Intro to object oriented programming

Principles of Object Oriented ProgrammingDavid GiardMCTS, MCSE, MCDBA, MCSD

DavidGiard.com

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Agenda

The ChallengeThe BasicsBringing Order To ChaosGuiding Principles

The Challenge

The Complexity of software derives from 4 elements:

Complexity of the problem domainDifficulty to manage the development processFlexibility possible through softwareSoftware problems often model discrete systems

How do you write great software every time??

Good question… lots of answers!

The customer–friendly programmer says:

“Great software always does what the customer wants it to. So even if the customer thinks of new ways to use the software, it doesn’t break or give them unexpected results.”

Good question… lots of answers!

The design–guru programmer says:

“Great software is when you use tried-and-true design patterns and principles. You’ve kept your objects loosely coupled, and your code opens for extension but closed for modification. That also helps keep the code more usable, so you don’t have to rework everything to use parts of your application over and over again.”

Good question… lots of answers!

The object-oriented programmer says:

“Great software is code that is object-oriented. So there's not a bunch of duplicate code, and each object pretty much controls its own behavior. It’s also easy to extend because your design is really solid and flexible.”

Make sure your software does what the customer wants

it to do.

Apply basic OO principles to add

flexibility

Strive for a maintainable,

reusable design

Answer: Simplify ComplexityAnswer: Eschew Obfuscation

The Basics

The BasicsObjectsClasses

MembersPropertiesMethodsEventsConstructors

InstancesMessage Passing

Defining Classesclass Name:BaseType{ // Members}

class MyType{ public String SomeString; public Int32 x; public Int32 y; public void DoSomething()

{…}

}

Class MembersFields

The state of an objectProperties

Also maintain stateMethods

ConstructorsFunctionsProperties (smart fields)

Members come in two basic formsInstanceStatic

FieldsMaintain state of an object

Accessing a field

class Point{ public Int32 X; public Int32 Y; private In32 _x;}

Point p = new Point();p.X = 100;p.Y = 200;Console.WriteLine(p.X);

PropertiesMethods that look like fields (smart fields)

Can have read-only or write-only properties

class Point{ Int32 _x; Int32 _y; public Int32 X { get{return _x;} set{_x = value;} } public Int32 Y { get{return _y;} set{_y = value;} }}

Methodsclass MyType{ public Int32 SomeMethod() { Int32 z = 0; // Code omitted… return z; }

public static void StaticMethod() { // Do something }}

MyType t = new MyType();t.SomeMethod();

Method Parametersclass MyType{ public Int32 AddNumbers(Int32 x, Int32 y) { Int32 z = x + y; return z; }

}

MyType t = new MyType();t.AddNumbers(1,2);

Types and Instances

Instantiating an Objectpublic class MyType{ public string MyStringField; public void InstanceMethod() { // Do something }}

MyType o = new MyType();o.MyStringField = “Hello”;String x = o.MyStringField;o.InstanceMethod();

Static Typespublic static class MyType{

public static void StaticMethod(){

// Do something}

}

MyType.StaticMethod();

ConstructorsConstructors are used to initialize fields

class Point{ private Int32 _x; private Int32 _y;

public Point() {

// Setup code }

public Point(Int32 xCoordinate, Int32 yCoordinate) { _x = xCoordinate; _y = yCoordinate; }}

Referencing an object

MyType obj1 = new MyType();obj2 = obj1;obj2.Color = “Red”;Console.WriteLine(obj1.Color)

Objects are reference typesPointer to memory

Event Handling

C# and VB have built in support for eventsGreat for dealing with objects in an event-driven operating systemMore than one type can register interest in a single eventA single type can register interest in any number of events

Event Handlingclass MyForm:Form{ MyForm(){ Button button = new Button(); button.Text = "Button"; button.Click += new EventHandler(HandleClick); Controls.Add(button); } void HandleClick(Object sender, EventArgs e){ MessageBox.Show("The Click event fired!"); } public static void Main(){ Application.Run(new MyForm()); } }

Designing Types: Accessibilities

public – Accessible to allprivate – Accessible to containing classprotected – Accessible to containing or derived classesinternal – Accessible to code in same assembly

Demo

Bringing Order to the ChaosObject Oriented Programming

Bringing Order to the Chaos Concepts of Object Orientation

EncapsulationAbstractionInheritancePolymorphismDecoupling

Bringing Order to the Chaos

EncapsulationandAbstraction

Bringing Order to the ChaosThe Role of Encapsulation

Car

EngineTransmission

Axel

Wheel

Wheel

Wheel

Wheel

Axel

Stop()

Drive()

Start()

Bringing Order to the ChaosThe Role of Abstraction

Layer 1

Module

Module

Layer 2

Module

Module

Layer 3Module Module

Demo

Bringing Order to the ChaosThe Role of Inheritance

Vehicle

Automobile

Car Truck

Plane

Jet Bi-Plane

InheritanceVehicle+Start()+Stop()+Steer()

Plane

Train

Automobile

+Start()+Stop()+Steer()+Fly()

+Start()+Stop()+Steer()+BlowHorn()

+Start()+Stop()+Steer()+Honk()

PolymorphismSportPlayerPlay()

BaseballPlayerPlay()Catch()

Catcherplay()Catch()

Outfielderplay()Catch()

FootballPlayerPlay()

ReceiverPlay()

Designing Types: PolymorphismUse the virtual keyword to make a method virtualIn derived class, override method is marked with the override keywordExample

ToString() method in Object class

Example derived class overriding ToString()

public virtual string ToString();

class SomeClass:Object{ public override String ToString(){ return “Some String Representing State”; }}

Demo

InterfacesDefine public membersNo ImplementationYour types can implement interfacesMust implement all methods in the interface

interface IName{ // Members}

Class ClassName : IName{}

Bringing Order to the ChaosThe Role of Decoupling

Demo

UML and Class Diagrams

Airplane

speed: int

getSpeed(): int

setSpeed(int)

Class Diagram

Member Variables

name:type

Name

Methods

name(parameters the method uses): return type

Visual Studio Class Designer

Demo

Guiding Principles

SOLID Principles

Single responsibilityOpen CloseLiskov Substitution.Interface Segregation Dependency Injection

Liskov substitution

public class Rectangle{ public virtual int Height { get; set; } public virtual int Width { get; set; }

public int Area() { return Height * Width; }}

Liskov substitution

rectangle.Height = 4;rectangle.Width = 5;int expectedArea = 20;int actualArea = rectangle.Area();Debug.Assert(expectedArea == actualArea);

Liskov substitutionpublic class Square : Rectangle { public override int Height { get { return base.Height; } set { base.Height = value; base.Width = value; } } public override int Width { get { return base.Width; } set { base.Width = value; base.Height = value; } }}

Liskov substitution

Rectangle square = new Square();square.Width = 4;square.Height = 5;int expectedArea = 20;int actualArea = rectangle.Area();Debug.Assert(expectedArea == actualArea);

Interface segregation principle

interface IWorker {public void work();public void eat();

}

Interface segregation principle

public class Customer { private IFoo _foo; public Customer(IFoo foo) { this._foo = foo; }}

David GiardDavidGiard.comTechnologyAndFriends.comDavidGiard@DavidGiard.comTwitter.com/DavidGiard

Special thanks to Chris Woodruff