Delphi 设计模式：《HeadFirst设计模式》Delphi7代码

1. 复杂的子系统
unit uSubObject;

interface

type

{ TAmplifier与TTuner，TCDPlayer，TDVDPlayer相互依赖。 }
{ 在TTuner等的简单实现时用不到对TAmplifier的引用， }
{ 但现实生活中就应该让TAmplifier提供服务，所以这里保留了。 }
{ TProjector对TDVDPlayer的引用也是同样道理。 }
{ 前置TAmplifier也可以，把TAmplifier的声明放在TTuner等声明的后面 }

TTuner = class;
TCDPlayer = class;
TDVDPlayer = class;

TAmplifier = class(TObject)
private
FTuner: TTuner;
FCD : TCDPlayer;
FDVD: TDVDPlayer;
FDescription: String;
public
constructor Create(aDescription: String);
procedure Open;
procedure Off;
procedure SetStereoSound;
procedure SetSurroundSound;
procedure SetVolume(aLevel: Integer);
procedure SetTuner (aTuner: TTuner);
procedure SetCD (aCD : TCDPlayer);
procedure SetDVD(aDVD: TDVDPlayer);
function ToString: String;
end;

TTuner = class(TObject)
private
FAmplifier: TAmplifier;
FDescription: String;
FFrequency: Double;
public
constructor Create(aDescription: String; aAmplifier: TAmplifier);
procedure Open;
procedure Off;
procedure SetAm;
procedure SetFm;
procedure SetFrequency(aFrequency: Double);
function ToString: String;
end;

TCDPlayer = class(TObject)
private
FAmplifier: TAmplifier;
FDescription: String;
FCurrentTrack: Integer;
FTitle: String;
public
constructor Create(aDescription: String; aAmplifier: TAmplifier);
procedure Open;
procedure Off;
procedure Eject;
procedure Play(aTitle: String ); overload;
procedure Play(aTrack: Integer); overload;
procedure Stop;
procedure Pause;
function ToString: String;
end;

TDVDPlayer = class(TObject)
private
FAmplifier: TAmplifier;
FDescription: