Book notes

The Facade Pattern provides a unified interface to a set of interfaces in a subsystem. Facade defines a higher level interface that makes the subsystem easier to use.

Example

创建一个家庭影院的 facade class，封装家庭影院的多个子系统，提供统一的接口给客户端使用比如 watchMovie(), endMovie() 等，而不用逐一调用子系统的接口：

facade class:

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();
	}
}

component class:

skip

test code:

public class HomeTheaterTestDrive {
	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();
	}
}