Delphi Command模式

最近学习模式入迷， 所以就想写一篇关于模式的文章，这篇文章是<<Java 与模式>> （阎宏 著）里的一个例子， 我把它改成Delphi的.第一次写东西， 有不足之处希望大家可以谅解.
这个例子还是比较好理解的， 所以只给出代码.
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.