C# Polymorphism

The term "Polymorphism" is the combination of "poly" + "morphs" which means many forms. It is a greek word. In object-oriented programming, we use 3 main concepts: inheritance, encapsulation and polymorphism.

There are two types of polymorphism in C#: compile time polymorphism and runtime polymorphism. Compile time polymorphism is achieved by method overloading and operator overloading in C#. It is also known as static binding or early binding. Runtime polymorphism in achieved by method overriding which is also known as dynamic binding or late binding.

C# Runtime Polymorphism Example

Let's see a simple example of runtime polymorphism in C#.

1. using System;  
2. public class Animal{  
3.     public virtual void eat(){  
4.         Console.WriteLine("eating...");  
5.     }  
6. }  
7. public class Dog: Animal  
8. {  
9.     public override void eat()  
10.     {  
11.         Console.WriteLine("eating bread...");  
12.     }  
13.       
14. }  
15. public class TestPolymorphism  
16. {  
17.     public static void Main()  
18.     {  
19.         Animal a= new Dog();  
20.         a.eat();  
21.     }  
22. }  

Output:

eating bread...

C# Runtime Polymorphism Example 2

Let's see a another example of runtime polymorphism in C# where we are having two derived classes.

1. using System;  
2. public class Shape{  
3.     public virtual void draw(){  
4.         Console.WriteLine("drawing...");  
5.     }  
6. }  
7. public class Rectangle: Shape  
8. {  
9.     public override void draw()  
10.     {  
11.         Console.WriteLine("drawing rectangle...");  
12.     }  
13.       
14. }  
15. public class Circle : Shape  
16. {  
17.     public override void draw()  
18.     {  
19.         Console.WriteLine("drawing circle...");  
20.     }  
21.   
22. }  
23. public class TestPolymorphism  
24. {  
25.     public static void Main()  
26.     {  
27.         Shape s;  
28.         s = new Shape();  
29.         s.draw();  
30.         s = new Rectangle();  
31.         s.draw();  
32.         s = new Circle();  
33.         s.draw();  
34.   
35.     }  
36. }  

Output:

drawing...
drawing rectangle...
drawing circle...

Runtime Polymorphism with Data Members

Runtime Polymorphism can't be achieved by data members in C#. Let's see an example where we are accessing the field by reference variable which refers to the instance of derived class.

1. using System;  
2. public class Animal{  
3.     public string color = "white";  
4.   
5. }  
6. public class Dog: Animal  
7. {  
8.     public string color = "black";  
9. }  
10. public class TestSealed  
11. {  
12.     public static void Main()  
13.     {  
14.         Animal d = new Dog();  
15.         Console.WriteLine(d.color);  
16.     
17.     }  
18. }  

Output:

white