Delphi Command mode _delphi

This example is relatively well understood, so just give the code.
Unit pattern;
Interface
Uses Dialogs;
Type
Taudioplayer = class;
TCommand = Class
Public
Procedure Execute; Virtual Abstract
End
Tplaycommand = Class (TCommand)
Private
Audioplayer:taudioplayer;
Public
Procedure Execute; Override
Procedure Playcommand (Ap:taudioplayer);
End
Tstopcommand = Class (TCommand)
Private
Audioplayer:taudioplayer;
Public
Procedure Execute; Override
Procedure Stopcomman (Ap:taudioplayer);
End
Trewindcommand = Class (TCommand)
Private
Audioplayer:taudioplayer;
Public
Procedure Execute; Override
Procedure Rewindcommand (Ap:taudioplayer);
End
Tkeypad = Class
Private
Playcommand:tcommand;
Stopcommand:tcommand;
Rewindcommand:tcommand;
Public
Constructor Create (PLAYC, Stopc, Rewindc:tcommand); Virtual
Procedure play ();
Procedure Stop ();
Procedure Rewind ();
End
Taudioplayer = Class
Public
Procedure play ();
Procedure Stop ();
Procedure Rewind ();
End
TClient = Class
Private
Keypad:tkeypad;
Audioplayer:taudioplayer;
Public
Constructor Create ();
Procedure test ();
End
Implementation
{Tkeypad}
Constructor Tkeypad.create (PLAYC, Stopc, Rewindc:tcommand);
Begin
Playcommand: = PLAYC;
Stopcommand: = Stopc;
Rewindcommand: = REWINDC;
End
Procedure Tkeypad.play;
Begin
Playcommand.execute;
End
Procedure Tkeypad.rewind;
Begin
Rewindcommand.execute;
End
Procedure Tkeypad.stop;
Begin
Stopcommand.execute;
End
{Taudioplayer}
Procedure Taudioplayer.play;
Begin
ShowMessage (´play´);
End
Procedure Taudioplayer.rewind;
Begin
ShowMessage (´rewind´);
End
Procedure Taudioplayer.stop;
Begin
ShowMessage (´stop´);
End
{Tplaycommand}
Procedure Tplaycommand.execute;
Begin
inherited;
Audioplayer.play ();
End
Procedure Tplaycommand.playcommand (Ap:taudioplayer);
Begin
Self. Audioplayer: = AP;
End
{Trewindcommand}
Procedure Trewindcommand.execute;
Begin
inherited;
Audioplayer.rewind;
End
Procedure Trewindcommand.rewindcommand (Ap:taudioplayer);
Begin
Audioplayer: = AP;
End
{Tstopcommand}
Procedure Tstopcommand.execute;
Begin
inherited;
Audioplayer.stop;
End
Procedure Tstopcommand.stopcomman (Ap:taudioplayer);
Begin
Audioplayer: = AP;
End
{TClient}
Constructor Tclient.create;
Begin
Audioplayer: = Taudioplayer.create ();
End
Procedure Tclient.test;
Var
Playcommand:tcommand;
Stopcommand:tcommand;
Rewindcommand:tcommand;
Begin
Playcommand: = tplaycommand.create;
Stopcommand: = tstopcommand.create;
Rewindcommand: = trewindcommand.create;
Keypad: = Tkeypad.create (Playcommand, Stopcommand, Rewindcommand);
Keypad.stop;
Keypad.play;
Keypad.rewind;
Keypad.stop;
End
End.