Wednesday, 10 April 2013

Abstract and Override Methods in C#

Abstract and Override Methods in C#

Abstract methods have no implementations. The implementation logic is provided rather by classes that derive from them. We use an abstract class to create a base template for derived classes.

Example

We introduce first an abstract class named Test. Two other classes derive from Test: the Example1 and Example2 classes. In the Test class, we have a field and also an abstract method.

Abstract methods cannot have bodies. This makes sense because those bodies would never be used.

using System;
abstract class Test
{
    public int _a;
    public abstract void A();
}
class Example1 : Test
{
    public override void A()
    {
       Console.WriteLine("Example1.A");
       base._a++;
    }
}
class Example2 : Test
{
    public override void A()
    {
       Console.WriteLine("Example2.A");
       base._a--;
    }
}
class Program
{
    static void Main()
    {
      // Reference Example1 through Test type.
      Test test1 = new Example1();
      test1.A();
      // Reference Example2 through Test type.
      Test test2 = new Example2();
       test2.A();
    }
}

Output
Example1.A
Example2.A

When you create a derived class like Example1 or Example2, you must provide an override method for all abstract methods in the abstract class. The A() method in both derived classes satisfies this requirement.

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