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Prevent Derivation◄╣

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► KB ► To/From Guides ► C# ► Language Basics

Prevent Derivation (Cross Ref > Language Basics)

By Mike Prestwood

C# versus Delphi: A side by side comparison between C# and Delphi.

OOP Details

More object oriented (OO) stuff.

Prevent Derivation

[Other Languages]

Languages Focus

How do you prevent another class from inheriting and/or prevent a class from overriding a member.

C#: sealed

With C#, use the sealed keyword to prevent a class from being inherited from and to prevent a method from being overridden.

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

Syntax Example:

public class Machine : System.Object
{
  public virtual void Speak(String pSentence)
  {
    MessageBox.Show(pSentence);
  }
}
    
public class Robot : Machine
{
  public sealed override void Speak(String pSentence)
  {
    MessageBox.Show(pSentence);
  }
}

public sealed class Cyborg : Robot
{ 
}

Delphi: "Sealed class" sealed, final

With Delphi, use the sealed 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 = class sealed(TObject)
  public
    procedure Speak(pSentence: String); virtual; final;
  end;

Delphi Sealed class (sealed, final) 1 certification question.