设计模式--外观模式

 

外观模式原理
·一个家庭影院项目
组建一个家庭影院：
DVD播放器、投影仪、自动屏幕、环绕立体声、爆米花机

·传统的控制接口设计
直接用遥控器：统筹各设备开关
开爆米花机
放下屏幕
开投影仪
开音响
开DVD，选dvd
去拿爆米花
调暗灯光
播放
观影结束后，关闭各种设备

·外观模式的原理和设计

外观模式：提供一个统一的接口，来访问子系统中一群功能相关接口
外观模式定义了一个高层接口，让子系统更容易使用

代码演示
Popcorn 

public class Popcorn {


	private static Popcorn instance = null;

	private Popcorn() {

	}

	public static Popcorn getInstance() {
		if (instance == null) {
			instance = new Popcorn();
		}

		return instance;
	}
	
	public void on() {
		System.out.println("Popcorn On");
	}

	public void off() {
		System.out.println("Popcorn Off");
	}

	public void pop() {
		System.out.println("Popcorn is popping");
	}
	
	
	
}

Projector

public class Projector {
	private int size=5;

	private static Projector instance = null;

	private Projector() {

	}

	public static Projector getInstance() {
		if (instance == null) {
			instance = new Projector();
		}

		return instance;
	}
	
	public void on() {
		System.out.println("Projector On");
	}

	public void off() {
		System.out.println("Projector Off");
	}

	public void focus() {
		System.out.println("Popcorn is focus");
	}
	
	public void zoom(int size) {
		this.size=size;
		System.out.println("Popcorn zoom to"+size);
	}
	
}

DVDPlayer

public class DVDPlayer {



	private static DVDPlayer instance = null;

	private DVDPlayer() {

	}

	public static DVDPlayer getInstance() {
		if (instance == null) {
			instance = new DVDPlayer();
		}

		return instance;
	}
	
	public void on() {
		System.out.println("DVDPlayer On");
	}

	public void off() {
		System.out.println("DVDPlayer Off");
	}

	public void play() {
		System.out.println("DVDPlayer is playing");
	}
	
	public void pause() {
		System.out.println("DVDPlayer  pause");
	}
	
	public void setdvd() {
		System.out.println("DVDPlayer  is setting dvd");
	}
}

Screen

public class Screen {



	private static Screen instance = null;

	private Screen() {

	}

	public static Screen getInstance() {
		if (instance == null) {
			instance = new Screen();
		}

		return instance;
	}
	
	public void up() {
		System.out.println("Screen  up");
	}

	public void down() {
		System.out.println("Screen  down");
	}

	
	
	
	

}

Stereo

public class Stereo {

	private static Stereo instance = null;
	private int volume = 5;

	private Stereo() {

	}

	public static Stereo getInstance() {
		if (instance == null) {
			instance = new Stereo();
		}

		return instance;
	}

	public void on() {
		System.out.println("Stereo On");
	}

	public void off() {
		System.out.println("Stereo Off");
	}

	public void setVolume(int vol) {

		volume = vol;
		System.out.println("the volume of Stereo is set to  " + volume);
	}

	public void addVolume() {
		if (volume < 11) {
			volume++;
			setVolume(volume);
		}

	}

	public void subVolume() {
		if (volume > 0) {
			volume--;
			setVolume(volume);
		}

	}

}

TheaterLights 

public class TheaterLights {

	private static TheaterLights instance = null;

	private TheaterLights() {

	}

	public static TheaterLights getInstance() {
		if (instance == null) {
			instance = new TheaterLights();
		}

		return instance;
	}

	public void on() {
		System.out.println("TheaterLights On");
	}

	public void off() {
		System.out.println("TheaterLights Off");
	}

	public void dim(int d) {
		System.out.println("TheaterLights dim to " + d + "%");
	}

	public void bright() {
		dim(100);
		System.out.println("TheaterLights bright");
	}
}

控制类HomeTheaterFacade 

public class HomeTheaterFacade {
	private TheaterLights mTheaterLights;
	private Popcorn mPopcorn;
	private Stereo mStereo;
	private Projector mProjector;
	private Screen mScreen;
	private DVDPlayer mDVDPlayer;

	public HomeTheaterFacade() {
		mTheaterLights = TheaterLights.getInstance();
		mPopcorn = Popcorn.getInstance();
		mStereo = Stereo.getInstance();
		mProjector = Projector.getInstance();
		mScreen = Screen.getInstance();
		mDVDPlayer = DVDPlayer.getInstance();
	}

	public void ready() {
		mPopcorn.on();
		mPopcorn.pop();
		mScreen.down();
		mProjector.on();
		mStereo.on();
		mDVDPlayer.on();
		mDVDPlayer.setdvd();
		mTheaterLights.dim(10);
	}

	public void end() {
		mPopcorn.off();
		mTheaterLights.bright();
		mScreen.up();
		mProjector.off();
		mStereo.off();
		
		mDVDPlayer.setdvd();
		mDVDPlayer.off();
		
	}

	public void play() {
		mDVDPlayer.play();
	}

	public void pause() {
		mDVDPlayer.pause();
	}
}

MainTest 

public class MainTest {
	public static void main(String[] args) {
		HomeTheaterFacade mHomeTheaterFacade=new HomeTheaterFacade();
		
		mHomeTheaterFacade.ready();
		mHomeTheaterFacade.play();
	}
}

·外观模式与命令模式

外观模式和命令模式各自侧重点
外观模式的侧重点：在一个系统里建立接口，实现什么功能暴露出来，外面调用时不需要知道里面的细节，对外暴露的接口只有一个，外面和里面可以得到解耦；
命令模式的侧重点：把命令包装成对象，实现控制器与命令的解耦。


 最少知识原则
·最少知识原则的意义:尽量减少对象之间的交互，只留几个“密友”,项目设计中就是不要让太多的类耦合在一起

·如何遵循最少知识原则
对象的方法调用范围：
该对象本身
作为参数传进来的对象
此方法创建和实例化的对象
对象的组件

看个Car类的例子
 

public class Car{
	Engine engine;
	public Car()
	{
		//初始化发动机
	}
	
	public void start(Key mKey)
	{
		Doors doors=new Doors();
		boolean authorized=mKey.turns();   //违背了原则
		if(authorized)
		{
			engine.start();
			doors.lock();
		}
	}

}

·外观模式和最少知识原则