外观模式

1.外观模式

提供了一个统一的接口,用来访问子系统中的一群接口.外观定义了一个高层接口,让子系统更容易使用.

2代码实现

比如我们要看电影,需要进行很多操作,播放dvd,准备好爆米花,打开灯光.播放屏幕等....

我们先定义扩音器,播放器等底层组件

package appearance;

public class Amplifer {
    void on() {
        System.out.println("amp on");
    }
    void off() {
        System.out.println("amp off");
    }
    void setDvd(DvdPlayer dvd) {
        System.out.println("amp setDvd");
    }
    
    void setSurroundSound(DvdPlayer dvd) {
        System.out.println("amp setDvd");
    }
    
    void setVolume(int i) {
        System.out.println("amp surroundSound "+i);
    }
    
}

package appearance;

public class CdPlayer {

}

package appearance;

public class DvdPlayer {
    public void on() {
        System.out.println("Dvdplayer on");
    }
    public void play(String movie) {
        System.out.println("Dvdplayer play " + movie);
    }
    public void stop() {
        System.out.println("Dvdplayer stop");
    }
    public void eject() {
        System.out.println("Dvdplayer eject");
    }
    public void off() {
        System.out.println("Dvdplayer off");
    }
}

package appearance;

public class PopcornPopper {
    void on () {
        System.out.println(" PopcornPopper on ");
    }
    void off () {
        System.out.println(" PopcornPopper off ");
    }
    void pop () {
        System.out.println(" PopcornPopper pop ");
    }
}

package appearance;

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

package appearance;

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

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

package appearance;

public class TheaterLights {
    public void dim(int i) {
        System.out.println("Threater lights dim " + i);
    }
    public void on() {
        System.out.println("Threater lights on " );
    }
}

package appearance;

public class Tuner {

}

虽然我们可以直接调用这些组件,但是把这些组件封装到一个统一的接口中调用会更容易使用,而且调用者和子系统之间的耦合也通过外观模式解耦了,调用者依赖的不是底层组件,而是通过底层组件组合而成的外观模式组件.

接下来就定义关键的外观模式组件

package appearance;

public class HomeTheaterFacade {
    Amplifer amp;//扩音器
    Tuner tuner;//调音器
    DvdPlayer dvd;//dvd播放器
    CdPlayer cd;//cd播放器
    Projector projector;//投影机
    TheaterLights lights;//剧场灯光
    Screen screen;//屏幕
    PopcornPopper popper;//爆米花
    public HomeTheaterFacade(Amplifer amp, Tuner tuner, DvdPlayer dvd, CdPlayer cd, Projector projector,
            TheaterLights lights, Screen screen, PopcornPopper popper) {
        super();
        this.amp = amp;
        this.tuner = tuner;
        this.dvd = dvd;
        this.cd = cd;
        this.projector = projector;
        this.lights = lights;
        this.screen = screen;
        this.popper = popper;
    }
    public void watchMovie(String movie) {
        System.out.println("Watch movie....");
        popper.on();
        popper.pop();
        lights.dim(10);
        screen.down();
        projector.on();
        projector.wideScreenMode();
        amp.on();
        amp.setDvd(new DvdPlayer());
        amp.setVolume(5);
        dvd.on();
        dvd.play(movie);
    }
    public void endWatchMovie() {
        System.out.println("Movie end....");
        popper.off();
        lights.on();
        screen.up();
        projector.off();
        amp.off();
        dvd.stop();
        dvd.eject();
        dvd.off();
    }
}

老生常谈,还是通过组合的方式来实现外观模式,怪不得第一个模式要讲策略模式,因为组合真的是构成了设计模式很大一部分.

3.总结

外观模式主要是把各个子系统的功能封装提供一个统一的子系统,其实平常编码也经常用,只是没有定义它为外观模式.