設計模式——外觀模式（Facade Pattern）

外觀模式提供了一個統一的接口，用來訪問子系統中的一羣接口。外觀定義了一個高層接口，讓子系統更容易使用。

類圖

（圖片源於網絡）

代碼實現（Java）

// HomeTheaterFacade.java
public class HomeTheaterFacade {
    Amplifier amp;
    Tuner tuner;
    DvdPlayer dvd;
    CdPlayer cd;
    Projector projector;
    TheaterLights lights;
    Screen screen;
    PopcornPopper popper;
                                       
    public HomeTheaterFacade(Amplifier amp,
                 Tuner tuner,
                 DvdPlayer dvd,
                 CdPlayer cd,
                 Projector projector,
                 Screen screen,
                 TheaterLights lights,
                 PopcornPopper popper) {
                                       
        this.amp = amp;
        this.tuner = tuner;
        this.dvd = dvd;
        this.cd = cd;
        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.setDvd(dvd);
        amp.setSurroundSound();
        amp.setVolume(5);
        dvd.on();
        dvd.play(movie);
    }
                                       
                                       
    public void endMovie() {
        System.out.println("Shutting movie theater down...");
        popper.off();
        lights.on();
        screen.up();
        projector.off();
        amp.off();
        dvd.stop();
        dvd.eject();
        dvd.off();
    }
    public void listenToCd(String cdTitle) {
        System.out.println("Get ready for an audiopile experence...");
        lights.on();
        amp.on();
        amp.setVolume(5);
        amp.setCd(cd);
        amp.setStereoSound();
        cd.on();
        cd.play(cdTitle);
    }
    public void endCd() {
        System.out.println("Shutting down CD...");
        amp.off();
        amp.setCd(cd);
        cd.eject();
        cd.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();
    }
}

// Tuner.java
public class Tuner {
    String description;
    Amplifier amplifier;
    double frequency;
                                       
    public Tuner(String description, Amplifier amplifier) {
        this.description = description;
    }
                                    
    public void on() {
        System.out.println(description + " on");
    }
                                    
    public void off() {
        System.out.println(description + " off");
    }
                                    
    public void setFrequency(double frequency) {
        System.out.println(description + " setting frequency to " + frequency);
        this.frequency = frequency;
    }
                                    
    public void setAm() {
        System.out.println(description + " setting AM mode");
    }
                                    
    public void setFm() {
        System.out.println(description + " setting FM mode");
    }
                                     
        public String toString() {
                return description;
        }
}

// Screen.java
public class Screen {
    String description;
                                   
    public Screen(String description) {
        this.description = description;
    }
                                
    public void up() {
        System.out.println(description + " going up");
    }
                                
    public void down() {
        System.out.println(description + " going down");
    }
                                
                                 
        public String toString() {
                return description;
        }
}

// PopcornPopper.java
public class PopcornPopper {
    String description;
                                
    public PopcornPopper(String description) {
        this.description = description;
    }
                             
    public void on() {
        System.out.println(description + " on");
    }
                             
    public void off() {
        System.out.println(description + " off");
    }
    public void pop() {
        System.out.println(description + " popping popcorn!");
    }
                             
                              
        public String toString() {
                return description;
        }
}

// Amplifier.java
public class Amplifier {
    String description;
    Tuner tuner;
    DvdPlayer dvd;
    CdPlayer cd;
                            
    public Amplifier(String description) {
        this.description = description;
    }
                         
    public void on() {
        System.out.println(description + " on");
    }
                         
    public void off() {
        System.out.println(description + " off");
    }
                         
    public void setStereoSound() {
        System.out.println(description + " stereo mode on");
    }
                         
    public void setSurroundSound() {
        System.out.println(description + " surround sound on (5 speakers, 1 subwoofer)");
    }
                         
    public void setVolume(int level) {
        System.out.println(description + " setting volume to " + level);
    }
    public void setTuner(Tuner tuner) {
        System.out.println(description + " setting tuner to " + dvd);
        this.tuner = tuner;
    }
                          
    public void setDvd(DvdPlayer dvd) {
        System.out.println(description + " setting DVD player to " + dvd);
        this.dvd = dvd;
    }
                         
    public void setCd(CdPlayer cd) {
        System.out.println(description + " setting CD player to " + cd);
        this.cd = cd;
    }
                         
    public String toString() {
        return description;
    }
}

// CdPlayer.java
public class CdPlayer {
    String description;
    int currentTrack;
    Amplifier amplifier;
    String title;
                         
    public CdPlayer(String description, Amplifier amplifier) {
        this.description = description;
        this.amplifier = amplifier;
    }
                      
    public void on() {
        System.out.println(description + " on");
    }
                      
    public void off() {
        System.out.println(description + " off");
    }
    public void eject() {
        title = null;
        System.out.println(description + " eject");
    }
                      
    public void play(String title) {
        this.title = title;
        currentTrack = 0;
        System.out.println(description + " playing \"" + title + "\"");
    }
    public void play(int track) {
        if (title == null) {
            System.out.println(description + " can't play track " + currentTrack +
                    ", no cd inserted");
        } else {
            currentTrack = track;
            System.out.println(description + " playing track " + currentTrack);
        }
    }
    public void stop() {
        currentTrack = 0;
        System.out.println(description + " stopped");
    }
                      
    public void pause() {
        System.out.println(description + " paused \"" + title + "\"");
    }
                      
    public String toString() {
        return description;
    }
}

// TheaterLights.java
public class TheaterLights {
    String description;
                     
    public TheaterLights(String description) {
        this.description = description;
    }
                   
    public void on() {
        System.out.println(description + " on");
    }
                   
    public void off() {
        System.out.println(description + " off");
    }
                   
    public void dim(int level) {
        System.out.println(description + " dimming to " + level  + "%");
    }
                    
        public String toString() {
                return description;
        }
}

// DvdPlayer.java
public class DvdPlayer {
    String description;
    int currentTrack;
    Amplifier amplifier;
    String movie;
                  
    public DvdPlayer(String description, Amplifier amplifier) {
        this.description = description;
        this.amplifier = amplifier;
    }
               
    public void on() {
        System.out.println(description + " on");
    }
               
    public void off() {
        System.out.println(description + " off");
    }
        public void eject() {
        movie = null;
                System.out.println(description + " eject");
        }
               
    public void play(String movie) {
        this.movie = movie;
        currentTrack = 0;
        System.out.println(description + " playing \"" + movie + "\"");
    }
    public void play(int track) {
        if (movie == null) {
            System.out.println(description + " can't play track " + track + " no dvd inserted");
        } else {
            currentTrack = track;
            System.out.println(description + " playing track " + currentTrack + " of \"" + movie + "\"");
        }
    }
    public void stop() {
        currentTrack = 0;
        System.out.println(description + " stopped \"" + movie + "\"");
    }
               
    public void pause() {
        System.out.println(description + " paused \"" + movie + "\"");
    }
    public void setTwoChannelAudio() {
        System.out.println(description + " set two channel audio");
    }
               
    public void setSurroundAudio() {
        System.out.println(description + " set surround audio");
    }
               
    public String toString() {
        return description;
    }
}

// Projector.java
public class Projector {
    String description;
    DvdPlayer dvdPlayer;
            
    public Projector(String description, DvdPlayer dvdPlayer) {
        this.description = description;
        this.dvdPlayer = dvdPlayer;
    }
         
    public void on() {
        System.out.println(description + " on");
    }
         
    public void off() {
        System.out.println(description + " off");
    }
    public void wideScreenMode() {
        System.out.println(description + " in widescreen mode (16x9 aspect ratio)");
    }
    public void tvMode() {
        System.out.println(description + " in tv mode (4x3 aspect ratio)");
    }
          
        public String toString() {
                return description;
        }
}

測試代碼

// HomeTheaterTestDrive.java
public class HomeTheaterTestDrive {
    public static void main(String[] args) {
        Amplifier amp = new Amplifier("Top-O-Line Amplifier");
        Tuner tuner = new Tuner("Top-O-Line AM/FM Tuner", amp);
        DvdPlayer dvd = new DvdPlayer("Top-O-Line DVD Player", amp);
        CdPlayer cd = new CdPlayer("Top-O-Line CD Player", amp);
        Projector projector = new Projector("Top-O-Line Projector", dvd);
        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, dvd, cd,
                        projector, screen, lights, popper);
      
        homeTheater.watchMovie("Raiders of the Lost Ark");
        homeTheater.endMovie();
    }
}

運行效果