• 定義：
  Facade（外觀）模式為子系統(tǒng)中的一組接口提供一個一致的界面，定義一個高層接口，這個接口使得這一子系統(tǒng)更加容易使用。

• UML:

  
  
  image.png
• 模型：
  家庭影院，包含DVD播放器，投影儀，自動屏幕，環(huán)繞立體聲，爆米花機等，這些社保都有開關設置功能。最后我們用遙控器控制各個社保的開關，實現(xiàn)播放家庭影院：

實現(xiàn)播放家庭影院步驟：
1開爆米花機
2.放下屏幕
3.開投影儀
4.開音響
5.開DVD，選dvd
6.去拿爆米花
7.調節(jié)燈光
總體來看我們想播放家庭影院需要很多的復雜的步驟，并且這些步驟都是固定的。而對于用戶并不關心這些步驟的操作過程，只要最后有爆米花，有的dvd看就行。外觀模式就是做這種事情的。我們通過外觀的包裝，使用戶只能看到外觀對象，而不會看到具體的細節(jié)對象，這樣無疑會降低應用程序的復雜度，并且提高了程序的可維護性。

image.png

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");
    }
}
//爆米花機
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");
    }   
}
//環(huán)繞立體聲
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);
        }
    }
}
//投影機
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);
    }
}
//屏幕
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");
    }   
}
//燈
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");
    }
     //調節(jié)亮度
    public void dim(int d) {
        System.out.println("TheaterLights dim to " + d + "%");
    }
    public void bright() {
        dim(100);
        System.out.println("TheaterLights bright");
    }
}
//包裝的外觀類
public class HomeTheaterFacade {
    private TheaterLights mTheaterLights;
    private Popcorn mPopcorn;
    private Stereo mStereo;
    private Projector mProjector;
    private Screen mScreen;
    private DVDPlayer mDVDPlayer;
        //注入各個設備對象
    public HomeTheaterFacade() {
        mTheaterLights = TheaterLights.getInstance();
        mPopcorn = Popcorn.getInstance();
        mStereo = Stereo.getInstance();
        mProjector = Projector.getInstance();
        mScreen = Screen.getInstance();
        mDVDPlayer = DVDPlayer.getInstance();
    }
        //固定的準備流程
    public void ready() {
        mPopcorn.on();
        mPopcorn.pop();
        mScreen.down();
        mProjector.on();
        mStereo.on();
        mDVDPlayer.on();
        mDVDPlayer.setdvd();
        mTheaterLights.dim(10);
    }
         //固定的關閉流程
    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();
    }
}

使用包裝的外觀對象操作家庭影院：

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

通過這樣的包裝，我們可以把外觀對象做成遙控器，這樣我們就能通過遙控器來實現(xiàn)家庭影院的控制。