that those methods be compatible with the delegate’s type.This makes delegates perfectly suited for “anonymous” invocation. This is a powerful capability.

There are three steps in defining and using delegates: declaration, instantiation, and invocation. Delegatesare declared using delegate declaration syntax. The example

creates a SimpleDelegate instance and then immediately calls it.

There is not much point in instantiating a delegate for a method and then immediately calling thatmethod via the delegate, as it would be simpler to call the method directly. Delegates really show theirusefulness when their anonymity is used.

The example

delegate void SimpleDelegate();

declares a delegate named SimpleDelegate that takes no arguments and returns no result.

The example

class Test{ static void F() { System.Console.WriteLine(“Test.F”); }

static void Main() { SimpleDelegate dele = new SimpleDelegate(F); dele(); }}

void MultiCall(SimpleDelegate dele, int count){ for (int i = 0; i < count; i++) { dele(); }}



shows a MultiCall method that repeatedly calls a SimpleDelegate. The MultiCall method does notknow or care about the type of the target method for the SimpleDelegate, what accessibility that methodhas, or whether or not that method is static. All that matters is that the target method is compatible withSimpleDelegate.

4.9 ENUMS

An enum type declaration defines a type name for a related group of symbolic constants. Enums areused for “multiple choice”, in which a runtime decision is made from a fixed number of choices that areknown at compile-time.

The example

shows a Color enum and a method that uses this enum. The signature of the Fill method makes it clearthat the shape can be filled with one of the given colors.

The use of enums is superior to the use of integer constants (as is common in languages without

enum Color{ Red, Blue, Green}

class Shape{ public void Fill(Color color) { switch(color) {

case:Color.Red:Console.WriteLine(“RED”);break;

case:Color.Blue:Console.WriteLine(“BLUE”);break;

case:Color.Green:Console.WriteLine(“GREEN”);break;

default:break;

} }}

62

enums) because the use of enums makes the code more readable and self-documenting. The self-documenting nature of the code also makes it possible for the development tool to assist with code writingand other “designer” activities. For example, the use of Color rather than int for a parameter type enablessmart code editors to suggest Color values.

4.10 NAMESPACES

C# programs are organized using namespaces. Namespaces are used both as an “internal” organizationsystem for a program, and as an “external” organization system. This is a way of writing program elementsthat are exposed to other programs.

A namespace declaration consists of the keyword namespace, followed by a namespace name andbody.

Classes actually contain data and Namespaces are used to logically arrange classes. Namespaces canalso contain many other Namespaces and classes. C# programs are organized using namespaces.Namespaces provide a way to group classes, by providing an extra level of naming beyond the classname.

Namespaces are implicitly public and the declaration of a namespace does not include any accessmodifiers. The identifier or name of a namespace may be a single identifier or a sequence of identifiersseparated by “.” tokens. The later form permits a program to define a nested namespace. For example,

is equivalent to

namespace NamespaceName{ ... // namespace body}

namespace ABC.XYZ{ class A {} class B {}}

namespace ABC{ namespace XYZ { class A {} class B {} }}



or it can also be written as

All the above three fragments of code are equivalent.

We know that the namespaces can be nested. Many namespaces in the base class library are nested.Prefixing each and every library calls with the namespace can get quite cumbersome. To avoid this overtyping, use ‘using’ statement. Let us see the below program which shows the usage of ‘using’ statement

4.11 ATTRIBUTES

C# is an imperative language, but like all imperative languages it does have some declarative elements.

namespace ABC.XYZ{ class A {}}

namespace ABC.XYZ{ class B {}}

//Here is a program written without the ‘using’ statement.public class Starter{

static void Main(){

System.Windows.Forms.MessageBox.Show(“Hello, world!”);System.Console.WriteLine(“Hello, world”);

}}

//This the same program written with the ‘using’ statement. This is a//simpler one.

using System;

using System.Windows.Forms;

public class Starter{

static void Main(){

MessageBox.Show(“Hello, world!”);Console.WriteLine(“Hello, world”);

}}

64

For example, the accessibility of a method in a class is specified by declaring it public, protected, internal,protected internal, or private. C# generalizes this capability, so that programmers can invent new kinds ofdeclarative information, attach this declarative information to various program entities, and retrieve thisdeclarative information at run-time. Programs specify this additional declarative information by definingand using attributes.

For instance, a framework might define a HelpAttribute attribute that can be placed on programelements (such as classes and methods) enabling developers to provide a mapping from program elementsto help documentation for them. The example

defines an attribute class named HelpAttribute, that has one positional parameter (string url) and onenamed parameter (string Topic). Positional parameters are defined by the formal parameters for publicinstance constructors of the attribute class, and named parameters are defined by public non-static read-write fields and properties of the attribute class.

The example

shows several uses of the attribute Help.

Attribute information for a given program element can be retrieved at run-time by using reflectionsupport. The example

using System;

public class HelpAttribute: Attribute{ public HelpAttribute(string url) { this.url = url; }

public string Topic = null; private string url;

public string Url { get { return url; } }}

[Help(“http://www.mycollege.com/.../Class1.htm”)]public class Class1{ [Help(“http://www.mycollege.com/.../Class1.htm”, Topic = “F”)] public void F() {}}



checks to see if Class1 has a HelpAttribute, and writes to the console the associated Topic and Urlvalues if the attribute is present.

SUMMARY

This chapter covers the C# language specification. In C# language two categories of types - Valuetypes and Reference types. There are seven categories of C# variables - Static variables, Instancevariables, Array elements, Value parameters, Reference parameters, Output parameters and Localvariables. The expressions and statements are same as in C++, except foreach looping statement whichiterate over the elements in arrays and collections. Structs are similar to classes, it also contains datamembers and function members. Except Structs are value types and Classes are reference type. Interfacesare reference types which are used to implement multiple inheritance. A delegate allows us to referencea method. C# programs are organized using namespaces. Namespaces are used both as an “internal”organization system for a program, and as an “external” organization system. In C# additional declarativeinformation by defining and using attributes.

QUESTIONS

1. Which are two different categories of types in C#?

2. What are variables? How many categories of variables are there in C#? Define each.

3. What is the importance of automatic memory management? Explain with example.

4. Write a note on expressions and operators in C#.

5. What are empty statement and labeled statements? Why are they used?

using System;

class Test{ static void Main() { Type type = typeof(Class1); object[] arr = type.GetCustomAttributes(typeof(HelpAttribute), true); if (arr.Length == 0) Console.WriteLine(“Class1 has no Help attribute.”); else { HelpAttribute ha = (HelpAttribute) arr[0]; Console.WriteLine(“Url={0}, Topic={1}”, ha.Url, ha.Topic); } }}

66

6. What is an iterative statement? Explain foreach statement with example.

7. Which are different jump statements supported by C#?

8. What are checked and unchecked statements? Give example.

9. Give an example lock and using statements.

10. How are structures different from classes in C#?

11. What are interfaces? Give an example.

12. What is a delegate? What is the use of it? Give example

13. Write a program to demonstrate the usage of enums in C#.

14. Write a note on namespaces in C#.

15. What is the use of attributes in C# programs?




Chapter 5

Classes And Inheritance


8 Be knowledged with the classes in C#

8 Know how to implement inheritance in C#

8 Know method overloading concept

5.1 CLASSES

Class declarations are reference types. A class can inherit from another class, and can implementinterfaces. Class members can include constants, fields, methods, properties, events, indexers, operators,instance constructors, destructors, static constructors, and nested type declarations. Each member has anassociated accessibility, which controls the portion of program code that is able to access the member.There are five forms of accessibility. They are summarized in the table below.

Table 5.1 : Accessibility forms

Accessibility Intuitive meaning public Access not limited

protected Access limited to the containing class or types derived from the containing class

internal Access limited to the program protected internal

Access limited to the program or types derived from the containing class

private Access limited to the containing type

68

The declared accessibility of a member can be one of the following:

l Public, which is selected by including a public modifier in the member declaration. The intuitivemeaning of public is “access not limited”.

l Protected internal (meaning protected or internal), which is selected by including both aprotected and an internal modifier in the member declaration. The intuitive meaning ofprotected internal is “access limited to this program or types derived from the containing class”.

l Protected, which is selected by including a protected modifier in the member declaration.The intuitive meaning of protected is “access limited to the containing class or types derivedfrom the containing class”.

l Internal, which is selected by including an internal modifier in the member declaration. Theintuitive meaning of internal is “access limited to the program”.

l Private, which is selected by including a private modifier in the member declaration. Theintuitive meaning of private is “access limited to the containing type”.

The example

using System;

class MyClass{ public MyClass() // Instance constructor { Console.WriteLine(“Instance constructor”); }

public MyClass(int value) // Parameterized Instance constructor { MyField = value; Console.WriteLine(“Instance constructor”); }

~MyClass() // Destructor { Console.WriteLine(“Destructor”); }

public const int MyConst = 20; public int MyField = 40;

public void MyMethod() { Console.WriteLine(“MyClass.MyMethod”); }

Chapter 5 - Classes And Inheritance


shows a class that contains properties, constant, field, event, indexed and method as members. Thebelow class, containing Main method, shows uses of these members.

public int MyProperty { get { return MyField; } set { MyField = value; } }

public int this[int index] { get { return 0; } set { Console.WriteLine(“this[{0}] = {1}”, index, value); } }

public event EventHandler MyEvent;

public static MyClass operator+(MyClass a, MyClass b) { return new MyClass(a.MyField + b.MyField); }

internal class MyNestedClass {}

}

class Test{ static void Main() { // Instance constructor usage MyClass a = new MyClass(); MyClass b = new MyClass(123);

// Constant usage Console.WriteLine(“MyConst = {0}”, MyClass.MyConst);

70

The class members properties, constant, field, event, indexed and method are explained in the followingtopics.

5.2 CONSTANTS

A constant is a class member that represents a constant value. Constant members are initialized at thetime of their declaration. The example

shows a class named Constants that has two public constants.

// Field usage a.MyField++; Console.WriteLine(“a.MyField = {0}”, a.MyField);

// Method usage a.MyMethod();

// Property usage a.MyProperty++; Console.WriteLine(“a.MyProperty = {0}”, a.MyProperty);

// Indexer usage a[3] = a[1] = a[2]; Console.WriteLine(“a[3] = {0}”, a[3]);

// Event usage a.MyEvent += new EventHandler(MyHandler);

// Overloaded operator usage MyClass c = a + b; }

static void MyHandler(object sender, EventArgs e) { Console.WriteLine(“Test.MyHandler”); }

internal class MyNestedClass {}}

class Constants{ public const int A = 1; public const int B = A + 1;}



Constants are considered static members, but constant declaration does not requires the static modifier.Constants can be accessed through the class, as in

which prints out the values of Constants.A and Constants.B, respectively.

5.3 FIELDS

A field is a member that represents a variable associated with an object or class.

The example

shows a Color class that has internal instance fields named redPart, bluePart, and greenPart, andstatic fields named Red, Blue, Green, and White. The use of static fields in this manner is not ideal. Thefields are initialized at some point before they are used, but after this initialization they can be changed.Such a modification to the fields could cause unpredictable errors in other programs that use Color andassume that the values do not change. Readonly fields can be used to prevent such problems. Assignmentsto a readonly field can only occur as part of the declaration, or in an instance constructor or static

using System;

class Test{ static void Main() { Console.WriteLine(“{0}, {1}”, Constants.A, Constants.B); }}

class Color{ internal ushort redPart; internal ushort bluePart; internal ushort greenPart;

public Color(ushort red, ushort blue, ushort green) { redPart = red; bluePart = blue; greenPart = green; }

public static Color Red = new Color(0xFF, 0, 0); public static Color Blue = new Color(0, 0xFF, 0); public static Color Green = new Color(0, 0, 0xFF); public static Color White = new Color(0xFF, 0xFF, 0xFF);}

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constructor in the same class. A static readonly field can be assigned in a static constructor, and a non-static readonly field can be assigned in an instance constructor. Thus, the Color class can be enhanced byadding the modifier readonly to the static fields as shown below

5.4 METHODS

A method is a member that implements a computation or action that can be performed by an object orclass. Methods have a list of formal parameters, a return value and are either static or non-static. Staticmethods are accessed through the class. Non-static methods, which are also called instance methods, areaccessed through instances of the class (objects).

The example

class Color{ internal ushort redPart; internal ushort bluePart; internal ushort greenPart;

public Color(ushort red, ushort blue, ushort green) { redPart = red; bluePart = blue; greenPart = green; }

public static readonly Color Red = new Color(0xFF, 0, 0); public static readonly Color Blue = new Color(0, 0xFF, 0); public static readonly Color Green = new Color(0, 0, 0xFF); public static readonly Color White = new Color(0xFF, 0xFF, 0xFF);}

using System;

public class Stack{ public static Stack Clone(Stack s) {...} public static Stack Flip(Stack s) {...} public object Pop() {...} public void Push(object o) {...} public override string ToString() {...} ...}

class Test



shows a Stack that has several static methods (Clone and Flip) and several instance methods (Pop,Push, and ToString).

Methods can be overloaded, which means that multiple methods may have the same name. Themethod with matching signature is called. The signature of a method consists of the name of the methodand the number, modifiers, and types of its formal parameters. The signature of a method does not includethe return type. The example

{ static void Main() { Stack s = new Stack(); for (int i = 1; i < 10; i++) s.Push(i); Stack flipped = Stack.Flip(s); Stack cloned = Stack.Clone(s); Console.WriteLine(“Original stack: “ + s.ToString()); Console.WriteLine(“Flipped stack: “ + flipped.ToString()); Console.WriteLine(“Cloned stack: “ + cloned.ToString()); }}

using System;

class Test{ static void Func() { Console.WriteLine(“Func()”); }

static void Func(object o) { Console.WriteLine(“Func(object)”); }

static void Func(int value) { Console.WriteLine(“Func(int)”); }

static void Func(ref int value) { Console.WriteLine(“Func(ref int)”); }

static void Func(int a, int b)

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shows a class with a number of methods called Func. The output produced is

Parameter Passing

Passing by value - The parameter modifiers ‘ref’ and ‘out’ relate to how the parameter is passedinto the method. Where neither of these modifiers is used, the parameter is passed in ‘by value’. In thiscase, when the method is called the value given is copied to the variable specified in the method declaration.The following example illustrates this point; note that the change made to variable b in the body of the‘change’ method does not result in a change to the variable a used to invoke the method.

{ Console.WriteLine(“Func(int, int)”); }

static void Func(int[] values) { Console.WriteLine(“Func(int[])”); }

static void Main() { Func(); Func(1); int i = 10; Func(ref i); Func((object)1); Func(1, 2); Func(new int[] {1, 2, 3}); }}

Func()Func(int)Func(ref int)Func(object)Func(int, int)Func(int[])

public static void Main(){

int a = 0; change(a);}

public static void change(int b){ b = 5;}



In this example, it was a value type that was passed ‘by value’. But reference types can also bepassed ‘by value’. We know that, reference type variable is actually holds a memory address. So whenthis variable is passed ‘by value’, the memory address is copied to the variable specified in the method.But of course, because the two variables will hold the same memory address, any changes made withinthe method body to the object located at that memory address will be reflected outside the method.

Passing by reference - In C# we can pass variables into methods ‘by reference’. Where a variableis passed by reference, the ‘ref’ modifier must be used both in the method definition argument list and themethod invocation.

Passing by reference is most obviously useful in cases where we want to treat a value type like areference type. For instance, the method call in the following code does change the value of the variablea passed into the ‘change’ method.

‘output’ parameters - Where a method parameter is defined (and invoked) using the ‘out’ modifier,it is passed by reference. The difference between the ‘out’ and the ‘ref’ modifier is this: a parametermodified by the ‘out’ keyword need not be assigned a value before being passed into the method, but mustbe assigned a value in the method before it is returned.

The reason that one might use output parameters is to return multiple values from a method. Forinstance, in the following code an integer and a boolean is passed to the ‘change’ method. This methodsets the boolean to indicate whether or not the integer is greater than 0, and returns the value of theinteger doubled. So here both boolean and interger result is returned from the method.

public static void Main(){ int a = 0; change(ref a); // After this method invocation, a=5}

public static void change (ref int b){ b = 5;}

public static void Main(){ bool b; int c = change(5, out b);}

public static int change (int a, out bool b){ b=false; if (a>0) b=true; return (2*a);}

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The params modifier - One can pass an arbitrary number of types to a method by declaring aparameter array with the ‘params’ modifier. Note, though, that it is not necessary to place these additionaltypes into an array before calling the method, they can simply be listed in the method invocation.

Types passed as ‘params’ are all passed by value. The following code gives an example of the use ofthe ‘params’ modifier.

The method called ignores the first type passed to it (a double) and returns the sum of all (an arbitrarynumber of) the integer values (b, c and d) passed to it. The param array intArr holds b, c and d values init.

Return Type - Methods can either return a type or not. A method that does not return a type mustgive its return type as ‘void’. A method that does return a type must name the type returned.

A method will stop executing and return a value when it reaches a ‘return’ statement at any point in itsexecution. The type returned is given at the end of such a return statement; its type must correspond withthe type specified in the method declaration. For example, the following piece of code illustrates this point.

public static void Main(){ double a = 1; int b = 2; int c = 3;

int d = 4; int e = total(a, b, c, d);}

public static int total(double a, params int[] intArr){ int sum = 0;

for (int i=0; i < intArr.Length; i++) sum += intArr[i]; return sum;}

public static int exampleMethod(){ int i = 0;

...

return i;}



5.5 PROPERTIES

A property is a member that provides access to a characteristic of an object or a class. Examples ofproperties include the length of a string, the size of a font, the caption of a window, the name of acustomer, and so on. Properties are a natural extension of fields. Both are named members with associatedtypes, and the syntax for accessing fields and properties is the same. However, unlike fields, properties donot denote storage locations. Instead, properties have accessors that specify the block of statements to beexecuted when their values are read or written.

Properties are defined with property declarations. The first part of a property declaration looks quitesimilar to a field declaration. The second part includes a get accessor or a set accessor. In the examplebelow, the Button class defines a Caption property.

Properties that can be both read and written, such as Caption, include both get and set accessors. Theget accessor is called when the property’s value is read and the set accessor is called when the property’svalue is written.

The declaration of properties is relatively straightforward, but the real value of properties is seen whenthey are used. For example, the Caption property can be read and written in the same way that fields canbe read and written:

public class Button{ private string caption; public string Caption { get // get accessor block { return caption; } set // set accessor block { caption = value; Repaint(); } }}

Button b = new Button();b.Caption = “ABC”; // set accessor executedstring s = b.Caption; // get accessor is executedb.Caption += “DEF”; // get & set accessor both are executed

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5.6 EVENTS

An event is a member that enables an object or class to provide notifications. A class defines an eventby providing an event declaration and an optional set of event accessors. The declaration resembles afield declaration, though with an added event keyword. The type of this declaration must be a delegatetype.

An instance of a delegate type encapsulates one or more callable entities. For instance methods, acallable entity consists of an instance and a method on that instance. For static methods, a callable entityconsists of just a method. Given a delegate instance and an appropriate set of arguments, one can invokeall of that delegate instance’s methods with that set of arguments.

In the example

the Button class defines a Click event of type EventHandler. Inside the Button class, the Click member isexactly like a private field of type EventHandler. However, outside the Button class, the Click membercan only be used on the left-hand side of the += and -= operators. The += operator adds a handler for theevent, and the -= operator removes a handler for the event.

Let us take an example, where we have a form and a button on the form. Whenever the button isclicked, that click event has to be identified and message “Button1 was clicked!” must be displayed.

public delegate void EventHandler(object sender, System.EventArgs e);

public class Button{ public event EventHandler Click; public void Reset() { Click = null; }}

using System;

public class Form1{ public Form1() { //Add Button1_Click as event handler for Button1’s Click event Button1.Click += new EventHandler(Button1_Click); }

Button Button1 = new Button();

void Button1_Click(object sender, EventArgs e)



shows a Form1 class that adds Button1_Click as an event handler for Button1’s Click event. In theDisconnect method, that event handler is removed.

For a simple event declaration such as

public event EventHandler Click;

the compiler automatically provides the implementation underlying the += and -= operators.

An implementer who wants more control can get it by explicitly providing add and remove accessors.For example, the Button class could be rewritten as follows:

This change has no effect on calling code, but allows the Button class more implementation flexibility.For example, the event handler for Click need not be represented by a field.

5.7 INDEXERS

An indexer enables an object to be indexed in the same way as an array. Whereas properties enablefield-like access, indexers enable array-like access.

As an example, consider the Stack class presented earlier. The designer of this class might want to usearray like access so that it is possible to manipulate the items on the stack without performing unnecessaryPush and Pop operations. That is, class Stack is implemented as a linked list, but it also provides theconvenience of array access.

{ Console.WriteLine(“Button1 was clicked!”); }

public void Disconnect() { Button1.Click -= new EventHandler(Button1_Click); }}

public class Button{ private EventHandler handler;

public event EventHandler Click { add { handler += value; } remove { handler -= value; } }}

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Indexer declarations are similar to property declarations, with the main differences being that indexersare nameless and that indexers include indexing parameters. The indexing parameters are provided betweensquare brackets. The example

using System;

public class Stack{ private Node GetNode(int index) { Node temp = first; while (index > 0) { temp = temp.Next; index — —; } return temp; }

public object this[int index] { get { if (!ValidIndex(index)) throw new Exception(“Index out of range.”); else return GetNode(index).Value; } set { if (!ValidIndex(index)) throw new Exception(“Index out of range.”); else GetNode(index).Value = value; } } ...}

class Test{ static void Main() { Stack s = new Stack(); s.Push(1); s.Push(2); s.Push(3);



shows an indexer for the Stack class.

5.8 INSTANCE CONSTRUCTORS

An instance constructor is a member that implements the actions required to initialize an instance of aclass.

The example

s[0] = 33; // Changes the top item from 3 to 33 s[1] = 22; // Changes the middle item from 2 to 22 s[2] = 11; // Changes the bottom item from 1 to 11 }}

using System;

class Point{ public double x, y;

// Instance constructor public Point() { this.x = 0; this.y = 0; }

//Parameterized Instance constructor public Point(double x, double y) { this.x = x; this.y = y; }

public static double Distance(Point a, Point b) { double xdiff = a.x - b.x; double ydiff = a.y - b.y; return Math.Sqrt(xdiff * xdiff + ydiff * ydiff); }

public override string ToString() { return string.Format(“({0}, {1})”, x, y); }}

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shows a Point class that provides two public instance constructors, one of which takes no arguments,while the other takes two double arguments.

If no instance constructor is supplied for a class, then an empty one with no parameters is automaticallyprovided.

5.9 DESTRUCTORS

A destructor is a member that implements the actions required to destruct an instance of a class.Destructors cannot have parameters, they cannot have accessibility modifiers, and they cannot be calledexplicitly. The destructor for an instance is called automatically during garbage collection.

The example

shows a Point class with a destructor.

class Test{ static void Main() { Point a = new Point(); Point b = new Point(3, 4); double d = Point.Distance(a, b); Console.WriteLine(“Distance from {0} to {1} is {2}”, a, b, d); }}

using System;

class Point{ public double x, y; public Point(double x, double y) { this.x = x; this.y = y; }

~Point() { Console.WriteLine(“Destructed {0}”, this); }

public override string ToString() { return string.Format(“({0}, {1})”, x, y); }}



5.10 STATIC CONSTRUCTORS

A static constructor is a member that implements the actions required to initialize a class. Staticconstructors cannot have parameters, they cannot have accessibility modifiers, and they cannot be calledexplicitly. The static constructor for a class is called automatically.

The example

shows an Employee class with a static constructor that initializes a static field.

5.11 INHERITANCE

C# classes support single inheritance, and the type object is the ultimate base class for all classes. Theclasses shown in earlier examples all implicitly derive from object.

The example

shows a class ‘A’ that implicitly derives from object. The example

class Employee{ private static DataSet ds; static Employee() { ds = new DataSet(...); }

public string Name; public decimal Salary; ...

}

using System;

class A{ public void F() { Console.WriteLine(“Inside A.F”); }}

class B: A{ public void G() { Console.WriteLine(“Inside B.G”); }}

class Test{

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The output will be

Inside A.F

Inside B.G

Inside A.F

shows a class B that derives from A. The class B inherits A’s F method, and introduces a G method ofits own.

Methods, properties, and indexers can be virtual, which means that their implementation can beoverridden in derived classes. The example

static void Main() { B b = new B(); b.F(); // Inherited from A b.G(); // Introduced in B

A a = b; // Treat a B as an A a.F(); }}

using System;

class A{ public virtual void F() { Console.WriteLine(“A.F”); }}

class B: A{ public override void F() { base.F(); Console.WriteLine(“B.F”); }}

class Test{ static void Main() { B b = new B(); b.F(); A a = b; a.F(); }}



The output will be

shows a class A with a virtual method F, and a class B that overrides F. The overriding method in Bcontains a call, base.F(), which calls the overridden method in A.

A class can indicate that it is incomplete, and is intended only as a base class for other classes, byincluding the modifier abstract. Such a class is called an abstract class. An abstract class can specifyabstract members. These abstract members are members that a non-abstract derived class must implement.The example

The output will be

B.F

B.F

introduces an abstract method F in the abstract class A. The non-abstract class B provides animplementation for this method.

A.FB.FA.FB.F

using System;

abstract class A{ public abstract void F();}

class B: A{ public override void F() { Console.WriteLine(“B.F”); }}

class Test{ static void Main() { B b = new B(); b.F(); A a = b; a.F(); }}

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5.12 METHOD OVERLOADING

Each method has a signature. The signature comprises the method’s name and its parameters but notthe method’s return type. In the following method header, the elements making up the method’s signatureare emphasised. Note also that the ‘params’ keyword is not included in the signature.

public static int myMethod(int a, ref double b, out bool c, params int[] d)

The importance of the signature is that no class is allowed to contain two methods with the samesignature. Since the signature takes in more than the method name, however, it is possible for one class tohave methods sharing a name. For example, a class with the method whose header is given above mightalso contain a method with the header:

public static int myMethod(int a, ref double b)

Note, however, that since neither its return type nor the params keyword are part of a method’ssignature this class could not also contain a method with the header given below:

public static void myMethod(int e,ref double f,out bool g,int[] h)

5.13 OPERATOR OVERLOADING

To overload an operator in a class, one defines a method using the ‘operator’ keyword. For instance,the following code overloads the equality operator

If an operator is one of a logical pair, both operators should be overwritten if any one is overloaded.These pairs are the following:

To understand the need for operator overloading, imagine that we need to perform matrix addition ormultiplication operations in our program. We could instantiate 2 2-dimensional arrays. However, add therequirement for the matrix behavior to be reusable. Because we need to do the same thing in otherprograms and want to take advantage of the fact that we have already written the code, we want tocreate a new type.

So, we create a Matrix type, which could be a class or a struct. We have to initialize two or more

public static bool operator == ( Value a ,Value b){ return a.Int == b.Int}

== and !=< and ><= and >=



Matrix instances with data and then do a mathematical operation with them, such as add or multiply. Toaccomplish the mathematical operation, we implement an Add(), DotProduct(), and other methods to getthe job done. Using the classes would look something like this:

Matrix result = mat1.Add(mat2); // instance

or

Matrix result = Matrix.Add(mat1, mat2); // static

or event worse

Matrix result = mat1.DotProduct(mat2).DotProduct(mat3); // and so on...

The problem with using methods like this is that it is cumbersome, verbose, and unnatural for theproblem we are trying to solve. It would be much easier to have a + operator for the add operation anda * operator for the dot product operation. The following shows how the syntax appears using operators:

Matrix result = mat1 + mat2;

or

Matrix result = mat1 * mat2;

or even better

Matrix result = mat1 * mat2 * mat3 * mat4;

This is much more elegant and easier to work with. For a single operation, one could argue that theamount of work to implement it is not that great. However, for chain of multiple mathematical operations,the syntax is much simpler. Additionally, if the primary users are mathematicians and scientists, operatorsare more intuitive and natural.

Implementing an Overloaded Operator

The syntax required to implement an overloaded operator is much the same as a static method with acouple exceptions. We must use the operator keyword and specify the operator symbol being overloaded. Here is a skeleton example of how the * operator could be implemented:

Notice that the method is static. Use the keyword operator after specifying the return type, Matrix inthis case. Following the operator keyword, the actual operator symbol is specified and then there is a set

public static Matrix operator *(Matrix mat1, Matrix mat2){ // dot product implementation}

88

of parameters to be operated on. Let us see example code of how to implement and use an overloadedoperator.

//Implementing Overloaded Operator

using System;

class Matrix3D{

// its a 3D matrix

public const int DIMSIZE = 3;private double[,] matrix = new double[DIMSIZE, DIMSIZE];

// allow callers to initializepublic double this[int x, int y]{

get { return matrix[x, y]; }set { matrix[x, y] = value; }

}

// let user add matricespublic static Matrix3D operator +(Matrix3D mat1, Matrix3D mat2){

Matrix3D newMatrix = new Matrix3D();

for (int x=0; x < DIMSIZE; x++)for (int y=0; y < DIMSIZE; y++)

newMatrix[x, y] = mat1[x, y] + mat2[x, y];return newMatrix;

}}

class MatrixTest{

// used in the InitMatrix method.public static Random rand = new Random();

// test Matrix3Dstatic void Main(){

Matrix3D mat1 = new Matrix3D();Matrix3D mat2 = new Matrix3D();

// init matrices with random valuesInitMatrix(mat1);InitMatrix(mat2);



// print out matricesConsole.WriteLine(“Matrix 1: “);PrintMatrix(mat1);Console.WriteLine(“Matrix 2: “);PrintMatrix(mat2);

// perform operation and print out resultsMatrix3D mat3 = mat1 + mat2;

Console.WriteLine();Console.WriteLine(“Matrix 1 + Matrix 2 = “);PrintMatrix(mat3);

}

// initialize matrix with random valuespublic static void InitMatrix(Matrix3D mat){

for (int x=0; x < Matrix3D.DIMSIZE; x++)for (int y=0; y < Matrix3D.DIMSIZE; y++)

mat[x, y] = rand.NextDouble()*10;}

// print matrix to consolepublic static void PrintMatrix(Matrix3D mat){

Console.WriteLine();for (int x=0; x < Matrix3D.DIMSIZE; x++){

Console.Write(“[ “);for (int y=0; y < Matrix3D.DIMSIZE; y++){

// format the outputConsole.Write(“{0,8:#.00}”, mat[x, y]);

if ((y+1 % 2) < 3)Console.Write(“, “);

}Console.WriteLine(“ ]”);

}Console.WriteLine();

}}

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The output will be

Similar to the skeleton example of the dot product operator, the Matrix class contains an operatoroverload for the + operator

Operator Rules

C# enforces certain rules when you overload operators. One rule is that you must implement theoperator overload in the type that will use it. This is sensible because it makes the type self-contained.

Another rule is that you must implement matching operators. For example, if you overload ==, youmust also implement !=. The same goes for <= and >=.

When you implement an operator, its compound operator also works. For example, since the + operatorfor the Matrix3D type was implemented, you can also use the += operator on Matrix3D types.

SUMMARY

Classes are reference types. Members of class can be constants, fields, methods, properties, events,indexers, operators, instance constructors, destructors, static constructors, and nested type declarations.There are five forms of accessibility – public, protected, internal, protected internal and private.

A constant represents a constant value and they are initialized at the time of their declaration. A fieldis a member that represents a variable associated with an object or class. Methods can be static or non-static. Static methods are accessed through the class. Non-static methods are accessed through instancesof the class. A property is a member that provides access to a characteristic of an object or a class. Anevent is a member that enables an object to provide notification. An indexer enables an object to be

Matrix 1:

[ 5.40, 9.89, 5.47 ][ 7.08, 4.63, .70 ][ .42, 5.14, 5.96 ]

Matrix 2:

[ 9.95, 8.76, 5.35 ][ 8.42, 4.43, 7.53 ][ 3.57, 7.69, 3.60 ]

Matrix 1 + Matrix 2 =

[ 15.35, 18.66, 10.82 ][ 15.50, 9.07, 8.23 ][ 3.99, 12.83, 9.56 ]



indexed in the same way as an array. An instance constructor is a member that initializes an instance ofa class. A destructor is a member that destructs an instance of a class. A static constructor is a memberthat initializes a class. C# classes support single inheritance, and the System.Object is the ultimate baseclass for all classes. Method and operators can be overloaded in C#.

QUESTIONS

1. Write a note on classes in C#.

2. What are constant members? Give an example.

3. Give an example of field member.

4. With appropriate examples explain parameter passing in C#.

5. What is the use of property member in a class?

6. What are events? Give an example to demonstrate its usage.

7. With an example explain indexers.

8. Explain each with an example

a. Instance constructors

b. Destructor

c. Static constructor

9. How does C# supports inheritance?

10. What is method overloading? Give an example.

11. What is operator overloading? Give an example.

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Chapter 6

Advanced C#


8 Explore C# preprocessor directives

8 Learn how to handle exception

8 Know unsafe code concept

8 Threading

6.1 C# PREPROCESSOR DIRECTIVES

In this section we will discusses about the C# language preprocessor directives. While the compilerdoes not have a separate preprocessor, the directives are processed as if there was a preprocessor.These directives are used during conditional compilation. Unlike C and C++ directives, we cannot use

these directives to create macros. A preprocessor directive must be the only instruction on a line. We willdiscuss about each of them.

#if

#if, begins a conditional directive for testing a symbol, to see if they evaluate to true. If they do

evaluate to true, the compiler evaluates all the code between the #if and the next corresponding directive.

The following operators can also be used to evaluate multiple symbols, like

Chapter 6 - Advanced C#

Chapter 6 - Advanced C#92


== (equality symbol)

!= (inequality symbol)

&& (and symbol)

|| (or symbol)

#if, along with the #else, #elif, #endif, #define, and #undef directives, can be used to include orexclude code based on the condition of one or more symbols. A conditional directive beginning with a #ifdirective must explicitly be terminated with a #endif, directive.

For example,

The output will be,

DEBUG and VC_V6 are defined

#else

#else, creates a compound conditional directive, such that, if none of the expressions in the preceding#if or #elif directives did not evaluate to true, the compiler will evaluate all code between #else and thesubsequent #endif.

#elif

#elif, creates a compound conditional directive, it evaluates if neither the preceding #if nor any preceding

#define DEBUG #define VC_V6 using System; public class MyClass { public static void Main() { #if (DEBUG && !VC_V6) Console.WriteLine("DEBUG is defined"); #elif (!DEBUG && VC_V6) Console.WriteLine("VC_V6 is defined"); #elif (DEBUG && VC_V6) Console.WriteLine("DEBUG and VC_V6 are defined"); #else Console.WriteLine("DEBUG and VC_V6 are not defined"); #endif } }

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#elif directive expressions evaluate to true. If a #elif expression evaluates to true, the compiler evaluatesall the code between the #elif and the next corresponding directive.

#elif is equivalent to using #else and then #if. But using #elif is simpler because each #if requires a#endif, whereas a #elif can be used without a matching #endif.

#endif

#endif specifies the end of a conditional directive, which began with the #if directive.

#define

#define, defines a symbol by using the symbol as the expression passed to the #if directive, the expressionwill evaluate to true.

#undef

#undef, undefines a symbol by using the symbol as the expression in a #if directive, the expression willevaluate to false. The #undef directive must appear in the file before we use any statements that are notdirectives.

For example,

The output will be,

DEBUG is not defined

#warning

#warning, generates a level one warning from a specific location in our code. A common use of#warning is in a conditional directive.

#undef DEBUG using System; public class MyClass { public static void Main() { #if DEBUG Console.WriteLine("DEBUG is defined"); #else Console.WriteLine("DEBUG is not defined"); #endif } }



For example,

#error

#error, generates an error from a specific location in your code. A common use of #error is in aconditional directive.

For example,

#line

#line, modifies the compiler’s line number and the file name output for errors and warnings. A sourcecode file may have any number of #line directives.

For example,

#define DEBUG public class MyClass { public static void Main() { #if DEBUG #warning DEBUG is defined #endif } }

#define DEBUG public class MyClass { public static void Main() { #if DEBUG #error DEBUG is defined #endif } }

public class MyClass2 { public static void Main() { #line 200 int i; // error or warning will be: “CS0168 on line 200” #line 8 char c; // error or warning will be: “CS0168 on line 8” } }

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6.2 EXCEPTION HANDLING

An exception is any error condition or unexpected behavior encountered by a program in execution.Exceptions can be raised because of a fault in our code or in shared library or when operating systemresources not being available or when unexpected conditions the CLR encounters and so on. If theapplication does not handle these exception, then the application terminates (default behavior).

In the .NET Framework, an exception is an object that inherits from the ExceptionClass class. Anexception object is thrown from an area of code where an exception has occurred. If the thrown exceptionis not caught then the application program terminates.

Exceptions in C# provide a structured way of handling both system level and application level errorconditions. The exception mechanism is C# is quite similar to C++ exception handling mechanism, with afew important differences which are:

l In C++, any type value can be used to represent an exception. In C#, all exceptions must berepresented by an instance of a class type derived from System.Exception.

l In C#, a finally block can be used to write termination code which executes in both normalexecution and exceptional conditions. Such code is difficult in C++.

l In C#, system-level exceptions such as overflow, divide-by-zero, and null de-references havewell defined exception.

Here is a C# example, which demonstrates the usage of try, catch, throw and finally statements.using System;using System.IO;

public class ProcessFile{ public static void Main() { try //Opens a text file. {

FileStream fs = new FileStream(“data.txt”, FileMode.Open); StreamReader sr = new StreamReader(fs); string line;

//Read from the file and output it to the console. line = sr.ReadLine(); Console.WriteLine(line); } catch(FileNotFoundException e) { Console.WriteLine(“[Data File Missing] {0}”, e); throw new FileNotFoundException(“data.txt not exists”,e);



} finally { fs.Close(); } }}

If the data.txt file exists then, the out put will be

This is data.txt file

Reached Finally block

If the data.txt file does not exists then, the out put will be

[Data File Missing]

System.IO.FileNotFoundException: Could not find file“E:\Bhagya\CSharpnotes\Program\Programs\bin\Debug\data.txt”.File name: “E:\Bhagya\CSharpnotes\Program\Programs\bin\Debug\data.txt”

at System.IO.__Error.WinIOError(Int32 errorCode, String str)at System.IO.FileStream..ctor(String path, FileMode mode, FileAccess

access,FileShare share, Int32 bufferSize, Boolean useAsync, String msgPath,

Boolean bFromProxy) at System.IO.FileStream..ctor(String path, FileMode mode) at ProcessFile.Main() in

e:\bhagya\CSharpnotes\program\programs\class1.cs:line 10

Throw the exception again

Unhandled Exception: System.IO.FileNotFoundException: data.txt notexists —> System.IO.FileNotFoundException: Could not find file“E:\Bhagya\C Sharp notes\Program\Programs\bin\Debug\data.txt”.

File name:“E:\Bhagya\CSharpnotes\Program\Programs\bin\Debug\data.txt”

at System.IO.__Error.WinIOError(Int32 errorCode, String str)at System.IO.FileStream..ctor(String path, FileMode mode, FileAccess

access,FileShare share, Int32 bufferSize, Boolean useAsync, String msgPath,

Boolean bFromProxy) at System.IO.FileStream..ctor(String path, FileMode mode) at ProcessFile.Main() in

e:\bhagya\CSharpnotes\program\programs\class1.cs:line 10 at ProcessFile.Main() in

e:\bhagya\CSharpnotes\program\programs\class1.cs:line 24

Reached Finally block

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Place the section of code that might throw exceptions in a try block and place code that handlesexceptions in a catch block. The catch block is a series of statements beginning with the keyword catch,followed by an exception type and an action to be taken. We can explicitly throw an exception using thethrow statement. A finally block is always executed, regardless of whether an exception is thrown.

The following example uses a try/catch block to catch a FileNotFoundException. Catch block catchesthe FileNotFoundException and writes a message to the console if the data file is not found. The nextstatement is the throw statement that throws a new FileNotFoundException, which is not handle in further.The text information about the exception is printed on console.

Causes of exceptions

Exception can be thrown in two different following ways.

1. A throw statement throws an exception immediately and unconditionally. Control will not reachthe statement immediately following the throw.

2. Certain exceptional conditions that arise during the processing of C# statements cause anexception in certain circumstances when the operation cannot be completed normally. For example,an integer division operation throws a System.DivideByZeroException if the denominator iszero.

The System.Exception class

The System.Exception is the base class for all exceptions. Few common properties that all exceptionsshare are:

l Message, which is a read-only string that contains a description of the the exception.

l InnerException, is a read-only Exception. If it is a non-null value, it refers to the exception thatcaused the current exception. Otherwise, if value is null, that indicates that this exception wasnot caused by exception.

The value of these properties can be specified in calls to the instance constructor for System.Exception.

How exceptions are handled

Exceptions are handled by a try statement. When an exception occurs, the system searches for thenearest catch block that can handle the exception. Once a matching catch block is found, the control istransferred to the first statement of the catch block and the catch block executes. If no matching catchblock or finally block is found, then the execution of the thread is terminated.

The following exception objects are thrown when corresponding exception occurs.



System.ArithmeticException A base class for exceptions that occur during arithmetic operations, like System.DivideByZeroException and System.OverflowException.

System.ArrayTypeMismatchException Thrown when a store into an array fails because the stored element is incompatible with the actual type of the array.

System.DivideByZeroException Thrown when an attempt to divide an integer value by zero is made.

System.IndexOutOfRangeException Thrown when an attempt to index an array via an index that is less than zero or outside the bounds occurs.

System.InvalidCastException Thrown when an explicit conversion from a base type or interface to a derived types fails at run time.

System.MulticastNotSupportedException Thrown when an attempt to combine two non-null delegates fails, because the delegate type does not have a void return type.

System.NullReferenceException Thrown when a null reference is used in a way that causes the referenced object to be required.

System.OutOfMemoryException Thrown when an attempt to allocate memory (new) fails.

System.OverflowException Thrown when an arithmetic operation in a checked block overflows.

System.StackOverflowException Thrown when the execution stack is exhausted by having too many pending method calls.

System.TypeInitializationException Thrown when a static constructor throws an exception, and no catch block exists to catch it.

Table 6.1 : List of Common Exception Classes

6.3 UNSAFE CODE

The C# language has omitted pointers as a data type. C# instead provides references and the ability to

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create objects that are managed by a garbage collector. This design contributes in making C# a muchsafer language than C or C++. In the core C# language it is simply not possible to have an uninitializedvariable, a “dangling” pointer, or an expression that indexes an array beyond its bounds. These categoriesare main cause of bugs in C and C++ programs, so are eliminated here.

While practically every pointer type construct in C or C++ has a reference type counterpart in C#,there are situations where access to pointer types becomes a necessity. For example, interfacing with theunderlying operating system, accessing a memory-mapped device, or implementing a time-critical algorithmmay not be possible without access to pointers. To address this need, C# provides the ability to writeunsafe code.

In unsafe code it is possible to declare and operate on pointers, to perform conversions betweenpointers and integral types, to take the address of variables, and so forth. In a sense, it is like writing Ccode within a C# program. Unsafe code must be clearly marked with the modifier unsafe, so developerscannot possibly use unsafe features accidentally. When CLR finds this unsafe modifier, the executionengine works to ensure that unsafe code cannot be executed in an untrusted environment.

Unsafe contexts

The unsafe features are available only in unsafe contexts. An unsafe context is introduced by includingan unsafe modifier in the declaration.

l A declaration of a class, struct, interface, or delegate may include an unsafe modifier, in whichcase the entire declaration (including the body of the class, struct, or interface) is considered anunsafe context.

l A declaration of a field, method, property, event, indexer, operator, constructor, destructor, orstatic constructor may include an unsafe modifier, in which case the entire member declarationis considered an unsafe context.

l An unsafe-statement enables the use of an unsafe context within a block. The entire associatedblock is considered an unsafe context.

In the example

the unsafe modifier specified in the struct declaration causes the entire textual struct declaration tobecome an unsafe context. Thus, it is possible to declare the Left and Right fields to be of a pointer type.The example above could also be written

public unsafe struct Node{ public int Value; public Node* Left; public Node* Right;}



public struct Node{ public int Value; public unsafe Node* Left; public unsafe Node* Right;}

Here, the unsafe modifiers in the field declarations cause those declarations to be considered unsafecontexts.

In the below example

the unsafe modifier on the F method in A simply causes the F to become an unsafe context in whichthe unsafe features of the language can be used.

6.4 THREADING

Operating systems use different process space for each process, and processes receive services foroperating system separately. Threads are the basic unit to which an operating system allocates processor

time, and more than one thread can run inside that process. Each thread maintains exception handlers, ascheduling priority, and a set of structures which the system uses to save the thread context until it isscheduled. The thread context includes all of the information the thread needs to resume execution,

including the set of CPU registers and stack, in the address space of the thread’s host process.

When To Use Multiple Threads

Software that requires user interaction must react to the user’s requests rapidly to provide a userfriendly experience. At the same time, however, it must do the calculations necessary to respond to the

user as fast as possible. If application uses only one thread of execution, then it may be difficult to processall the request simultaneously and decrease the data processing time of application. In such cases multiplethreads can be created to do the bits of work independently to increase application’s responsiveness.

Advantages of Multiple Threads

Using more than one thread, however, is the most powerful technique available to increase user

public class A{ public unsafe virtual void F() { char* p; ... }}

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responsiveness and process the data necessary to get the work done at almost the same time. On acomputer with one processor, multiple threads can create this effect, taking advantage of the small periodsof time in between user’s IO events to process the data in the background. For example, a user can edita spreadsheet while another thread is recalculating other parts of the spreadsheet within the same application.

Without modification, the same application would dramatically increase user satisfaction when run ona computer with more than one processor. Your single application domain could use multiple threads toaccomplish the following tasks:

l Communicate over a network, to a Web server and to a database.

l Perform operations that take a large amount of time.

l Distinguish tasks of varying priority. For example, a high-priority thread manages time-criticaltasks, and a low-priority thread performs other tasks.

l Allow the user interface to remain responsive, while allocating time to background tasks.

Disadvantages of Multiple Threads

Threading also has resource requirements and potential conflicts, which should be considered whendesigning your application. It is good to use as few threads as possible. The resource requirements forthread are as follows:

l Memory requirement for the context information required by processes, Application Domainobjects, and threads. Therefore, the number of processes, Application Domain objects, andthreads which can be created is limited by memory availability.

l Keeping track of a large number of threads consumes significant processor time. If there aretoo many threads, then there will not be any significant advantage of threads.

l Controlling execution of an application with many threads can be a source of many bugs and itis very complex.

Examples on Threads Usage

The example given in this section demonstrates how to create and start a thread. It shows the interactionbetween two threads running simultaneously within the same process. Note that we don’t have to stop orfree the thread. This is done automatically by the .NET Framework common language runtime.

The program begins by creating an object of type A (oA) and a thread (oThread) that references theB method of the A class. The thread is then started. The IsAlive property of the thread allows theprogram to wait until the thread is initialized (created, allocated, and so on). The main thread is accessedthrough Thread, and the Sleep method tells the thread to give up its time slice and stop executing for acertain amount of milliseconds. The oThread is then stopped and joined. Joining a thread makes the main



thread wait for it to die or for a specified time to. Finally, the program attempts to restart oThread, but failsbecause a thread cannot be restarted after it is stopped (aborted).

using System;using System.Threading;public class A{ // This method that will be called when the thread is started public void B() { while (true) { Console.WriteLine(“A.B is running in its own thread.”); } }};

public class Simple{ public static int Main() { Console.WriteLine(“Thread Start/Stop/Join Example”);

A oA = new A();

// Create the thread object, passing in the A.B method // via a ThreadStart delegate. This does not start the thread. Thread oThread = new Thread(new ThreadStart(oA.B));

// Start the thread oThread.Start();

// loop until the started thread becomes alive while (!oThread.IsAlive);

// Main thread sleeps for 1 ms untill oThread finishes its work Thread.Sleep(1);

// oThread is stopped oThread.Abort();

// Wait until oThread finishes and Joins. oThread.Join();

Console.WriteLine(); Console.WriteLine(“A.B has finished”);

try

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{ Console.WriteLine(“Try to restart the A.B thread”); oThread.Start(); } catch (ThreadStateException) { Console.Write(“ThreadStateException trying to restart A.B”); Console.WriteLine(“Aborted threads cannot be restarted.”); } return 0; }}

The Output will be

Pausing and Resuming Threads

After a thread has started, it can often pause thread for a fixed period of time. Calling Thread.Sleepcauses the current thread to immediately block for the specified number of milliseconds, yielding theremainder of its time slice to another thread. One thread cannot call Sleep on another thread. CallingThread.Sleep(Timeout.Infinite) causes a thread to sleep until it is interrupted by another thread that callsThread.Interrupt or is aborted by Thread.Abort.

A thread can also be paused by calling Thread.Suspend. When a thread calls Thread.Suspend onitself, the call blocks until the thread is resumed by another thread. When one thread calls Thread.Suspendon another thread, the call is a nonblocking call that causes the other thread to pause. Calling Thread.Resumebreaks another thread out of the suspend state and causes the thread to resume execution, regardless ofhow many times Thread.Suspend was called. For example, if you call Thread.Suspend five consecutivetimes and then call Thread.Resume, the thread will resume execution immediately following the call toResume.

Unlike Thread.Sleep, Thread.Suspend does not cause a thread to immediately stop execution. Thecommon language runtime must wait until the thread has reached a safe point before it can suspend thethread. A thread cannot be suspended if it has not been started or if it has stopped.

The Suspend and Resume methods are not generally useful for applications. It should not be confused

Thread Start/Stop/Join ExampleA.B is running in its own thread.A.B is running in its own thread.A.B is running in its own thread.......A.B has finishedTry to restart the A.B threadThreadStateException trying to restart A.BAborted threads cannot be restarted.



with synchronization mechanisms, because Suspend and Resume do not rely on the cooperation of thethread being controlled. They are highly intrusive and can result in serious application problems likedeadlocks (for example, if you suspend a thread that holds a resource that another thread will need).

Some applications do need to control the priority of threads for better performance. To do this, you shoulduse Thread.Priority rather than Thread.Suspend.

A thread can be blocked in a number of ways. For example, we can have a thread wait for another

thread to stop by calling Thread.Join. We can have a thread wait for access to a synchronized object usingMonitor.Wait, or we can put it to sleep using Thread.Sleep. We can interrupt a waiting thread by callingThread.Interrupt on the blocked thread to throw a ThreadInterruptedException, which breaks the thread

out of the blocking call. The thread should catch the ThreadInterruptedException and do whatever isappropriate to continue working. If the thread ignores the exception, the runtime catches the exceptionand stops the thread.

If a thread is in wait, then Thread.Interrupt and Thread.Abort both wake the thread immediately.

Thread.Interrupt wakes a thread out of any wait it might be in and causes a ThreadInterruptedExceptionto be thrown in the destination thread. Thread.Abort is similar to Thread.Interrupt, except that it throwsthe ThreadAbortException. This is a special exception that cannot be caught from managed code.

Destroying Threads

The Thread.Abort method is used to stop a logical thread permanently. When we call Abort, thecommon language runtime throws a ThreadAbortException. The thread can catch the exception, butcannot suppress it. The runtime will execute the catch block and any finally block.

Because Thread.Abort does not cause the thread to abort immediately, we must call Thread.Join to

wait on the thread to be sure the thread is stopped. Join is a blocking call that does not return until thethread has actually stopped executing. Once a thread is aborted, it cannot be restarted.

Thread.Join can also be called and passed a time-out period. If the thread dies before the time out has

elapsed, the call returns true. Otherwise, if the time expires before the thread dies, the call returns false.Threads that are waiting on a call to Thread.Join can be interrupted by other threads that callThread.Interrupt.

A ThreadAbortException can occur anywhere in managed code. However, they only occur if a

privileged thread calls Thread.Abort. The best way to handle them is to have adequate finally or catchblock to maintain consistent state. The privileged code that provokes the ThreadAbortException willcatch it and reset it if necessary.

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6.5 LIBRARY BASE CLASSES

The .NET Framework base classes include classes, interfaces, and value types that provide access tosystem functionality. To facilitate interoperability between languages, the .NET Framework base classesare CLS compliant and therefore can be used from any programming language.

The .NET Framework library base classes are the foundation on which .NET applications, components,and controls are built. These also include types that perform the following functions:

l Represent base data types and exceptions.

l Encapsulate data structures.

l I/O operations

l Access information of types.

l .NET Framework security checks.

l Provide data access, GUI, and Web services.

The .NET Framework provides a rich set of interfaces, abstract and concrete (non-abstract) classes.We can use the concrete classes as is or can derive own classes from them. To use the functionality of aninterface, we can either create a class that implements the interface or derive a class from one of theinterface of .NET Framework classes.

Naming Conventions

.NET Framework types use a dot (.) syntax naming scheme that is in a hierarchy. This techniquegroups related types into namespaces so, they can be searched and referenced easily. The first part of thefull name, up to the rightmost dot, is the namespace name. The last part of the full name is the type name.For example, System.Collections.ArrayList represents the ArrayList type, which belongs to theSystem.Collections namespace. The types in System.Collections can be used to manipulate collections ofobjects.

The System namespace is the root namespace for fundamental types in the .NET Framework. Thisnamespace includes classes that represent the base data types like Object (the root of the inheritancehierarchy), Byte, Char, Array, Int32, String, and so on. Many of these types correspond to the primitivedata types that our programming language uses. When we write code using .NET Framework types, wecan use our language’s corresponding keyword when a .NET Framework base data type is expected.

The following table lists some of the value types the .NET Framework supplies, briefly describesthem. It indicates the corresponding type in VisualBasic.NET, C#, and the Managed C++.



Category Class name Description

Visual Basic. NET

C# Managed

C++ JScript

Integer Byte An 8-bit unsigned integer. Byte byte Char byte

SByte An 8-bit signed integer.

Not CLS compliant.

SByte

No built-in type.

sbyte Signed char

SByte

Int16 A 16-bit signed integer. Short short Short short Int32 A 32-bit signed integer. Integer int int ,long int Int64 A 64-bit signed integer. Long long __int64 long

UInt16 A 16-bit unsigned integer.

Not CLS compliant.

UInt16

No built-in type.

ushort unsigned short

UInt16


Not CLS compliant.

UInt32

No built-in type.

uint

unsigned int , unsigned long

UInt32


Not CLS compliant.

UInt64

No built-in type.

ulong unsigned __int64

UInt64

Floating point

Single A single-precision (32-bit) floating-point number.

Single float float float

Double A double-precision (64-bit) floating-point number.

Double double double double

Logical Boolean A Boolean value (true or false).

Boolean bool bool bool

Other Char A Unicode (16-bit) character.

Char char wchar_t char

Decimal A 96-bit decimal value. Decimal decimal Decimal Decimal

IntPtr

A signed integer whose size depends on the underlying platform (a 32-bit value on a 32-bit platform and a 64-bit value on a 64-bit platform).

IntPtr

No built-in type.

IntPtr

No built-in type.

IntPtr

No built-in type.

IntPtr

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UIntPtr

An unsigned integer whose size depends on the underlying platform (a 32- bit value on a 32-bit platform and a 64-bit value on a 64-bit platform).

Not CLS compliant.

UIntPtr

No built-in type.

UIntPtr

No built-in type.

UIntPtr

No built-in type.

UIntPtr

Class objects

Object The root of the object hierarchy.

Object object Object* Object

String An immutable, fixed-length string of Unicode characters.

String string String* String

Table 6.2 : .NET Framework value types

In addition to the base data types, the System namespace contains almost 100 classes, ranging fromclasses that handle exceptions to classes that deal with application domains and the garbage collector.

6.5.1 System.Object

System.Object class is the ultimate base class that all types directly or indirectly derive from. Theobject class allows us to build generic routines, provides Type System Unification, and enables workingwith groups collections. Commonly generic routines must accept arguments of type object and allowusers to pass any type they want. This approach of generic routines is difficult to maintain because of thelack of type safety and inefficiency for value types. Generics in C# will replace the practice of using theobject class for generic routines.

Reference types inherit the object class either directly or through other reference types. Value typesinherit implicitly from object class through System.ValueType. In C#, the object class is a languagespecific with the fully qualified name of System.Object.

The ability of both reference types and value types to be treated as objects supports Common TypeSystem. In many languages, built-in types such as int and float have no object-oriented properties andmust be explicitly wrapped in objects to simulate object-oriented behavior. However, C# eliminates therequirement to wrap built-in types. Value types inherit from System.ValueType, which inherits fromSystem.Object. This allows C# built-in types to be worked in a manner similar to reference types. Froman object-oriented perspective, under Common Type System both reference types and value types areobjects.

Of course we do not get Common Type System for free. When assigning a value type to an object, in



the background, the system performs an extra operation referred to as Boxing. After a boxing operationhas completed, a value type is considered boxed. Similarly, when copying a boxed value type back to anormal value type, in the background, the system performs another operation referred to as Unboxing. While any value type can be boxed, it is not logical to assume that any reference type can be unboxed. Onlyobjects that are previously boxed can be unboxed. When a value type is boxed, a new object for that typeis created in memory and the value is copied into that object. During unboxing the value in the object iscopied into the value of a value type. The below piece of code shows a simple boxing/unboxing operation.

Although for performance reasons, we need to be aware of the boxing/unboxing operations. Thisconcept makes it very simple to work with all types in the same manner for those times when suchbehavior in our application is necessary.

The object class also facilitates using any type in a collection. It contains methods that can be reusedor overridden in base types. Since collections, such as Hashtable and ArrayList accept object types, wecan add any type to them. The Equals, GetType, and GetHashCode object class methods are calleddirectly by the collection classes. Other object class methods offer general capabilities that types haveaccess to and can expose in their interface.

The Equals Method

This is a common operation, especially for searching and sorting in collections, it tests two objects forequality. The Equals method of the object class provides a default implementation that compares tworeference type objects for reference equality. Reference equality occurs when two reference type objectsrefer to the same object. Sometimes reference types need to define value equality instead of referenceequality. Fortunately, the Equals method is virtual, so derived reference types may override it. An exampleis the string class, which overrides Equals to ensure that two strings are compared by the value of theirstrings. Value types are compared for bitwise equality. The below code demonstrates how to use theEquals method with reference types.

int myValueType1 = 8;

object myReferenceType = myValueType1; // myValueType is boxed

int myValueType2 = (int) myReferenceType; // myValueType is unboxed

using System;class Employee{ string e_name; public Employee(string name) { e_name = name; }}

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class EqualsDemonstration{ static void Main() { EqualsDemonstration eqDemo = new EqualsDemonstration(); eqDemo.InstanceEqual(); Console.ReadLine(); }

public void InstanceEqual() { string name = “Joe”; Employee employee1 = new Employee(name); Employee employee2 = new Employee(name);

// comparing references of separate instances bool isEqual = employee1.Equals(employee2);

Console.WriteLine(“employee1 == employee2 - {0}”, isEqual);

employee2 = employee1;

// comparing references of the same instance isEqual = employee1.Equals(employee2);

Console.WriteLine(“employee1 == employee2 - {0}”, isEqual); }}

The output will be

employee1 == employee2 - Falseemployee1 == employee2 - True

The above code shows how the default implementation of Equals in the object class performs comparisonon reference types. In the InstanceEqual method the first comparison is of two separate instances ofEmployee, so the result of the call to Equals will be false. Next, the reference to the object that employee1refers to is assigned to employee2, making both references refer to the same instance. This makes thenext call to the Equals method return true. To change the way Equals works, the Employee class couldoverride Equals and provide an implementation based on equality of the e_name member.

There is also a static Equals method that performs the same task: Object.Equals(object obj1,object obj2).

The ReferenceEquals Method

In the object class, the Equals and ReferenceEquals methods are semantically equivalent, except



that the ReferenceEquals works only on object instances. The ReferenceEquals method is static. Thebelow program demonstrates how to use the ReferenceEquals method.

using System;class Employee{ string e_name;

public Employee(string name) { e_name = name; }}

class ReferenceEqualsDemo{ static void Main() { ReferenceEqualsDemo refEqDem = new ReferenceEqualsDemo();

refEqDem.InstanceEqual();

Console.ReadLine(); }

public void InstanceEqual() { string name = “Joe”;

Employee employee1 = new Employee(name); Employee employee2 = new Employee(name);

// comparing separate instances bool isEqual = Object.ReferenceEquals(employee1, employee2);

Console.WriteLine(“employee1 == employee2 - {0}”, isEqual);

employee2 = employee1;

// comparing the same instance isEqual = Object.ReferenceEquals(employee1, employee2); Console.WriteLine(“employee1 == employee2 - {0}”, isEqual); }}

The output will be

employee1 == employee2 - Falseemployee1 == employee2 - True

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Notice that the previous both code are the same except that second one uses the ReferenceEqualsmethod. The results are also the same.

The ToString Method

The purpose of the ToString method is to return a string representation of a type. The defaultimplementation in the object class returns a string with the name of the object. The below given piece ofcode demonstrates how to implement the ToString method in our own type.


public Employee(string name) { e_name = name; }

// If ToString() is not overridden, the output of this program willbe “Employee”.

public override string ToString() { return String.Format(“[Employee: {0}]”, e_name); }}

class ToStringDemonstration{ static void Main() { Employee emp = new Employee(“Joe”);

Console.WriteLine(emp.ToString());

Console.ReadLine(); }}The output will be

[Employee: Joe]

The ToString method overrides ToString in the object class. We can use ToString to facilitate debuggingby providing human readable information about our type that can be viewed by developers inspectingprogram output emitted by calls to the ToString method.

The GetType Method

GetType is the basis for using reflection in .NET. It returns a Type object, describing the object it was



called on. It can then be used to extract type member data like methods and fields that may subsequentlybe used for late-bound method invocations. The GetType method is also useful if we get an object atruntime and we do not know what its type is. We can use the returned Type object to figure out what todo with the object. Below listed code demonstrates how to use the GetType method.

The output will be

There are two instances of the Employee class created in the Main method. The first is assigned to areference of type object and the second is assigned to a reference of type Employee. When we run, theprogram will print “Employee” as the result of the call to GetType. This shows that GetType returns therun-time type of the object it is called on, rather than the compile-time reference it is assigned to.

The GetHashCode Method

The GetHashCode method makes any object usable in a Hashtable or any hashing algorithm. Sincethe default algorithm supplied by the GetHashCode method of the object class is not guaranteed to beunique, we should override GetHashCode in our custom types. Below listing demonstrates how toimplement a custom GetHashCode method.

using System;class Employee{}

class GetTypeDemonstration{ static void Main() { object emp1 = new Employee(); Employee emp2 = new Employee();

Console.WriteLine(emp1.GetType()); Console.WriteLine(emp2.GetType());

Console.ReadLine(); }}

EmployeeEmployee


public Employee(string name) {

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e_name = name; }

public override int GetHashCode() { string uniqueString = ToString();

return uniqueString.GetHashCode(); }

public override string ToString() { return String.Format(“[Employee: {0}]”, e_name); }}

class GetHashCodeDemonstration{ static void Main() { Employee emp = new Employee(“Joe”);

Console.WriteLine(emp.GetHashCode());

Console.ReadLine(); }}

The output will be

The Employee class overrides the GetHashCode method to provide a unique number for each uniqueinstance of the Employee class. This is accomplished by using the ToString method that will return astring uniquely representing the value of this instance. Then GetHashCode is called on the string andreturned to the caller. The benefits of using the string class are that it already has a GetHashCodefunction that can be used. The GetHashCode method of the string class returns a random distribution ofhash codes, guarantees codes are unique for different strings, and ensures codes are identical for thesame strings.

The MemberwiseClone Method

Whenever we need to create a bitwise copy (shallow copy) of our type, the MemberwiseClonemethod is used. As such, if we perform a MemberwiseClone on our class, it will make a copy of the typeand all contained value types and references types. However, it will not copy the objects that the referencetype members in our type refer to. This behavior of only making a copy of the first level of our type tells

-275241189



the reason why a MemberwiseClone is called a shallow copy. Since the MemberwiseClone method isnot virtual, we can not override it in derived classes. Program below shows how to use MemberwiseClone.

using System;public class Address{ }class Employee{ Address e_address = new Address(); string e_name;

public Employee(string name) { e_name = name; }

public Employee ShallowCopy() { return (Employee)MemberwiseClone(); }

public Address EmployeeAddress { get { return e_address; } }}

class MemberwiseCloneDemonstration{ static void Main() { Employee emp1 = new Employee(“Joe”); Employee emp2 = emp1.ShallowCopy();

// compare Employee references bool isEqual = Object.ReferenceEquals(emp1, emp2); Console.WriteLine(“emp1 == emp2 - {0}”, isEqual);

//compare reference of Address object in each Employee object isEqual = Object.ReferenceEquals(emp1.EmployeeAddress,emp2.EmployeeAddress);

Console.WriteLine(“emp1.EmployeeAddress == emp2.EmployeeAddress -{0}”, isEqual); Console.ReadLine(); }}

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The output will be

emp1 == emp2 - Falseemp1.EmployeeAddress == emp2.EmployeeAddress – True

Since MemberwiseClone has protected visibility, wraps the call to it in the ShallowCopy method of theEmployee class. When the Main method calls ShallowCopy, the emp2 variable holds a reference to acopy of emp1. However, this is a shallow copy, as subsequent statements prove. The first call toReferenceEquals shows that the emp1 and emp2 variables refer to separate instances. The second call toReferenceEquals performs a comparison on the Address object within the emp1 and emp2 instances. Thecomparison demonstrates that both of the Address references point to the same object, proving that onlya shallow copy has been performed.

The Finalize Method

Although the object class has a Finalize method, it is not available to C# programs in that form. Instead,we can use what is called a destructor in C#, which is synonymous with the Finalize method. In furtherdiscussion, we will refer to the Finalize method as a destructor. The original purpose of the destructorwas to serve as a place where we can release unmanaged resources such as network connections,operating system resources, or file streams. However, in practice we never want to use the destructor. Thereason is that a destructor is executed automatically by the garbage collector. Developers familiar withC++ will notice that this is a distinct difference in destructor behavior because in C++ a destructor isexecuted deterministically, as soon as an object is freed. The solution to this problem in C# is to implementthe IDisposable interface on all our types that need to release unmanaged resources. Below programshows a class that implements a destructor.

using System;class Employee{

string e_name;

public Employee(string name){

e_name = name;Console.WriteLine(“Employee Name: {0}”, e_name);

}

~Employee(){

Console.WriteLine(“Employee destructor executed.”);}

}

class DestructorDemonstration{

static void Main()



{Employee emp = new Employee(“Joe”);

}}

The output will be

The Employee class implements a destructor. Destructors are prefixed with a (∼) tilde and named thesame as their containing class. Additionally, they do not have parameters. Value types do not havedestructors. If we run this program it will print employees name to the console and then executes thedestructor. Since it is so small, it will not consume enough memory resources to force a garbage collection,which in turn would call the destructor. If the program was holding an unmanaged resource, the unmanagedresource would not be released. When employees name is printed to the console, the CLR will initiate agarbage collection and the program will print “Employee destructor executed.” to the screen when thegarbage collector calls the destructor, prior to final program shutdown.

6.5.2 String Handling

In C#, a text string is stored in a data type named string, which is an alias to the System.String type. Inother words, when we create a string, we instantiate a System.String object.

In addition to its instance members, the System.String class has quite a few important static methods.These methods do not require a string instance to work.

It is important to understand that the string type is immutable. This means that once it has beencreated, a string cannot be changed. No characters can be added or removed from it, nor can its length bechanged.

But let us have a look at below piece of code

Well, here set of statements actually create a new instance of the variable str each time a value isassigned to str. In other words, in this example, an instance of str has been created, and a literal stringvalue assigned to it three times. The statement that the type is immutable means that an instance cannotbe edited but it can be assigned.

Employee Name: JoeEmployee destructor executed.

string str = “I am going to have a lot of fun”;str += “ with Dudley this summer. ... “;str += “ The End”;

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Using an instance method without an assignment is syntactically legal, but it does not do anything i.e.,it has no effect. For example

does not change the contents of the variable str, although combining it with an assignment would work:

Now the new value of str is, of course, “heLLo”.

It is easy enough to use assignments when we need to change the value of string. But instantiating anddestroying strings every time will result in negative performance consequences. If performance is anissue, we should consider working with instances of the System.Text.StringBuilder class, which are mutable(can be changed).

Once created, a string has a specific length, which is fixed. A C# string is not a terminated array ofcharacters (unlike in the C language, in which a string is simply an array of characters terminated with azero byte). So, how does one determine the length of a C# string? The length of C# string can be knownby querying the read-only Length property of the string instance. For example

Len = str.Length;

gives the length of string ‘str’.

6.5.3 Arrays

An array is a data structure that contains a number of variables called the elements of the array. Thearray elements are accessed through indexes. C# arrays are zero indexed; that is, the array indexes startat zero. All of the array elements must be of the same type. Array elements can be of any type, includingan array type. An array can be a single-dimensional array, or a multidimensional array. Array types arereference types derived from the abstract base type System.Array.

We will discuss the following topics one by one

l Single-Dimensional Arrays

l Multidimensional Arrays

l Jagged Arrays

l Passing Arrays Using ref and out

string str = “hello”;

str.Replace (“l”, “L”); // Does not do anything

string str = “hello”;str = str.Replace (“l”, “L”);



6.5.3.1 Single-Dimensional Arrays

We can declare an array of five integers as in the following example:

This array contains the elements from myArray[0] to myArray[4]. The new operator is used to createthe array and initialize the array elements to their default values. In this case, all the array elements areinitialized to zero.

An array that stores string elements can be declared in the same way. For example:

Array Initialization

It is possible to initialize an array upon declaration. The number of elements of the array is not neededto be specified because it is already supplied by the number of elements in the initialization list. Forexample:

A string array can be initialized in the same way. The following is a declaration of a string array whereeach array element is initialized by a name of a day.

When we initialize an array upon declaration, it is possible to use the following shortcuts:

It is possible to declare an array variable without initialization, but we must use the new operator whenwe assign an array to this variable. For example:

Value Type and Reference Type Arrays

Consider the following array declaration:

int[] myArray = new int [5];

string[] myStringArray = new string[6];

int[] myArray = new int[] {1, 3, 5, 7, 9};

string[] weekDays = new string[] {“Sun”,”Sat”,”Mon”,”Tue”,”Wed”,”Thu”,”Fri”};

int[] myArray = {1, 3, 5, 7, 9};string[] weekDays = {“Sun”,”Sat”,”Mon”,”Tue”,”Wed”,”Thu”,”Fri”};

int[] myArray;myArray = new int[] {1, 3, 5, 7, 9}; // OKmyArray = {1, 3, 5, 7, 9}; // Error

MyType[] myArray = new MyType[10];

120

The result of this statement depends on whether MyType is a value type or a reference type. If it is avalue type, the statement results in creating an array of 10 instances of the type MyType. If MyType is areference type, the statement creates an array of 10 elements, each of which is initialized to a nullreference.

Passing Arrays as Parameters

We can pass an initialized array to a method. For example:

We can also initialize and pass a new array in one step. For example:

PrintArray(myArray);

PrintArray(new int[] {1, 3, 5, 7, 9});

In the following example, a string array is initialized and passed as a parameter to the PrintArraymethod, where its elements are displayed:

using System;

public class ArrayClass{ static void PrintArray(string[] s) { for (int i = 0 ; i < s.Length ; i++) Console.Write(s[i] + “{0}”, i < s.Length - 1 ? “ “ : “”); Console.WriteLine(); }

public static void Main() { // Declare and initialize an array: string[] WeekDays = new string [] {“Sun”,”Sat”,”Mon”,”Tue”,”Wed”,”Thu”,”Fri”};

// Pass the array as a parameter: PrintArray(WeekDays); }}

The output will be

Sun Sat Mon Tue Wed Thu Fri



6.5.3.2 Multidimensional Arrays

Arrays can have more than one dimension. For example, the following declaration creates a two-dimensional array of four rows and two columns:

Also it can create an array of three dimensions, 4, 2, and 3, as show below:

Array Initialization

We can initialize the array upon declaration as shown in the following example:

We can also initialize the array without specifying the rank (number of elements):

If we choose to declare an array variable without initialization, we must use the ‘new’ operator toassign an array to the variable. For example:

We can also assign a value to an array element, for example:

Passing Arrays as Parameters

We can pass an initialized array to a method. For example:

we can also initialize and pass a new array in one step. For example:

In this example, a two-dimensional array is initialized and passed to the PrintArray method, where itselements are displayed.

int[,] myArray = new int[4,2];

int[,,] myArray = new int [4,2,3];

int[,] myArray = new int[,] {{1,2}, {3,4}, {5,6}, {7,8}};

int[,] myArray = {{1,2}, {3,4}, {5,6}, {7,8}};

int[,] myArray;myArray = new int[,] {{1,2}, {3,4}, {5,6}, {7,8}}; // OKmyArray = {{1,2}, {3,4}, {5,6}, {7,8}}; // Error

myArray[2,1] = 25;

PrintArray(myArray);

PrintArray(new int[,] {{1,2}, {3,4}, {5,6}, {7,8}});

122

using System;public class ArrayClass{ static void PrintArray(int[,] s) { // Display the array elements: for (int i=0; i < 4; i++) for (int j=0; j < 2; j++) Console.WriteLine(“Element({0},{1})={2}”,i,j,s[i,j]); }

public static void Main() { // Pass the array as a parameter: PrintArray(new int[,] {{1,2}, {3,4}, {5,6}, {7,8}}); }}

The output will be

Element(0,0)=1Element(0,1)=2Element(1,0)=3Element(1,1)=4Element(2,0)=5Element(2,1)=6Element(3,0)=7Element(3,1)=8

6.5.3.3 Jagged Arrays

A jagged array is an array whose elements are arrays. The elements of a jagged array can be ofdifferent dimensions and sizes. A jagged array is sometimes called an “array-of-arrays.” This we will seeexamples of declaring, initializing, and accessing jagged arrays.

The following is a declaration of a single-dimensional array that has three elements, each of which isa single-dimensional array of integers:

Before we can use myJaggedArray, its elements must be initialized. We can initialize the elements like:

int[][] myJaggedArray = new int[3][];

myJaggedArray[0] = new int[5];myJaggedArray[1] = new int[4];myJaggedArray[2] = new int[2];



Each of the elements is a single-dimensional array of integers. The first element is an array of 5integers, the second is an array of 4 integers, and the third is an array of 2 integers.

It is also possible to use initializers to fill the array elements with values, in which case we do not needthe array size, for example:

We can also initialize the array upon declaration like this:

We can use the following shortcut. Notice that we cannot omit the new operator from the elementsinitialization because there is no default initialization for the elements.

We can access individual array elements like these examples:

It is possible to mix jagged and multidimensional arrays. The following is a declaration and initializationof a single-dimensional jagged array that contains two-dimensional array elements of different sizes:

We can access individual elements like this example, which displays the value of the element [1,0] ofthe first array (value 5):

myJaggedArray[0] = new int[] {1,3,5,7,9};myJaggedArray[1] = new int[] {0,2,4,6};myJaggedArray[2] = new int[] {11,22};

int[][] myJaggedArray = new int [][] { new int[] {1,3,5,7,9}, new int[] {0,2,4,6}, new int[] {11,22} };

int[][] myJaggedArray = { new int[] {1,3,5,7,9}, new int[] {0,2,4,6}, new int[] {11,22} };

// Assign 33 to the second element of the first array:myJaggedArray[0][1] = 33;

// Assign 44 to the second element of the third array:myJaggedArray[2][1] = 44;

int[][,] myJaggedArray = new int [3][,] { new int[,] { {1,3}, {5,7} }, new int[,] { {0,2}, {4,6}, {8,10} }, new int[,] { {11,22}, {99,88}, {0,9} } };

124

This example builds an array, myArray, whose elements are arrays. Each one of the array elementshas a different size.

The output will be

6.5.3.4 Passing Arrays Using ref and out

Like all out parameters, an out parameter of an array type must be assigned before it is used; that is,it must be assigned by the callee.

For example:

Console.Write(“{0}”, myJaggedArray[0][1,0]);

using System;public class JaggedArrayDemonstration{ public static void Main() { // Declare the Jagged array of two elements: int[][] myArray = new int[2][];

// Initialize the elements: myArray[0] = new int[5] {1,3,5,7,9}; myArray[1] = new int[4] {2,4,6,8};

// Display the array elements: for (int i=0; i < myArray.Length; i++) { Console.Write(“Element({0}): “, i);

for (int j = 0 ; j < myArray[i].Length ; j++) Console.Write(“{0}{1}”, myArray[i][j], j == (myArray[i].Length-1) ? “” : “ “);

Console.WriteLine(); } }}

Element(0): 1 3 5 7 9Element(1): 2 4 6 8



Like all ref parameters, a ref parameter of an array type must be definitely assigned by the caller.Therefore, there is no need to be definitely assigned by the callee. A ref parameter of an array type maybe altered as a result of the call. For example, the array can be assigned the null value or can be initializedto a different array.

For example:

The following two examples demonstrate the difference between out and ref when used in passingarrays to methods.

Example 1

In this example, the array myArray is declared in the caller (the Main method), and initialized in theFillArray method. Then, the array elements are returned to the caller and displayed.

public static void MyMethod(out int[] arr){ arr = new int[10]; // definite assignment of arr}

public static void MyMethod(ref int[] arr){ arr = new int[10]; // arr initialized to a different array}

using System;class TestOut{ static public void FillArray(out int[] myArray) { // Initialize the array: myArray = new int[5] {1, 2, 3, 4, 5}; }

static public void Main() { int[] myArray; // Initialization is not required

// Pass the array to the callee using out: FillArray(out myArray);

// Display the array elements: Console.WriteLine(“Array elements are:”); for (int i=0; i < myArray.Length; i++) Console.WriteLine(myArray[i]); }}

126

The output will be

Example 2

In this example, the array myArray is initialized in the caller (the Main method), and passed to theFillArray method by using the ref parameter. Some of the array elements are updated in the FillArraymethod. Then, the array elements are returned to the caller and displayed.

The output will be

Array elements are:12345

using System;

class TestRef{ public static void FillArray(ref int[] arr) { // Create the array if (arr == null) arr = new int[10]; // Otherwise fill the array: arr[0] = 123; arr[4] = 1024; }

static public void Main () { // Initialize the array: int[] myArray = {1,2,3,4,5};

// Pass the array using ref: FillArray(ref myArray);

// Display the updated array: Console.WriteLine(“Array elements are:”); for (int i = 0; i < myArray.Length; i++) Console.WriteLine(myArray[i]); }}



Array elements are:1232341024

6.5.4 System.Collections

The System.Collections namespace contains interfaces and classes that define various collectionsof objects, such as lists, queues, bit arrays, hashtables and dictionaries.

Each class has a set of methods and properties, which are used on those corresponding class objects.

Class Description

ArrayList The IList interface (to implement list) is used, in which an array whose size is dynamically increased as required.

BitArray Manages a compact array of bit values, which are represented as Booleans.

CaseInsensitiveComparer Compares two objects for equivalence. The case of the string is ignored while comparing.

CaseInsensitiveHashCodeProvider Supplies a hash code for an object, using a hashing algorithm. The case of the string is ignored.

CollectionBase Provides the abstract base class for a strongly typed collection.

Comparer Compares two objects for equivalence, where string comparisons are case-sensitive.

DictionaryBase Provides the abstract base class for a strongly typed collection of key-and-value pairs.

Hashtable Represents a collection of key-and-value pairs that are organized based on the hash code of the key.

Queue Represents a FIFO collection of objects.

ReadOnlyCollectionBase Provides the abstract base class for a strongly typed read-only collection.

SortedList Represents a collection of key-and-value pairs that are sorted by the keys and are accessible by key and by index.

Stack Represents a simple LIFO collection of objects.

Table 6.4 : Lists the important classes of System.Collection

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SUMMARY

C# compiler does not have a separate preprocessor; the directives are processed as if there was a

preprocessor. These directives are used during conditional compilation. In the .NET Framework exceptionhandling, an exception object that inherits from the ExceptionClass class is thrown from an area of codewhere an exception has occurred, the thrown exception is caught to avoid abnormal application program

termination. Unsafe code allows declaring and operating on pointers, to perform conversions betweenpointers and integral types, to take the address of variables, and so forth. Threading is supported by C#through the use of System.Threading. This class provides built-in features to support threading.

The .NET Framework library base classes are the foundation on which .NET applications, components,and controls are built. The .NET Framework base classes include classes, interfaces, and value types thatprovide access to system functionality. To facilitate interoperability between languages, the .NET Framework

base classes are CLS compliant and therefore can be used from any programming language. System.Objectclass is the ultimate base class that all types directly or indirectly derive from. In C#, a text string is storedin a data type named string, which is an alias to the System.String type. Array types are reference types

derived from the abstract base type System.Array. The System.Collections namespace contains interfacesand classes that define various collections of objects, such as lists, queues, bit arrays, hashtables anddictionaries.

QUESTIONS

1. What is a preprocessor? What does the #if, #else, #elif, #endif, #define, #undef, #warning, #error, and #line

directives do? Give examples for each.

2. What is an exception? How exceptions are handled in C#?

3. What is an unsafe code? Explain.

4. What is threading? List out the advantages and disadvantages of multiple threads.

5. Write a note in Library Base Classes.

6. What is the role of System.Object, System.String, System.Array and System.Collections Classes?

7. What are the different methods supported by System.Object class? Give an example for each.

8. What is boxing and unboxing? Explain with an example.

9. Write a program to replace all ‘r’ by ‘R’ in the string “rose is a rose”.

10. Write a note on

a. Single-Dimensional Arrays



b. Multidimensional Arrays

c. Jagged Arrays

d. Passing Arrays Using ref and out

11. What is the use of System.Collections class?

130

Chapter 7

Programming with ADO.NET


8 Have an ADO.NET working concept and its architecture

8 Learn how to use DataSet and DataProvider

8 See an ADO.NET implementation with example

7.1 ADO.NET OVERVIEW

ActiveX Data Objects for the .NET Framework (ADO.NET) is a set of classes that provide data

access services to the .NET programmer. ADO.NET provides a rich set of components for creating

distributed, data-sharing applications. It is an integral part of the .NET Framework, providing access to

relational database, XML, and application data. ADO.NET supports a variety of development needs,

including the creation of front end database clients and middle tier business objects used by applications,

tools, languages, or Internet browsers.

ADO.NET provides consistent access to data sources such as Microsoft SQL Server, or data sources

exposed via OLE DB and XML. Data sharing applications can use ADO.NET to connect to these data

sources and retrieve, manipulate, and update data.

ADO.NET includes .NET data providers or data adapters for connecting to a database, executing

commands, and retrieving results. Those results are either processed directly, or placed in an ADO.NET

Chapter 7 - Programming with Ado.NET

Chapter 7 - Programming with Ado.NET130


DataSet object in order for further processing. The ADO.NET DataSet object can also be used to

manage data local to the application.

ADO.NET is a kind of an abstraction layer, as shown in the figure 1.8. It lets us deal with some .NETclasses that simplify the whole issue of connecting to databases.

In this section, we will try to get a big picture about ADO.NET. If we get oriented correctly, we can

understand all the pieces and how they fit together.

Let us consider a problem to understand the underlying concept. We has a database somewhere andIt is connected to a SQL server. Now We need to build a form, and display some data from that databaseon the form. We will also use the User Interface widget called a datagrid to display data out of a relational

database. The problem considered until now can be represented in the below figure 7.1.

Figure 7.1 : Disconnected model with database server at one end and DataGrid control at the other end

We have a disconnected model. Now we will design our program using .NET ADO concept to implementthe above problem. We require a dataset. Dataset is a place where we are going to retrieve data from theserver and put it into the dataset. So now our above figure 7.1 will be something like below figure 7.2.

Figure 7.2 : Disconnected model with database server at one end. DataGrid control and DataSet at the other end

SQL

Server

SQL Database

Form

DataGrid

SQL

Server

SQL Database Form

DataGrid

DataSet

132

We will now going to use data binding to connect the datagrid automatically to the dataset, as shown infigure 7.3 below. When the dataset changes, the datagrid will show it. If the datagrid changes, it will bepushed down into the dataset.

SQL

Server

SQL Database Form

DataGrid

DataSet

Figure 7.3 : DataGrid control is bound to DataSet

We still have not bridge the gap from the SQL database to the dataset.

To do that we have the magic component class called a data adapter. A data adapter sits between thatdataset and the SQL server, as shown below. So now we have got a picture, but we still have to see, whatgoes on inside a data adapter and how we wire it up.

Figure 7.4 : Model is now connected by using Data Adapter

SQL Server

SQL Database

Form

DataGrid

DataSet

Data Adapter SQL Command – “Select * from Table1” SQL Connection – “data source = myComputer, …” Fill( myDataSet, myTable );



The data adapter needs a SQL commands. These SQL command select rows out of the table that weare interested in. In .NET we have an object of type SQL Command. It has a couple of properties thatwe need to set, and then we can use it, the data adapter can use it to interrogate the database. Knowinga SQL command isn’t enough, there might be a lot of databases with a lot of tables. We are selecting datafrom Table 1, but do not know where Table 1 is located in all these databases. For a SQL command toexecute, we have to use another .NET class called a SQL connection.

So, What is a SQL connection? Well, SQL connection has connection string and some other littleproperty, that has to be set. The connection string specifies things like, what machine is this database on,is there a password that is needed, what kind of security is involved with accessing this database? Allthese things can be set with the string inside the SQL connection.

Now, We have got our data grid connected to our dataset, we have instantiated a data adapter, wehave a SQL command to select data.

The data adapter has a method called Fill. What Fill does is, it use the Select command to go extractdata from the database. It creates a table inside the dataset. It puts those retrieved rows inside that tableof dataset, and it gives whatever name we want. So we have called it Table1. Once that data is in thedataset, it doesn’t matter where it came from, whether it was a SQL database, an XML database, etc.

So now the picture is clear, datagrid is bound to dataset with a data adapter sitting between it and thedatabase. We need a SQL command and a SQL connection, and then the program is ready to work.

7.2 ADO.NET ARCHITECTURE

Data processing has traditionally relied primarily on a connection based, two tier model. As dataprocessing increasingly uses multi-tier architectures, programmers are switching to a disconnected approachto provide better scalability for their applications.

XML and ADO.NET

ADO.NET leverages the power of XML to provide disconnected access to data. ADO.NET wasdesigned hand-in-hand with the XML classes in the .NET Framework. Both are components of a singlearchitecture.

ADO.NET and the XML classes in the .NET Framework converge in the DataSet object. The DataSetcan be populated with data from an XML source (file or an XML stream). The native serialization formatof the DataSet is XML, it is an excellent medium for moving data between tiers making the DataSet anoptimal choice for remoting data and schema context to and from an XML Web service.

134

ADO.NET Components

The ADO.NET components have been designed for easy data access and data manipulation. Thereare two central components of ADO.NET - the DataSet, and the .NET data provider. The .NET dataprovider is a set of components including the Connection, Command, DataReader, and DataAdapterobjects.

The ADO.NET DataSet is the core component of the disconnected architecture of ADO.NET. TheDataSet is explicitly designed for data access independent of any data source. It can be used with multipleand different data sources, used with XML data, or used to manage data local to the application. TheDataSet contains a collection of one or more DataTable objects are made up of rows and columns of data,as well as primary key, foreign key, constraint, and relation information about the data.

The other core element of the ADO.NET architecture is the .NET data provider, whose components(Connection, Command, DataReader, and DataAdapter) are explicitly designed for data manipulation andforward-only, read-only access to data. The Connection object provides connectivity to a data source.The Command object enables access to database commands to return data, modify data, run storedprocedures, etc. The DataReader provides a high-performance stream of data from the data source.Finally, the DataAdapter provides the bridge between the DataSet object and the data source. TheDataAdapter uses Command objects to execute SQL commands at the data source to both load theDataSet with data, and to update changes made to the data in the DataSet back to the data source.

The following diagram illustrates the components of ADO.NET architecture.

Figure 7.5 : Components of ADO.NET Architecture



Choosing a DataSet and a DataReader

When deciding whether our application should use a DataSet or DataReader, we should consider thetype of functionality that our application requires. We should use a DataSet to do the following:

l Remote data between tiers or from an XML Web service.

l Interact with data dynamically such as binding data to Forms control or combining and relatingdata from multiple sources.

l Cache data locally in our application.

l Provide a hierarchical XML view of relational data.

l Perform extensive processing on data without requiring an open connection to the data source.

If we do not require the functionality provided by the DataSet, we can improve the performance usingthe DataReader. Although the DataAdapter uses the DataReader to fill the contents of a DataSet, byusing the DataReader we can receive performance gains because we will save memory that will beconsumed by the DataSet, and also saving the processing required creating and filling the contents of theDataSet.

7.3 DATA PROVIDER

A .NET data provider is used for connecting to a database, executing commands, and retrievingresults. Those results are either processed directly, or placed in an ADO.NET DataSet. The .NET dataprovider is designed to be lightweight, creating a minimal layer between the data source and applicationcode, increasing performance without sacrificing functionality.

The following table outlines the four core components of .NET data provider.

Table 7.1 : Components of .NET Data Provider

Object Description

Connection Establishes a connection to a specified data source.

Command Executes a command against a data source.

DataReader Reads a forward-only, read-only stream of data from a data source.

DataAdapter Populates a DataSet and resolves updates with the data source.

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7.4 DATA SET

The DataSet object is central to supporting disconnected, distributed data scenarios with ADO.NET.The DataSet is a memory resident representation of data that provides a consistent relational programmingmodel regardless of the data source. The following illustration shows the DataSet object model.

DataSet object model

The methods and objects in a DataSet are consistent with those in the relational database model.

Figure 7.6 : Hierarchical diagram showing DataSet Class hierarchy

The DataTableCollection

An ADO.NET DataSet contains a collection of zero or more tables represented by DataTable objects.The DataTableCollection contains all the DataTable objects in a DataSet.

A DataTable is defined in the System.Data namespace and it represents a single table of data. Itcontains a collection of columns represented by a DataColumnCollection, and constraints represented bya ConstraintCollection, which together define the table schema. A DataTable also contains a collection ofrows represented by the DataRowCollection, a DataRow retains both its new and old changes to thevalues stored in the row.

DataSet

9 DataRelationCollection

9 ExtendedProperties

9 DataTableCollection

9 DataTable

9 DataRowCollection

9 DataRow

9 DataView

9 ChildRelations

9 ParentRelations

9 Constraints

9 DataColumnCollection

9 DataColumn

9 ExtentedProperties

9 ExtendedProperties

9 PrimaryKey



The DataRelationCollection

A DataSet contains all its relationships stored in its DataRelationCollection object. A relationship isrepresented by the DataRelation object, which associates rows in one DataTable with rows in anotherDataTable. It is something like a join path that might exist between primary and foreign key columns in arelational database. A DataRelation identifies matching columns in two tables of a DataSet.

Relationships enable navigation from one table to another within a DataSet. The essential elements ofa DataRelation are the name of the relationship, the name of the tables being related, and the relatedcolumns in each table. Relationships can be built with more than one column per table by specifying anarray of DataColumn objects as the key columns. When a relationship is added to theDataRelationCollection, it may optionally add a UniqueKeyConstraint and a ForeignKeyConstraint toenforce integrity constraints when changes are made to related column values.

ExtendedProperties

The DataSet has an ExtendedProperties property. ExtendedProperties is a PropertyCollection wherewe can place information, such as the SELECT statement that was used to generate the resultset, or adate/time stamp of when the data was generated

7.5 SAMPLE IMPLEMENTATION USING ADO.NET

This section demonstrates the basic database operations using the ADO.NET classes. The samplecode in this chapter uses the OleDb Provider.

Here is some sample code to execute a simple query.

Let us analyze the above code. First we have declared a connection string. The connection stringpoints to an MS Access database (Employee.mdb).

string connectionString = “Provider=Microsoft.Jet.OLEDB.4.0;DataSource=C:\\Samples\\Employee.mdb”;

OleDbConnection myConnection = new OleDbConnection( ConnectionString );myConnection.Open();

string query = “insert into EMPLOYEE_TABLE (EmployeeID, Name, Address)VALUES (101, ‘John’, ‘3960 CliffValley Way’)”;

OleDbCommand myCommand = new OleDbCommand();myCommand.CommandText = query;myCommand.Connection = myConnection;myCommand.ExecuteNonQuery();

myConnection.Close();

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In the next step, we are creating an OleDbConnection object and passing the connection string to thisobject. The line ‘myConnection.Open(); in the above code will open a connection to the MS Accessdatabase specified in the connection string. If the database does not exists or if it is not able to open aconnection for some other reason, the ‘.Open’ call will fail.

Next step is, creating an OleDbCommand object. This command object is used to execute SQLstatements and uses the connection opened by the OleDbConnection object. Note that before executinga command, we have to establish a valid connection to the database. And finally, after we have executedwith the command, we will close the connection.

The above code executes a SQL statement and returns no data from database. We are calling themethod ‘ExecuteNonQuery()’ on the command object. If we have a ‘select ...’ statement which returnsdata from database, we cannot use the ‘ExecuteNonQuery()’ method.

The following sample demonstrates using OleDbDataAdapter Object and DataSet to retrieve datafrom databbase.

Here in the above piece of code, we are creating an OleDbConnection object and we are just passingthe object to the OleDbDataAdapter object. Also, we pass the ‘select ...’ query to the OleDbDataAdapter.Next, we call the ‘.Fill()’ method of the OleDbDataAdapter. This step will populate the dataset ( called‘employeeData’ ) with the data retrieved for the SQL statement ‘select * from EMPLOYEE’

As you already know, a DataSet can contain a collection of tables. But in our case, our SQL statementwill retrieve data from only one table. So, our DataSet will have only one table

We can also iterate through the table in the dataset and retrieve all the records. See the following codedemonstrating it:

string connectionString = “Provider=Microsoft.Jet.OLEDB.4.0;DataSource=C:\\Samples\\Employee.mdb”;

OleDbConnection myConnection = new OleDbConnection(connectionString );

string query = “select * from EMPLOYEE_TABLE”;

OleDbDataAdapter myAdapter = new OleDbDataAdapter( query,myConnection );DataSet employeeData = new DataSet();myAdapter.Fill ( employeeData );

string connectionString = “Provider=Microsoft.Jet.OLEDB.4.0;DataSource=C:\\Samples\\Employee.mdb”;OleDbConnection myConnection = new OleDbConnection(connectionString );



The above code retrieves all the records from the employee table and displays all the fields.

SUMMARY

ADO.NET includes .NET data providers or data adapters for connecting to a database, executingcommands, and retrieving results. In ADO.NET data source is bound to dataset with a data adaptersitting between it and the database. ADO.NET leverages the power of XML to provide disconnectedaccess to data. ADO.NET was designed hand-in-hand with the XML classes in the .NET Framework. A.NET data provider is used for connecting to a database, executing commands, and retrieving results.Those results are either processed directly, or placed in an ADO.NET DataSet.

QUESTIONS

1. Give the overall concept of ADO.NET with the help of figures. (Hint: Big picture)

2. Explain in detail ADO.NET architecture.

3. What is a data provider? Explain.

4. What is a data set? Explain

5. Write a program to show the demonstration of ADO.NET.

string query = “select * from EMPLOYEE_TABLE”;

OleDbDataAdapter myAdapter = new OleDbDataAdapter( query,myConnection );DataSet employeeData = new DataSet();myAdapter.Fill( employeeData );

// Repeat for each table in the DataSet collection.foreach ( DataTable table in employeeData.Tables ){

// Repeat for each row in the table.foreach ( DataRow row in table.Rows ){

MessageBox.Show(“Employee Number : “ +row[“EmployeeNumber”].ToString());

MessageBox.Show( “Name : “ + row[“Name”].ToString() );MessageBox.Show( “Address : “ + row[“Address”].ToString() );

}}

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Chapter 8

Internet Programming

By the end of this chapter, you will have

8 An brief overview about internet programming in .NET framework

8 Learn how web services and web forms work

8 Learn briefly ASP.NET

In this chapter we will explore the .NET framework support for Internet-based programming. We aregoing to cover several topics under this Chapter. Firstly we will understand XML Web services, and nextwe will take Web Forms, which are browser-based Web applications. ASP.NET, is also a important topicto understand in internet programming.

8.1 WEB SERVICES

We will try to a big picture of what is this web service is? A Web service is a very simple idea. It isa application logic, accessible through some standard Web protocol.

At this point, a diagram will help us to get a big picture. The figure 8.1 below has a consumer of aservice on one side and a Web service on another side.

Chapter 8 - Internet Programming

Chapter 8 - Internet Programming140


Figure 8.1 : Request and Response process between application and web services

The consumer shots a request to the Web service. Web service or XML web service is just a collectionof methods that can be called from some other computer, from a remote location. The cloud in the middleof figure is the Internet. The result goes back to the consumer. To the consumer there is very littledifference from calling a method that is running on the same machine, but it is running at some otherlocation on the Internet.

Why do we call it XML Web services and why do we have that ‘XML’ label in the above figure? Well,XML is the tool that is used automatically to serialize the request and sent it using HTTP across theInternet to the Web service, if we are developing code in the .NET Framework. The Web service calculatesthe result, and that result is serialized into XML to get sent back to the consumer. At the consumer sidewe do the reverse of that process to regenerate whatever object was being returned by web service. Thatis the basic setup for Web services.

Now, the notion of a client on one side, issuing a request and getting a result back, is the same as WebPage using a browser. Then what is the difference between these two? Well, it is very similar, but notsame. Let us just compare the server browser model to the Web service model. It will be easy to see thedistinction.

Table 8.1 : Difference between Web page and Web services

XML

Consumer Application

Web Service

Request

Response

Web service is collection of

methods that can be called from

remote locations

Web Page Web Services

Has a User Interface No User Interface

Interacts with the user Interacts with application

Works with web browser client Works with any type of client

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For the above table, a Web page has a user interface. That is main part of it. A Web service does nothave user interface. A Web service is just between computer to computer applications. It is like a programon one computer calling a method that exists on another computer and calling it through the Internet. TheWeb page, since it has a user interface, it interacts with users. A Web service is designed to interact withapplications. It is code that is going to call my Web service, not some user by clicking some button. On theWeb-page side, naturally, a Web browser is the client. On the Web-service side, the client can be anythingthat can serialize a request and de-serialize the result that comes back. A fairly standard protocol calledSOAP does it all. So now we know the difference.

One thing that has to be mention here is. If we are building Web services using Visual Studio.NET andusing the full-fledged Microsoft Internet Information Service, IIS, Web server. We have to place all ourproject files in C drive’s directory called Inetpub, and inside that, a directory called WWWRoot. WWWRootdirectory is where all Web services are expected to be.

Web services is a big topic. We will quickly mention a couple of other things under this topic. Thoseare:

l Asynchronus Calls

l Exceptions

l Performance

l Security

l Evolution

A Web service can take a while to respond. When it is on the Internet, it has to do some computations.If the Web service calls some other service to get part of the answer or two or three other services to puttogether the response, that can take a few seconds. We normally do not want the client to freeze or blockwhile waiting for response. .NET provides an easy way for us to make an asynchronous call. We canmake the call to the Web service then carry on with whatever we want to do, while the Web service ischurning away. We can then later find out when it returns and collect the response.

Web service can throw an exception, and we handle it in our client code. We have already studied howthese exceptions are caught in ‘Advanced C#’ chapter, so we will not talk about it here.

Performance issue would make a difference if, we make lots of Web service calls. There is someoverhead to just making the call, so we would rather, keep our Web service interfaces chunky rather thanchatty. It is better to make a few calls that deliver to you a lot of information.

Security - The Web service can be completely insecure, when there is no authentication of user.Security plays a major role in internet domain. There are classes in .NET to address the security issue andauthenticate users



The last thing to mention here is that Web services, like Windows, are evolving a little bit. Newtechniques are adopted for the overall performance and efficiency of the web services.

8.2 WIN FORMS

With a Web Form, we have to use a browser. We can have browser to display a Web page that hassome controls on it, and can have interaction with that Web page and Web service. ASP.NET provides usWeb Forms for developing and running browser-based applications. It has a very rich set of GUI controlsthat we can use on our Web page. .Net provides all this in the form of WinForms. We can also put visualdesign on web page, we can specify a handler to be run back on the server, so the code behind thecontrols is done through server-side processing, and we can write that handler in any .NET language. Weare now able to program our Web page in C# also. Nice thing about this is it allows separation of thedesign; the HTML is used for any type of Web page, and for the server-side code any .NET languages.

To have a big picture for Win Forms, we will consider the following figure 8.2.

Figure 8.2 : Web Form event handling process

This time the client really is a Web page. It has a title, it has got some of Web-enabled user interfacedevices, Web controls (textboxes and buttons). These controls are used to fire event against the machinethat is serving the Web page. The user clicks a button, an event is fired, it goes through the Internet, it

Web Form

A B C

Web

Server

IIS

Event

Output Web page

Click

Server Scripts

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arrives over at the Web server like IIS. IIS has a couple of code files (server scripts) that have beencompiled. When the event fires, the event handler runs on the Web server. A Web page is dynamicallycreated with the result, and that is sent back to the user. This is the model for Web Forms, very similar toweb services but here It is just that the client is a browser.

There is a part of .NET called GDI+ which let us do fancy graphics, particularly in the area ofWinForms. There are parts of the library for string processing, with file I/O. String processing plays avery important role in the web designing area. There are cryptography classes in .NET. and .NET Remoting,which provides a more general approach to reaching out through the Internet than just Web services.

8.3 ASP.NET

Before going to ASP.NET let us see what is ASP. ASP is a Microsoft Technology and it stands forActive Server Pages. ASP is a server side scripting technology that enables scripts (embedded in HTMLpages) to be executed by an Internet server. ASP is a program that runs inside IIS (Internet InformationServices). An ASP file can contain text, HTML, XML, and scripts. Scripts in an ASP file are executed onthe server and an ASP file has the file extension “.asp”.

How Does it Work?

In case of a HTML file, when a browser requests an HTML file, the server returns the file. In case ofASP file, when a browser requests an ASP file, IIS passes the request to the ASP engine on the server.The ASP engine reads the file, line by line, and executes the scripts in the file. Finally, the ASP file isreturned to the browser as plain HTML. Before we study ASP .NET, it would help to have a basicunderstanding of the above ASP technology. So now with this little information about ASP we will moveto ASP.NET.

What is ASP.NET?

ASP.NET is the next generation ASP. ASP.NET is an entirely new paradigm for server-side ASPscripting. It is a part of the .NET Framework.

ASP.NET is a unified Web development platform that provides the services necessary for us to buildenterprise Web applications. While ASP.NET is largely syntax compatible with Active Server Pages(ASP), it provides a new programming model and infrastructure that allow us to create powerful applications.ASP.NET is part of the .NET Framework and allows us to take full advantage of the features of thecommon language runtime, such as type safety, inheritance, language interoperability, and versioning.

This section provides conceptual information about how ASP.NET works, and shows us how to writecode that takes full advantage of new platform.

ASP.NET is not just the next version of Active Server Pages (ASP); it is a unified Web development



platform that provides the services necessary for developers to build enterprise Web applications. ASP.NETprovides a new programming model and infrastructure for more secure, scalable, and stable applications.We can upgrade our existing ASP applications by incrementally adding ASP.NET functionality to them.

ASP.NET is a compiled, .NET-based environment; we can write applications in any .NET compatiblelanguage, including VisualBasic.NET, C#, and JScript .NET. Additionally, the entire .NET Framework isavailable to any ASP.NET application. Developers can easily use the benefits of these technologies,which include the managed CLR environment, type safety, inheritance, and so on.

ASP.NET has been designed to work seamlessly with WYSIWYG (What You See Is What You Get)HTML editors and other programming tools, including Microsoft Visual Studio .NET. Not only it makesWeb development easier, but it also provides all the benefits that tools offer, including a GUI that developerscan use to drop server controls onto a Web page and fully integrated debugging support.

Developers can choose the following two features when creating an ASP.NET application, WebForms and Web services, or combine these in any way they want it. Each is supported by the sameinfrastructure that allows us to use authentication schemes, cache frequently used data, or customize ourapplication’s configuration.

l Web Forms allows us to build powerful forms-based Web pages. When building these pages,we can use ASP.NET server controls to create common User Interface elements, and programthem for common tasks. These controls allow us to rapidly build a Web Form by reusablecomponents, simplifying the coding process.

l An XML Web service provides the means to access server functionality remotely. Using Webservices, distributed applications can manipulate data between client and server applications toimplement their business logic. XML Web services enable the exchange of data in client-serveror server-server scenarios, using standards like HTTP and XML messaging to move data acrossinternet. XML Web services are not bounded to a particular component technology or object-calling convention. As a result, programs written in any language, using any component model,and running on any operating system can access XML Web services.

Writing Your First ASP.NET Page

ASP.NET pages are text files with an .aspx file extension. These pages consist of code and markup.They are dynamically compiled and executed on the server to respond the requesting client browser.When a browser client requests .aspx resources, the ASP.NET runtime parses and compiles the targetfile into a .NET Framework class. This class can then be used to dynamically process incoming clientsrequests. The .aspx file is compiled only the first time it is accessed; the compiled type instance is thenreused across multiple requests.

An ASP.NET page can be created simply by taking an existing HTML file and changing its file nameextension to .aspx (no modification of code is required). For example, the following example demonstrates

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a simple HTML page that collects a user’s name and category preference and then performs a form postto the originating page when a button is clicked:

The output will be as shown in below figure

Figure 8.3 : Output screen shot of exam1.aspx program

Nothing happens when we click the Lookup button. This is because the exam1.aspx file contains onlystatic HTML (no dynamic content). Thus, the same HTML is sent back to the client when the button isclicked. In above output screen, if user enters the name as ‘Anne’, selects category as psychology and

// exam1.aspx<html> <head> <link rel=”stylesheet” href=”intro.css”> </head>

<body>

<center>

// Begin a form <form action=”exam1.aspx” method=”post”> <h3> Name: <input id=”Name” type=text> Category: <select id=”Category” size=1> <option>psychology</option> <option>business</option> <option>popular_comp</option> </select>

<input type=submit value=”Lookup”> </h3> </form> // End a form </center> </body></html>



click Lookup button. The same html form is again presented to user with form fields (the text box anddrop-down list) reset to their default values.

Adding Simple Code to a Page

ASP.NET provides syntax compatibility with existing ASP pages. This includes support for <% %>code blocks. The code listed between the <% and %> are executed to display data dynamically. This <%%> code blocks are intermixed with HTML content within an .aspx file. These code blocks execute in atop-down manner.

The below example demonstrates how <% %> blocks can be used to loop over an HTML block(increasing the font size each time):

The output will be as shown in the below figure

// exam2.aspx

<%@ Page Language=”C#”%>//This line specify that the C# language isused for coding

<html> <head> <link rel=”stylesheet”href=”intro.css”> </head>

<body> <center> <form action=”exam2.aspx” method=”post”> <h3> Name: <input id=”Name” type=text> Category: <select id=”Category” size=1> <option>psychology</option> <option>business</option> <option>popular_comp</option> </select> </h3> <input type=submit value=”Lookup”> <p>

<% for (int i=0; i <8; i++) { %> <font size=”<%=i%>”> Welcome to ASP.NET </font> <br> <% }%>

</form> </center> </body></html>

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When the button is clicked, the code between <% and %> is executed. As a result of it the “Welcometo ASP.NET” is printed 8 times in increasing order of their font size.

In case of ASP the code within <% %> are interpreted. But in ASP.NET <% %> blocks are actuallycompiled, not interpreted using a script engine. This results in improved runtime execution performance.

ASP.NET page developers can utilize <% %> code blocks to dynamically modify HTML output muchas they can today with ASP. For example, the following example demonstrates how <% %> code blockscan be used to interpret results posted back from a client.

The System.Web namespace supplies classes and interfaces that enable browser and servercommunication. This namespace includes the HttpRequest class which provides extensive informationabout the current HTTP request, the HttpResponse class which manages HTTP output to the client, andthe HttpServerUtility class which provides access to server-side utilities and processes. System.Web alsoincludes classes for cookie manipulation, file transfer, exception information, and output cache control.

In the below example we use the Request.QueryString, which gets the collection of HTTP querystring variables. These query string has form input values encoded within it. When the button is clickedthe exam3.aspx file is executed at server. The server extracts these query string values and sends it to theclient in HTML format. The client browser will print that message.



The output will be as shown in the below figure

// exam3.aspx

<%@ Page Language=”C#” %><html> <head> <link rel=”stylesheet”href=”intro.css”> </head>

<body> <center> <form action=”exam3.aspx”> <h3> Name: <input name=”Name” type=text value=“<%=HttpUtility.HtmlEncode(Request.QueryString[“Name”])%>”> Category: <select name=”Category” size=1>

<% String[] values = {“psychology”, business”,”popular_comp” }; for (int i=0; i<values.Length; i++) { %> <option <% if (Request.QueryString[“Category”] == values[i]) { Response.Write(“selected”); } %>> <%=values[i]%> </option> <% } %> </select>

</h3> <input type=submit name=”Lookup” value=”Lookup”> <p> <% if (Request.QueryString[“Lookup”] != null) { %> Hi<%=HttpUtility.HtmlEncode(Request.QueryString[“Name”]) %>, you selected:<%=HttpUtility.HtmlEncode(Request.QueryString[“Category”]) %> <% } %> </form> </center> </body>

</html>

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While <% %> code blocks provide a powerful way to manipulate the text box output returned from anASP.NET page.

Introduction to ASP.NET Server Controls

In addition to code and markup, ASP.NET pages can contain server controls, which are programmableserver-side objects that typically represent a user interface element in the page, such as a textbox orimage. Server controls simplify the problem of retaining state across round-trips to the server, automaticallyretaining their values across successive posts.

Server controls are declared within an .aspx file using custom tags or intrinsic HTML tags that containa runat=”server” attribute value. Intrinsic HTML tags are handled by one of the controls in theSystem.Web.UI.HtmlControls namespace. Any tag that does not explicitly map to one of the controls isassigned the type of System.Web.UI.HtmlControls.HtmlGenericControl.

The following example uses four server controls: <form runat=server>, <asp:textbox runat=server>,<asp:dropdownlist runat=server>, and <asp:button runat=server>. At run time these server controlsautomatically generate HTML content.

// exam4.aspx

<%@ Page Language=”C#”%><html> <head> <link rel=”stylesheet”href=”intro.css”> </head>

<body> <center> <form action=”exam4.aspx” method=”post” runat=server> <h3> Name: <asp:textbox id=”Name” runat=”server”/> Category: <asp:dropdownlist id=”Category” runat=server> <asp:listitem>psychology</asp:listitem> <asp:listitem>business</asp:listitem>



The output for the above program will be same as the output of very first example shown in figure 8.3.The only difference is, in that case the values entered where erased after clicking Lookup button but herein this program the values will be retained during the round trip to the server.

These server controls automatically maintain any client-entered values between round trips to theserver. This control state is not stored on the server (it is instead stored within an <input type=”hidden”>form field that is round-tripped between requests). Note also that no client-side script is required.

In addition to supporting standard HTML input controls, ASP.NET enables developers to utilize richercustom controls on their pages. For example, the following example demonstrates how the <asp:adrotator>control can be used to dynamically display rotating ads on a page.

<asp:listitem>popular_comp</asp:listitem> </asp:dropdownlist>

</h3> <asp:button text=”Lookup” runat=”server”/> </form> </center> </body></html>

// exam5.aspx

<%@ Page Language=”C#”%><html> <head> <link rel=”stylesheet”href=”intro.css”> </head>

<body> <center> <form action=”exam5.aspx” method=”post” runat=”server”> <asp:adrotator AdvertisementFile=”ads.xml”BorderColor=”black” BorderWidth=1 runat=”server”/> <h3> Name: <asp:textbox id=”Name” runat=”server”/> Category: <asp:dropdownlist id=”Category” runat=server> <asp:listitem>psychology</asp:listitem> <asp:listitem>business</asp:listitem> <asp:listitem>popular_comp</asp:listitem> </asp:dropdownlist> </h3> <asp:button text=”Lookup” runat=”server”/> </form> </center> </body></html>

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The output will be as show in the figure below


The above figure has rotating moments in the advertisement, which is not visible on this page.

//ads.xml file

<Advertisements>

<Ad> <ImageUrl>images/banner1.gif</ImageUrl> <NavigateUrl>http://www.microsoft.com</NavigateUrl> <AlternateText>Alt Text</AlternateText> <Keyword>Computers</Keyword> <Impressions>80</Impressions> </Ad>



</Advertisements>



Handling Server Control Events

Each ASP.NET server control is capable of exposing an object model containing properties, methods,and events. ASP.NET developers can use this object model to cleanly modify and interact with the page.

The following example demonstrates how an ASP.NET page developer can handle the OnClick eventfrom the <asp:button runat=server> control to manipulate the Text property of the <asp:label runat=server>control.

// exam6.aspx

<html> <head> <link rel=”stylesheet”href=”intro.css”> </head>

<script language=”C#” runat=server> void SubmitBtn_Click(Object sender, EventArgs e)

{ Message.Text = “Hi “ + HttpUtility.HtmlEncode(Name.Text) + “,you selected: “ + Category.SelectedItem; } </script>

<body> <center> <form action=”exam6.aspx” method=”post” runat=”server”> <asp:adrotator AdvertisementFile=”ads.xml”BorderColor=”black” BorderWidth=1 runat=”server”/> <h3> Name: <asp:textbox id=”Name” runat=”server”/> Category: <asp:dropdownlist id=”Category” runat=server> <asp:listitem>psychology</asp:listitem> <asp:listitem>business</asp:listitem> <asp:listitem>popular_comp</asp:listitem> </asp:dropdownlist> </h3> <asp:button text=”Lookup” OnClick=”SubmitBtn_Click”runat=”server”/> <p> <asp:label id=”Message” runat=”server”/> </form> </center> </body></html>

// ads.xml file<Advertisements> <Ad>

154

The output will be as shown below


This simple example given above is functionally equivalent to the “exam3” example. But code is muchcleaner and easier in this new server-control-based version.

Finally before ending this section, we will see another example which takes number of columns and

<ImageUrl>images/banner1.gif</ImageUrl> <NavigateUrl>http://www.microsoft.com</NavigateUrl> <AlternateText>Alt Text</AlternateText> <Keyword>Computers</Keyword> <Impressions>80</Impressions> </Ad>


<Ad> <ImageUrl>images/banner3.gif</ImageUrl> <NavigateUrl>http://www.microsoft.com</NavigateUrl> <AlternateText>Alt Text</AlternateText> <Keyword>Computers</Keyword> <Impressions>80</Impressions> </Ad></Advertisements>



number of rows from the user through the select list and displays a table corresponding to that many rowsand columns.

// exam7.aspx

<script runat=”server”>submit(Object sender, EventArgs e){

int row, numrows, numcells, j, i;row = 0;numrows = rows1.Value;numcells = cells1.Value;

for(j=1;j<=numrows;j++){

HtmlTableRow r = New HtmlTableRow();row += 1;

for(i=1; i<=numcells; i++){ HtmlTableCell c = New HtmlTableCell(); c.Controls.Add(New LiteralControl(“row “ & j & “, cell “& i)); r.Cells.Add(c);}t1.Rows.Add(r); t1.Visible=true;}

}</script>

<html><body>

<form runat=”server”><p>Table rows:<select id=”rows1" runat=”server”> <option value=”1">1</option> <option value=”2">2</option> <option value=”3">3</option></select><br />Table cells: <select id=”cells1" runat=”server”> <option value=”1">1</option> <option value=”2">2</option> <option value=”3">3</option></select><br /><br /><input type=”submit” value=”Display Table” runat=”server”OnServerClick=”submit”>

156

The output will be

SUMMARY

The .NET framework has extensible support for Internet-based programming. Web service is just acollection of methods that can be called from some other computer, from a remote location. Web Formuse a browser to display a Web page that has some controls on it, and can have interaction with that Webpage and Web service. ASP.NET is a unified Web development platform that provides the servicesnecessary for us to build enterprise Web applications. ASP.NET pages are text files with an .aspx fileextension. These pages consist of code and markup. They are dynamically compiled and executed on theserver to respond to the requesting client.

QUESTIONS

1. What is a web service? Explain its working.

2. Who does the web service differ from web page?

3. With a neat diagram explain the event handling process of win forms/web forms.

4. What is ASP.NET?

5. What is the use of ASP.NET?

6. Write a program to display “Welcome to ASP.NET” 8 times in increasing order of their font size using

ASP.NET.

7. What is the role of System.Web?

8. Write a program to demonstrate handling of server control events.

</p><table id=”t1" border=”1" runat=”server” visible=”false”/></form>

</body></html>



Chapter 9

.NET Remoting

By the end of this chapter, you will have

8 An brief overview about .NET Remoting

8 Knowledge about remoting process

8 Learn how to program .NET remoting

9.1 OVERVIEW

What is .NET Remoting?

.NET Remoting enables application communication. Different applications can communicate with oneanother, whether those applications reside on the same computer, on different computers in the same localarea network, or across the world in very different networks and even if the computers run differentoperating systems.

The .NET Framework provides a number of services such as activation and lifetime control. It alsoprovides communication channels responsible for transporting messages to and from remote applications.The messages can be encoded and decoded before they are sent along a channel. Applications can usebinary encoding when the performance is critical. It can also use XML encoding when interoperabilitywith other remoting systems is essential. Remoting was designed with security in mind, so we can serializestreams in order to secure them before they are transported over the channel.


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9.1.1 .NET Remoting, Distributed COM and Web Services

In this section we will compare all the three terminologies .NET Remoting, Distributed COM and Webservices which all seems same.

.NET Remoting versus Distributed COM (DCOM)

In the past interprocess communication between applications was handled through DistributedComponent Object Model, or simply DCOM. DCOM works well and the performance is adequate whenapplications exist on computers of similar type on the same network. However, DCOM has its drawbacks;it relies on a proprietary binary protocol that not all object models support. It also wants to communicateover a range of ports that are typically blocked by firewalls. These are two major drawbacks of DCOM.

.NET Remoting eliminates the difficulties of DCOM by supporting different transport protocol formatsand communication protocols. This allows .NET Remoting to be adaptable to the network environment inwhich it is being used.

.NET Remoting versus Web Services

When we read the description of .NET Remoting it reminds us a lot of what we have read about Webservices. That is because Web services fall under the roof of .NET Remoting, but web services have asimplified programming model and are intended for a wide target audience.

Web services involve allowing applications to exchange messages that may be platform independentand programming language independent. Web services know nothing about the client that is making therequest. The clients communicate by transferring messages back and forth in a specific format known asthe Simple Object Access Protocol, or SOAP

The following list gives some of the major differences between .NET Remoting and Web services:

l ASP.NET based Web services can only be accessed over HTTP. Whereas the .NET Remotingcan be used across any protocol.

l Web services work in a stateless environment where each request results in a new objectcreated to service the request. .NET Remoting supports state management options and canidentify multiple calls from the same client.

l Web services serialize objects through XML contained in the SOAP messages and can thusonly handle items that can be fully expressed in XML. .NET Remoting relies on the existence ofthe metadata within assemblies that contain information about data types. This limited metadatainformation is passed about an object, when it is passed by reference.

l Web services support interoperability across platforms and are good for heterogeneousenvironments. .NET Remoting requires the clients be built using .NET, which means ahomogeneous environment.

Chapter 9 - .NET Remoting


9.2 REMOTING PROCESS

Interprocess communication requires a server object whose functionality is to provide service to callersoutside its process. A client that makes calls on the server object, and a transportation mechanism will bethere from one end to the other. The addresses of server methods (services) are logical. These methodsfunction properly in one process, but needs some mechanism to work on different client processes locatedremotely. One way for the client to call a server object is by making a copy of the object entirety andmoves it to the client process, where the copy’s methods can be invoked directly.

Many objects should not be copied and moved to some other process for execution because of manyreasons. Firstly, extremely large objects with many methods can be poor choices for copying, to otherprocesses. Usually, a client needs only the information returned by one or a few methods on the serverobject. Copying the entire server object, including vast amounts of internal information or executablestructures unrelated to the client’s needs, would be a waste of bandwidth as well as of client memory andprocessing time. Copying these objects could be a problem from security point of view.

In these situations, the server process should pass to the client process a reference to the serverobject, not a copy of the object. Clients can use this reference to call the server object. These calls do notexecute in the client process. Instead, the remoting system collects all information about the call andsends it to the server process, where it is interpreted, the required server object is located, and the call ismade to the server object, by the server, on the client object’s behalf. The result of the call is then sentback to the client process by the server.

Remoting Architecture

Using object references to communicate between server objects and clients is the heart of remoting.The remoting architecture, however, presents to the programmer an even simpler procedure. If we configurethe client properly, we need only create a new instance of the remote object using new. Our clientreceives a reference to the server object, and we can then call its methods as though the object were inour process rather than running on a separate computer. The remoting system uses proxy objects tocreate the impression that the server object is in the client’s process. Proxies are stand-in objects thatpresent themselves as some other object. When our client creates an instance of the remote type, theremoting infrastructure creates a proxy object that looks to our client exactly like the remote type. Ourclient calls a method on that proxy, and the remoting system receives the call, routes it to the serverprocess, invokes the server object, and returns the return value to the client proxy, which returns the resultto the client.

Remote calls must be conveyed in some way between the client and the server process. If we werebuilding a remoting system ourselves, we might start by learning network programming and a wide arrayof protocols and serialization format specifications. But in the .NET Remoting system, the combination ofunderlying technologies required to open a network connection and use a particular protocol to send thebytes to the receiving application are represented as a transport channel.

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A channel is a type that takes a stream of data, creates a package according to a particular networkprotocol, and sends the package to another computer. Some channels can only receive information, otherscan only send information, and still others, such as the default TcpChannel and HttpChannel classes, canbe used in both directions.

The client knows only that it wants a reference an object in another application domain on anothercomputer. From the world outside the server application domain, the object is located by a URL. TheURLs that represent unique types to the outside world are activation URLs, which ensure that our remotecall is made to the proper type.

Complete Remoting System Design

Suppose we have an application running on one computer, and we want to use the functionality that isstored on another computer. The following figure shows the general remoting process.

SERVER CLIENT

Figure 9.1 : Remoting process

When both the server and client are configured properly, a client creates a new instance of the serverclass. The remoting system creates a proxy object that represents the class and returns to the client objecta reference to the proxy. When a client calls a method, the remoting system checks the type information,and sends the call over the channel to the server process. A listening channel picks up the request andforwards it to the server remoting system, which locates and calls the requested object. The process isthen reversed, as the server remoting system bundles the response into a message and the server channelsends to the client channel. Finally, the client remoting system returns the result of the call to the clientobject through the proxy.

Very little actual code is required to make this above concept work, but some thought should be givento the design and the configuration of the relationship. The code can be absolutely correct and but yet mayfail if a URL or port number is incorrect.



9.3 .NET REMOTING SAMPLE IMPLEMENTATION

In .NET Remoting, remote objects are accessed through Channels. Channels physically transport themessages to and from remote objects. There are two existing channels TcpChannel and HttpChannel,which use tcp and http protocols correspondingly

Create a Remotable Object

A remotable object is nothing more than an object that inherits from MarshalByRefObject. The followingsample demonstrates a simple class hello world. This object has a single method HelloWorld that willreturn a string. The only values that can be returned from methods are the classes in the .NET Frameworkthat are serializable such as string and DataSet. In addition, if we need to return a user-defined object thenthe object needs to be marked as serializable.

In below example we have a class called SampleObject, which is a remote object for this .NETremoting example. We have to add in our program a reference to System.Runtime.Remoting, otherwisethe TcpChannel will not be found. Compile the class and to get compiled code for this object.

Create a Server to Expose the Remotable Object

We need to create a server object that will act as a listener to accept remote object requests. For thisexample we will use the TCP/IP channel. We first create an instance of the channel and then we have toregister it for use by clients at a specific port. The service can be registered as

using System;using System.Runtime.Remoting;using System.Runtime.Remoting.Channels;using System.Runtime.Remoting.Channels.Tcp;

namespace Remoting{

// Sample remote object public class SampleObject : MarshalByRefObject {

// Constructor public SampleObject() { }

// Return a Hello world message public string HelloWorld() {

return “Hello World!”; }

}}

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WellKnownObjectMode.SingleCall, which results in a new instance of the object for each client, or asWellKnownObjectMode.Singleton, which results in one instance of the object used for all clients.

Since the service needs to be bound to an available port, In our example we use 8080, which is aunused port on the computer. We may need to choose a different port depending upon what ports that isavailable on the system (To see a list of the used ports on our computer open a command prompt and issuethe command “netstat —a”. It may produce a long listing so it is better making sure the command promptbuffer sizes are set to allow scrolling).

We have to add a class called SampleServer, as shown in the following code. Add a reference toSystem.Runtime.Remoting, otherwise the TcpChannel will not be found as mentioned earlier. In addition,we have to add a reference to the previous program containing the SampleObject, otherwise the code willnot compile because it won’t know how to find a reference to SampleObject.

Create a Client To Use the Remotable Object

Now that we have our remotable object and a server object to listen for requests, let us create a clientto use it. Our client will be very simple. It will connect to the server, create an instance of the object usingthe server, and then execute the HelloWorld method.


namespace Remoting{

// Sample serverpublic class SampleServer{

public static int Main(string [] args){

// Create an instance of a channelTcpChannel channel = new TcpChannel(8080);ChannelServices.RegisterChannel(channel);

// Register with the name HelloWorldRemotingConfiguration.RegisterWellKnownServiceType(

typeof(SampleObject), “HelloWorld”, WellKnownObjectMode.SingleCall );

System.Console.WriteLine(“Press the enter to exit...”);System.Console.ReadLine();return 0;

}}

}



Here we have a class called SampleClient in the following code. Again we have to add a reference toSystem.Runtime.Remoting. In addition, add a reference to the program containing the SampleObject.Compile the class.

Test the Remoting Sample

Once we have created all the above code and successfully compiled each of them, we are ready torun it. Assuming we chose a free TCP/IP port for the service, start the server executable. After theserver successfully starts it will display in a console window the message “Press the enter key to exit”.The server is listening so we are now ready to run the client. Executing the client should result in “HelloWorld!” being displayed in a separate console window. The client window will then close while the serverremains open and available.


namespace Remoting{

// Sample clientpublic class SampleClient{

public static int Main(string [] args){

// Create a channel for communicating with remote object// No port is specified on the clientTcpChannel chan = new TcpChannel();ChannelServices.RegisterChannel(chan);

// Create an instance of the remote objectSampleObject obj = (SampleObject) Activator.GetObject(

typeof(Remoting.SampleObject),”tcp://localhost:8080/HelloWorld” );

// Use the objectif( obj.Equals(null) ){ System.Console.WriteLine(“Error: Cannot locate server”);}else{ Console.WriteLine(obj.HelloWorld());}return 0;

}}

}

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We can try the example in a network, by executing the server on one machine and the client onanother. In order to run on separate machines we would need to change the reference to localhost in thesample client to point to the appropriate location.

SUMMARY

Different applications can communicate with one another, whether those applications reside on thesame computer, on different computers in the same local area network, or across the world in verydifferent networks and even if the computers run different operating systems using .NET Remoting. It ismore complicated to program against than the Web services. We need to decide for ourselves whetherour standard architecture is to use .NET Remoting or Web services. TcpChannel and HttpChannel classesare used to implement channel, this channel carries the messages between client and the server.

QUESTIONS

1. What is a .NET remoting?

2. How is .NET remoting different from web services and DCOM?

3. Explain remoting architecture.

4. With a neat diagram explain the remoting process.

5. Explain the steps or phases involved in implementing .NET remoting applications.

6. Write a program to display “Hello World” string to demonstrate .NET remoting.



REFERENCES

1. PROFESSIONAL C# by Simon Robinson, Ollie Cornes, Jay Glynn, Burton Harvey, Craig Cornes, Jerod Moemeka,

Christian Nagel, Morgan Skinner, Karli Watson, Wrox Press Ltd., July 2001

2. MSDN Library, www.microsoft.com/msdn

3. http://www.microsoft.com/seminar/mmcfeed/mmcdisplay.asp?Lang=en&Product=103364&Audience=100402

4. http://www.dotnetspider.com/technology

5. http://www.csharp-station.com

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