Override

This keyword from the C# programming language affects virtual method usage. Virtual methods are meant to be reimplemented in derived classes.

Replacement

The override keyword specifies that a method replaces its virtual base method. We use override in derived classes to replace inherited methods.

This program illustrates the difference between an override method in a derived class, and a method that is not an override method. It helps us learn about override methods.

using System;

class A
{
    public virtual void Y()
    {
        // Used when C is referenced through A.
        Console.WriteLine("A.Y");
    }
}

class B : A
{
    public override void Y()
    {
        // Used when B is referenced through A.
        Console.WriteLine("B.Y");
    }
}

class C : A
{
    public void Y() // Can be "new public void Y()"
    {
        // Not used when C is referenced through A.
        Console.WriteLine("C.Y");
    }
}

class Program
{
    static void Main()
    {
        // Reference B through A.
        A ab = new B();
        ab.Y();

        // Reference C through A.
        A ac = new C();
        ac.Y();
    }
}
B.Y
A.Y

Notes, example

The A type is used to reference the B and C types. When the A type references a B instance, the Y override from B is used.

A summary

The C# override modifier is needed for implementing polymorphic behaviors in derived classes. It is used in class inheritance.

Details, virtual

You can reimplement a virtual base method. This causes the base implementation to be ignored in favor of the "override" method.