外观模式的定义
场景
观看家庭影院
场景描述
你组装了一套家庭影院，包含DVD播放器、投影机、自动屏幕、环绕立体声，甚至还有爆米花机，如下图：
现在你准备开始享受一部电影，你要做：
- 打开爆米花机；
- 开始爆米花；
- 将灯光调暗；
- 放下屏幕；
- … …（此处省略N步）
代码如下：
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| popper.on();
popper.pop();
lights.dim(10);
screen.down();
projector.on();
projector.setInput(dvd);
projector.wideScreenMode();
amp.on();
amp.setDvd(dvd);
amp.setSurroundSound();
amp.setVolume(5);
dvd.on();
dvd.play(movie);
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可以看到，播放电影我们就要做很多事情；同样，看完电影，你还要把一切都要关掉，还有很多事情等着你要去做。
方案
使用外观模式，通过实现一个提供了更合理接口的外观类，你可以将一个复杂的子系统变得容易使用。如果你需要原复杂子系统的强大威力，仍然可以使用原来的复杂接口；但如果你需要的是一个方便使用的接口，那么就使用外观类。
为家庭影院系统创建一个外观类HomeTheaterFacade，该类对外暴露出了几个简单的方法：watchMovie()、endMovie()、listenToRadio()、endRadio()。这个外观类将家庭影院的各个组件看作成一个子系统，通过这个子系统来实现外观类中的接口。这样，客户代码就可以调用此外观类所提供的方法，而不必再调用这个子系统中各个组件的方法。所以，想要看电影，只需要调用一个方法watchMovie()就行了。
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| public class HomeTheaterFacade {
Amplifier amp;
Tuner tuner;
StreamingPlayer player;
CdPlayer cd;
Projector projector;
TheaterLights lights;
Screen screen;
PopcornPopper popper;
public HomeTheaterFacade(Amplifier amp,
Tuner tuner,
StreamingPlayer player,
Projector projector,
Screen screen,
TheaterLights lights,
PopcornPopper popper) {
this.amp = amp;
this.tuner = tuner;
this.player = player;
this.projector = projector;
this.screen = screen;
this.lights = lights;
this.popper = popper;
}
public void watchMovie(String movie) {
System.out.println("Get ready to watch a movie...");
popper.on();
popper.pop();
lights.dim(10);
screen.down();
projector.on();
projector.wideScreenMode();
amp.on();
amp.setStreamingPlayer(player);
amp.setSurroundSound();
amp.setVolume(5);
player.on();
player.play(movie);
}
public void endMovie() {
System.out.println("Shutting movie theater down...");
popper.off();
lights.on();
screen.up();
projector.off();
amp.off();
player.stop();
player.off();
}
public void listenToRadio(double frequency) {
System.out.println("Tuning in the airwaves...");
tuner.on();
tuner.setFrequency(frequency);
amp.on();
amp.setVolume(5);
amp.setTuner(tuner);
}
public void endRadio() {
System.out.println("Shutting down the tuner...");
tuner.off();
amp.off();
}
}
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| public static void main(String[] args) {
Amplifier amp = new Amplifier("Amplifier");
Tuner tuner = new Tuner("AM/FM Tuner", amp);
StreamingPlayer player = new StreamingPlayer("Streaming Player", amp);
CdPlayer cd = new CdPlayer("CD Player", amp);
Projector projector = new Projector("Projector", player);
TheaterLights lights = new TheaterLights("Theater Ceiling Lights");
Screen screen = new Screen("Theater Screen");
PopcornPopper popper = new PopcornPopper("Popcorn Popper");
HomeTheaterFacade homeTheater =
new HomeTheaterFacade(amp, tuner, player,
projector, screen, lights, popper);
homeTheater.watchMovie("Raiders of the Lost Ark");
homeTheater.endMovie();
}
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外观模式VS适配器模式