In this example, the class DerivedClass is derived from an abstract class BaseClass. The abstract class contains an abstract method, AbstractMethod, and two abstract properties, X and Y.


// abstract_keyword.cs
// Abstract Classes
using System;
abstract class BaseClass   // Abstract class
{
    protected int _x = 100;
    protected int _y = 150;
    public abstract void AbstractMethod();   // Abstract method
    public abstract int X    { get; }
    public abstract int Y    { get; }
}

class DerivedClass : BaseClass
{
    public override void AbstractMethod()
    {
        _x++;
        _y++;
    }

    public override int X   // overriding property
    {
        get
        {
            return _x + 10;
        }
    }

    public override int Y   // overriding property
    {
        get
        {
            return _y + 10;
        }
    }

    static void Main()
    {
        DerivedClass o = new DerivedClass();
        o.AbstractMethod();
        Console.WriteLine("x = {0}, y = {1}", o.X, o.Y);
    }
}

output:
x = 111, y = 161


In the preceding example, if you attempt to instantiate the abstract class by using a statement like this:

BaseClass bc = new BaseClass();   // Error
 
you will get an error saying that the compiler cannot create an instance of the abstract class 'BaseClass'.