Override Details

• You cannot override a regular non-virtual method, nor a static method.
• The first version of the parent method must be virtual or abstract.
• You can override any parent method marked virtual, abstract, or override (already overridden).
• The methods must have the same signature.
• The methods must have the same visibility (the same access level).
• Use the base keyword to refer to the parent class as in base.SomeMethod().

C# Override Example

The following code snippet demonstrates using virtual and override to override a parent method in a descendant class.

using System;
 
class Dog

{

    public virtual void Bark()

    {

          Console.WriteLine("RUFF!");

    }
}
 

class GermanShepard:Dog

{

    public override void Bark()

    {

          Console.WriteLine("Rrrrooouuff!!");

    }
}
 

class Chiuaua:Dog

{

    public override void Bark()

    {

          Console.WriteLine("ruff");

    }
}
 

class InclusionExample

{

    public static void Main()

    {

         Dog MyDog=new Dog();
 

         MyDog=new GermanShepard();
         MyDog.Bark();  // prints Rrrrooouuff!!

         MyDog=new Chiuaua();

         MyDog.Bark();  // prints ruff;

    }
}

Hiding a Method with New

Use the new keyword to introduce a new implementation of a parent method (this hides the parent method). You can hide a method without using new but you will get a compiler warning. Using new will suppress the warning.

The new and override modifiers have different meanings. The new modifier creates a new member with the same name, signature, and visibility and hides the original member. The override modifier extends the implementation for an inherited member and allows you to implement inheritance-based polymorphism.

Avoid Introducing New Members: Sometimes there are clear reasons to introduce a new method with the same name, signature, and visibility of a parent method. In those clear cases, introducing a new member is a powerful feature. However, if you do not have a clear reason, then avoid introducing a new version of a method by naming the new method something unique and appropriate.

class Robot : System.Object
{
  public void Speak()
  {
    MessageBox.Show("Robot says hi");
  }
}

class Cyborg : Robot
{

  new public void Speak()
  {
    MessageBox.Show("hi");
  }
}

Calling the Base Class Version

A common task In OO is to extend a method by first executing the parent method code and then adding code. Use the base keyword to refer to the parent class as in base.SomeMethod().

class Robot : System.Object
{
  public virtual void Speak()
  {
    MessageBox.Show("Robot says hi");
  }
}

class Cyborg : Robot
{
  public override void Speak()
  {
  base.Speak(); 
  MessageBox.Show("hi");
  }
}