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.
Here In the example, the class A is the base class. It has the virtual method Y.
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.
But When the A type references a C instance, the Y method from the base class A is used.
Note The override modifier was not used. The C.Y method is local to the C type.
Warning The C type generates a warning because C.Y hides A.Y. Your program is confusing and could be fixed.
Tip If you want C.Y to really "hide" A.Y, you can use the new modifier, as in "new public void Y() in the declaration.
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.
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