门面模式是对象的结构模式。
门面模式要求一个子系统的外部与其内部的通信必须通过一个统一的门面（Facade）对象进行。

何时使用？
1. 为一个复杂子系统提供一个简单接口
2. 子系统的独立性
3. 层次化结构

对象图示意：


1. com.cleversoft.designpatterns.facade.Alarm.java:
package com.cleversoft.designpatterns.facade;

public class Alarm {
    public void activate() {
        System.out.println("Activating the alarm.");
    }

    public void deactivate() {
        System.out.println("Deactivating the alarm.");
    }

    public void ring() {
        System.out.println("Ring the alarm.");
    }

    public void stopRing() {
        System.out.println("Stop the alarm.");
    }
}

2. com.cleversoft.designpatterns.facade.Camera.java:
package com.cleversoft.designpatterns.facade;

public class Camera {
    public void turnOn() {
        System.out.println("Turning on the camera.");
    }

    public void turnOff() {
        System.out.println("Turning off the camera.");
    }

    public void rotate(int degrees) {
        System.out.println("Rotating the camera by " + degrees + " degrees.");
    }
}

3. com.cleversoft.designpatterns.facade.Light.java:
package com.cleversoft.designpatterns.facade;

public class Light {
    public void turnOn() {
        System.out.println("Turning on the light.");
    }

    public void turnOff() {
        System.out.println("Turning off the light.");
    }

    public void changeBulb() {
        System.out.println("Changing the light-bulb.");
    }
}

4. com.cleversoft.designpatterns.facade.Sensor.java:
package com.cleversoft.designpatterns.facade;

public class Sensor {
    public void activate() {
        System.out.println("Activating on the sensor.");
    }

    public void deactivate() {
        System.out.println("Deactivating on the sensor.");
    }

    public void trigger() {
        System.out.println("The sensor has been triggered.");
    }
}

5. com.cleversoft.designpatterns.facade.SecurityFacade.java:
package com.cleversoft.designpatterns.facade;

public class SecurityFacade {
    private Camera camera1, camera2;

    private Light light1, light2, light3;

    private Sensor sensor;

    private Alarm alarm;

    public SecurityFacade() {
        camera1 = new Camera();
        camera2 = new Camera();
        light1 = new Light();
        light2 = new Light();
        light3 = new Light();
        sensor = new Sensor();
        alarm = new Alarm();
    }

    public void activate() {
        camera1.turnOn();
        camera2.turnOn();

        light1.turnOn();
        light2.turnOn();
        light3.turnOn();

        sensor.activate();
        alarm.activate();
    }

    public void deactivate() {
        camera1.turnOff();
        camera2.turnOff();

        light1.turnOff();
        light2.turnOff();
        light3.turnOff();

        sensor.deactivate();
        alarm.deactivate();
    }
}

6. com.cleversoft.designpatterns.facade.Client.java:
package com.cleversoft.designpatterns.facade;

public class Client {
    private static SecurityFacade security = new SecurityFacade();

    public static void main(String[] args) {
        security.activate();
    }
}


参考资料：
1. 《Java与模式》

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