JAVA设计模式学习笔记-外观模式

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

一个设备

package com.java.test.facademode.hometheater;

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");
	}
}

另一种设备

package com.java.test.facademode.hometheater;

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");
	}
	
	
	
}

集中控制

package com.java.test.facademode.hometheater;

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();
	}
}

测试类

package com.java.test.facademode;

import com.java.test.facademode.hometheater.HomeTheaterFacade;



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

最少知识原则—最少知识原则的意义
最少知识原则：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