简谈设计模式之外观模式

外观模式是一种结构性设计模式, 通过为复杂的子系统提供一个统一的接口, 使得子系统更容易使用.

外观模式结构

外观: 提供一个高层接口, 供客户使用, 它知道哪些子系统负责处理请求, 并将客户的请求委派给适当的子系统
子系统类: 实现子系统的功能, 处理由外观指派的任务

外观模式实现

假设有一个复杂的家庭影院系统, 包括DVD, 投影仪, 音响, 灯光等系统, 可以通过外观模式来模拟这个系统的实现

class DVDPlayer {
    public void on() {
        System.out.println("DVD Player is on");
    }
    
    public void play(String movie) {
        System.out.println("Playing " + movie);
    }
    
    public void off() {
        System.out.println("DVD Player is off");
    }
}

class Projector {
    public void on() {
        System.out.println("Projector is on");
    }
    
    public void off() {
        System.out.println("Projector is off");
    }
}

class Sound {
    public void on() {
        System.out.println("Sound is on");
    }
    
    public void setVolume(int level) {
        System.out.println("Setting sound volume to " + level);
    }
    
    public void off() {
        System.out.println("Sound is off");
    }
}

class Light {
    public void on() {
        System.out.println("Lights are on");
    }
    
    public void dim(int level) {
        System.out.println("Dimming lights to " + level + "%");
    }
    
    public void off() {
        System.out.println("Lights are off");
    }
}

class HomeTheaterFacade {
    private DVDPlayer dvdPlayer;
    private Projector projector;
    private SoundSystem soundSystem;
    private Light light;

    public HomeTheaterFacade(DVDPlayer dvdPlayer, Projector projector, SoundSystem soundSystem, Light light) {
        this.dvdPlayer = dvdPlayer;
        this.projector = projector;
        this.soundSystem = soundSystem;
        this.light = light;
    }

    public void watchMovie(String movie) {
        System.out.println("Get ready to watch a movie...");
        light.dim(10);
        projector.on();
        soundSystem.on();
        soundSystem.setVolume(5);
        dvdPlayer.on();
        dvdPlayer.play(movie);
    }

    public void endMovie() {
        System.out.println("Shutting down movie theater...");
        dvdPlayer.off();
        soundSystem.off();
        projector.off();
        light.on();
    }
}

public class Client {
    public static void main(String[] args) {
        DVDPlayer dvdPlayer = new DVDPlayer();
        Projector projector = new Projector();
        SoundSystem soundSystem = new SoundSystem();
        Light light = new Light();

        HomeTheaterFacade homeTheater = new HomeTheaterFacade(dvdPlayer, projector, soundSystem, light);
        homeTheater.watchMovie("Inception");
        homeTheater.endMovie();
    }
}