Prevent Derivation (VB.Net and Delphi Prism Cross Reference Guide)

With VB.Net, use the NotInheritable keyword to prevent a class from being inherited from and use the NotOverridable keyword to prevent a method from being overridden.

A method marked NotOverridable must override an ancestor method. If you mark a class NotInheritable, all members are implicitly not overridable so the NotOverridable keyword is not legal.

Public Class Machine

  Public Overridable Sub Speak(ByRef pSentence As String)
    MessageBox.Show(pSentence)
  End Sub
End Class

Public Class Robot
  Inherits Machine

  Public NotOverridable Overrides Sub Speak(ByRef pSentence As String)
    MessageBox.Show(pSentence)
  End Sub
End Class

Public NotInheritable Class Cyborg
  Inherits Robot
End Class

Same keywords as Delphi (sealed uses slightly different syntax). With Prism, use the sealed keyword before the class keyword to prevent a class from being inherited from and use the final keyword to prevent a method from being overridden.

Syntax Example:   type Robot = public sealed class(System.Object) public method Speak(pSentence: String); virtual; final; end;