Overridding

rgowthamraj ramajayam

12y1.4kVisual Basic .NET

What is mean overridding?With Example

3 Replies

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rgowthamraj ramajayam12y ago
thank you so much
0
Joginder Banger12y ago
Virtual methods are meant to be re-implemented in derived classes.
The C# language provides the override modifier for this purpose.
This keyword specifies that a method replaces its virtual base method.

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();
}
}
Result B.Y A.Y
0
Vulpes12y ago
If you declare a method to be virtual in a base class, then it can be overridden in a derived class.

This means that the version of the method which gets called depends on the runtime type of the variable through which it's invoked and not its compile time type.

For example:

using System;

class Base
{
public virtual void ShowGreeting()
{
Console.WriteLine("Hello from Base class");
}
}

class Derived : Base
{
public override void ShowGreeting()
{
Console.WriteLine("Hello from Derived class");
}
}

class Program
{
static void Main()
{
Derived d = new Derived();
Base b = new Base();
Base bb = b;
bb.ShowGreeting(); // runtime type of bb is Base
bb = d;
bb.ShowGreeting(); // runtime type of bb is Derived
Console.ReadKey();
}
}

The output is:

Hello from Base class
Hello from Derived class

Overriding also applies to abstract methods of abstract base classes. The difference is that they must be overridden by concrete derived classes because the base class method cannot contain any implementation.

0