设计模式——（9）外观模式_外观设计模式的类图-优快云博客

本文链接：https://blog.youkuaiyun.com/qq_36188127/article/details/125119803

第九章外观模式

1.1 引言

在现实世界中，观看电影可能需要如下步骤：

打开爆米花机
开始爆米花
将灯光调暗
放下屏幕
打开投影仪
将投影仪的输入切换到DVD
将投影仪设置在宽屏模式
…

可以看到观看电影需要对诸多子系统进行操作，因此，客户代码与诸多子系统耦合，为减少客户代码与子系统的耦合，引入外观模式。

1.2 外观模式

外观模式提供了一个统一的接口，用来访问子系统中的一群接口。外观定义了一个高层接口，让子系统更容易使用。

外观模式的类图如下图所示。

请添加图片描述

类图中的Facade是一个统一的接口，即高层接口，实现了客户与子系统之间的耦合。

1.3 使用外观模式——构造家庭电影院外观

定义电影院 HomeTheaterFacade 高层接口：

package headfirst.designpatterns.facade.hometheater;

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();
	}
}

客户代码 HomeTheaterTestDrive ：

package headfirst.designpatterns.facade.hometheater;

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();
	}
}

测试结果：

Cricket Game Initialized! Start playing.
Cricket Game Started. Enjoy the game!
Cricket Game Finished!

Football Game Initialized! Start playing.
Football Game Started. Enjoy the game!
Football Game Finished!

在外观模式中，使用了最少知识原则。