Prestwood IT: Overriding (Cross Reference Coding Encyclopedia: C#)

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Overriding

General Info: Method Overriding

Where you define or implement a virtual method in a parent class and then replace it in a descendant class.

When you decide to declare a method as virtual, you are giving permission to derived classes to extend and override the method with their own implementation. You can have the extended method call the parent method's code too.

In most OO languages you can also choose to hide a parent method. When you introduce a new implementation of the same named method with the same signature without overriding, you are hiding the parent method.

C#: virtual, override

In C#, you specify a virtual method with the virtual keyword in a parent class and extend (or replace) it in a descendant class using the override keyword.

Use the base keyword in the descendant method to execute the code in the parent method, i.e. base.SomeMethod().

Syntax Example:

class Robot

  public virtual void Speak()

}
}

class Cyborg:Robot

  public override void Speak()

}
}

C# Overriding (virtual, override)

Cross Reference Examples:

ASP Classic: Not Supported

Since ASP Classic does not support inheritance, there is no concept of a descendant class nor overriding.

Corel Paradox: Not Supported

Delphi: virtual, override

In Delphi, you specify a virtual method with the virtual keyword in a parent class and extend (or replace) it in a descendant class using the override keyword. Call Inherited in the descendant method to execute the code in the parent method.

Syntax Example:

TRobot = class(TObject)
public
  procedure Speak; virtual;
end;

TCyborg = class(TRobot)
  procedure Speak; Override;
end;

Delphi Overriding (virtual, override)

Delphi Prism: virtual, override

Same as Delphi. In Prism, you specify a virtual method with the virtual keyword in a parent class and extend (or replace) it in a descendant class using the override keyword. Call Inherited in the descendant method to execute the code in the parent method.

Use final to prevent further extending of a member and Sealed to prevent all members of a class from further extension.

Syntax Example:

Robot = class(System.Object)
public
  method Speak; virtual;
end;

Cyborg = class(Robot)
public
  method Speak; override;
end;

Delphi Prism Overriding (virtual, override)

VB.Net: Overridable, Overrides

In VB.Net, you specify a virtual method with the Overridable keyword in a parent class and extend (or replace) it in a descendant class using the Overrides keyword.

Use the base keyword in the descendant method to execute the code in the parent method, i.e. base.SomeMethod().

Syntax Example:

Public Class Robot
  Public Overridable Sub Speak()
    MessageBox.Show("Robot says hi")
  End Sub
End Class

Public Class Cyborg
  Inherits Robot

  Public Overrides Sub Speak()
    MessageBox.Show("hi")
  End Sub
End Class

VB.Net Overriding (Overridable, Overrides)