IEG3080 Tutorial 4

1. IEG3080 Tutorial 4 Prepared by KK

2. Outline • Object Oriented Programming Concepts • Encapsulation • Inheritance • Polymorphism • Delegation • Course Project

3. Polymorphism • What is it? • one name, many forms • future extension in the form of new types of objects is easy, if the new objects conform to the original interface. • How to do? • Method overloading • Method overriding through inheritance • Method overriding through the C# interface

4. Polymorphism • Method overloading • compile-time polymorphism • have the same name, but have different formal argument lists • within a class definition • within the class inheritance hierarchy

5. Polymorphism class Shape : Object { public void Draw() { Console.WriteLine("Draw apolygon"); } public void Draw(string s) { Console.WriteLine("Draw a {0}",s); } };

6. Polymorphism Shapes1 = new Shape(); s1.Draw(); s1.Draw(“square"); //Output Draw apolygon Draw asquare

7. Polymorphism class NewShape : Shape { public void Draw(inti) { Console.WriteLine("Draw many polygon"); } };

8. Polymorphism Shapes1 = new NewShape(); s1.Draw(); s1.Draw(“square"); s1.Draw(1); //Output Draw apolygon Draw asquare Draw many polygon

9. Polymorphism • Method overriding • runtime polymorphism • The decision cannot be made at compile time • The version of the method that was executed was based on the actual type of the object, and not on the type of the reference.

10. Polymorphism class A{   public virtual void m(){     System.Console.WriteLine("m in class A");   } } class B : A{   public override void m(){     System.Console.WriteLine("m in class B");   } } public class Test{   public static void TestMain(){     Object var = new B(); ((B)var).m();    //m in class B ((A)var).m();    //m in class B    //var.m();   //will not compile       } }

11. Reference • http://www.dickbaldwin.com/tocCsharp.htm • http://en.wikipedia.org/wiki/Polymorphism_in_object-oriented_programming • http://msdn2.microsoft.com/en-us/vcsharp/aa336809.aspx • http://msdn2.microsoft.com/en-us/library/ms173152(VS.80).aspx

12. Delegation • What is it? • take place at run-time • pass control to some other object through a delegation link, not an object reference • similar to a function pointer in C or C++ • encapsulate a reference to a method inside a delegate object

13. Delegation •     public class A    {        public void Process()        {            Console.WriteLine("Process() begin");            Console.WriteLine("Process() end");        }    }    public class B    {        static void Process()        {            A a1 = new A();            a1.Process(); //no delegation        }    }

14. Delegation • A delegate will allow us to specify what the function we'll be calling looks like without having to specify which function to call • delegate result-type identifier ([parameters]);

15. Delegation • namespace Tutorial.BasicDelegate{    // Declarationpublic delegate void SimpleDelegate();    class A    {        public static void foo()        {            Console.WriteLine(“Delegate...");        }        public static void Main()        {            // InstantiationSimpleDelegate simpleDelegate = new SimpleDelegate(foo);            // InvocationsimpleDelegate();        }    }}

16. Delegation     // Delegate Specification    public class A    {        // Declarationpublic delegate void ADelegate(string s);        // Checking         public void Process(ADelegate aDelegate)        {            if (aDelegate != null){                aDelegate(“Delegate…");            }        }    }public class B     {        // Constructor        public B(string s){}        // Member Function which is used in the Delegate        public void Func(string s)        {            Console.WriteLine(“{0}“,s);        }    }

17. Delegation     public class TestApplication    {        static void Main(string[] args)        {            B b1 = new B(“test");            A a1 = new A();            // Crate an instance of the delegate, pointing to the Logger()            // function on the fl instance of a FileLogger.            A.ADelegate aDelegate = new A.ADelegate(b1.Func);            A.Process(aDelegate);        }    }

18. Delegation • classes are indepentdently of one another, which makes for code that is easier to maintain • any number of classes can be notified when an event is raised

19. Reference • http://www.akadia.com/services/dotnet_delegates_and_events.html • http://en.wikipedia.org/wiki/Delegation_(programming)

20. Office : Room 803 • Office Hour : Tuesdays 16:30 – 17:15