Lecture01

• 1. Object Oriented Software Modeling and DesignCE 350 Abdel-Karim Al-Tamimi, Ph.D. [email_address] http://faculty.yu.edu.jo/altamimi Al-Tamimi 2010

2. Overview

• Object Oriented Concepts

• Object Oriented Programming (OOP) vs. Structured/Procedural Programming

Al-Tamimi 2010 3. Introduction to OOP

• Things in real life areobjects , and an object has both:attributesandbehaviorsassociated with it

• Adamis a member of classPerson , as a member of this class it takes onPerson attributesandbehaviors

Walking, Eating, Sleeping, Eye-Color, Age, Height, Attributes Behaviors 4. OOP Concepts

• An object may have only attributes

• • Multiple attributes: struct

• • A single attribute(e.g. integer)

• Attributes = data

• Behavior = functions

• Restricting the access to objects data or functions is calleddata hiding

• Combining data and behavior in the same object is calledencapsulation

5. OOP vs. Procedural Programming Inputs Outputs object OOP Global Data Procedural Function 1 Function 2 Function 4 Function 3 6. Moving from Procedural to OOP

• Proceduralseparatesdata from the data-manipulations done on it

• OOPencapsulatesboth data and its manipulation inside one object

7. Procedural/Structured Programming

• Carry out the required tasks using functions, if the function is too big, break it down to smaller functions

• • Functional decomposition

• Functions are correlated with each other to form a data flow diagram (DFD)

Input Process Output 8. Structured Programming Students Exams Courses Tutors Add Student Enter for Exams Check Exam Marks Issue Certificate ExpelStudent 9. Structured Programming

• Harder to maintain as the system grows

• The impact of one change can affect many functions, which are hard to trace and to re-test

• To overcome these difficulties in maintaining the code and to perform expected adjustments, object oriented approach was introduced

10. How to Think in Terms of Objects

• Know the difference betweeninterfaceandimplementation

• Think more abstractly

• Give the user the minimal interface possible

11. Object to Object Communications MyObject AnotherObject Data Data MyFunction1 MyFunction2 Function_1 Function_2 12. Object to Object Communications

• Each object provide a specificinterfaceto allow other objects to communicate with it

• The classinterfaceincludes the following:

• • The method/function name

• • The inputs passed to the method/function

• • The return type of the method/function

• Any public data is considered also as a part of the class interface(better use get/set methods)

• By designing the class interfaces , the developerhideextra or sensitive data

13. Object to Object Communications 14. Interface vs. Implementation 15. Interface vs. Implementation

• Only the services the end user needs are represented

• • Data hiding with the use of encapsulation

• Change in the class implementation should not require change in the class users code

• • Interface is still the same

• Always provide the minimal interface

• Use abstract thinking in designing interfaces

• • No unnecessary steps

• • Implement the steps in the class implementation

16. Interface vs. Implementation Student Age, GPA, +getAge():integer +admit():void +expel():void +getFullName():string attributes methods 17. How to determine the minimum interface possible

• Only what the user absolutely needs

• • Fewer interfaces as possible

• • Use polymorphism

• Starts with hiding everything (private)

• • Only use public interfaces (try not to use public attributes, instead get/set)

• Design your class from the users perspective and what they need (meet the requirements)

18. Determining the Classs Environment

• Determine the class user

• • What type of technical programmer

• Determine the behavior of the object

• Environmental constraints on objects

• • Hardware or/and software constraints

• The next step is the implementation, anything that is not apublic interfaceis considered animplementation

19. Concept of Scope

• Local attributes

• • Local to a specific method

• Object attributes

• • Attributes shared between object methods

• Class attributes

• • Attributes share between objects

• • Starts withstaticidentifier

public class Employee{ static int Count; } 20. Object Attributes vs. Class Attributes 21. Inheritance

• Inheritanceallowsreusingcode, with a better organization and overall management

• Inheritanceallows classes to inherit attributes from other classes, and you can still overwrite common behaviors

• Inheritancecategorizes classes intosuperclasses(parent class) andsubclasses(child class)

22. Inheritance 23. Multiple Inheritance

• Class can inherit multiple classes

• In real life: kids inherit both father and mother attributes and behaviors

• Multiple inheritance is a complex solution that can solve complex problems elegantly

• • Problem to the designer

• • Problem to the programming language compiler writer

• • Java and C# decided not to allow it in the form C++ allows it

• C# uses interfaces to carry on the architecture of methods that a child class should have

24. Polymorphism

• Polymorphismmeans many shapes

• Polymorphismallows a single behavior to have different interfaces, and thus different inner-object behavior

• Polymorphismmeans thatsimilarobjects can respond to thesame messageindifferent manners

• Polymorphismgives the developer more options and different levels ofcustomizationto achieve a certain data manipulation or output

25. Polymorphism Al-Tamimi 2010 +ReturnArea():double Shape +ReturnArea():double Circle +ReturnArea():double Square Area= Length^2 Area= Radius^2Returns a double value 26. Polymorphism Al-Tamimi 2010 +GetArea(Shape) MainClass Will call Shape.ReturnArea() Area= Length^2 Area= Radius^2If shape is Circle If shape is Square 27. Constructors

• Only with objects

• No return value (even void)

• Method name is identical to class name

public Student(int StudentNumber) { /* Implementation Code */ }... Student BestStudent = new Student(1234); ... 28. Constructors

• Default constructor (no arguments)

• Any object will have a constructor even if you do not define it, since it inherits its superclass constructor

• • Every object is a subclass ofobjectclass

• • Superclass constructor is called by default

• Always provide a constructor

• Overloading methods/constructors

• • Same method name, different parameters

• • Polymorphism : using different objects that have the same superclass (child override parent)

29. Constructors

• Initialize all attributes

• Make sure that the initialization values leaves the object in a stable and safe state

• Do not include implementation in the constructor

• • Call a method if needed

Student Age, GPA, +Student: +getAge:integer +admit:void +expel:void +getFullName:string 30. Error Handling

• What can be done as a software developer when there is a potential risk of causing an error:

• • Ignore the problem that might cause the error

• • • Very dangerous, even if it has a very low probability

• • Check the problem then abort the program

• • • Handle the error by aborting the program, and show the error message

• • Check the problem, and try to fix it

• • • You already know how to fix it, may not be the best solution

• • Check the problem and throw an exception

• • • Throw the exception to the calling object to handle it

31. Exception Handling

• Exception is unexpected event that happens in the system

• We use keywords : tryandcatchandthrowto manage exceptions

try { // potential risky code } catch( Exception object) { // how to solve the exception // can not solve it, throw an exception } 32. Composition

• Compositionis to combine multiple objects to achieve a better or more complex objects

• Example: A computer is composed of different objects : memory, hard drive, motherboard, and each of these objects are composed of smaller objects etc

33. Resources

• Matt Weisfeld,The Object Oriented Thought Process , Sams Publishing, ISBN:0-672-32611-6