设计模式——观察者模式

现在安卓开发需要用到RxJava Retrofit，而RxJava是观察者模式，于是去看了下观察者模式是怎么个回事。

大概意思应该是 A监视B 但是A并非实时监视B，而是给B注册一个事件，在B发生某种动作（事件）之后通知A，然后A再做出相应的响应。

代码：

ObServer：

package com.example.z.tabview.test.gczms;

/**
 * 抽象观察者
 * Created by Z on 2017/6/6.
 */

public interface ObServer {

    void update(Subject subject);
}

ConcreteObServer：

package com.example.z.tabview.test.gczms;

/**
 * 具体的观察者
 * Created by Z on 2017/6/6.
 */

public class ConcreteObServer implements ObServer {

    private int state;

    @Override
    public void update(Subject subject) {
        this.state = ((ConcreteSubject) subject).getState();
    }

    public int getState() {
        return state;
    }

    public void setState(int state) {
        this.state = state;
    }
}

Subject：

package com.example.z.tabview.test.gczms;

import java.util.ArrayList;
import java.util.List;

/**
 * 抽象主题对象
 * Created by Z on 2017/6/6.
 */

public class Subject {
    //保存该主题下的所有观察者
    protected List<ObServer> listObserver = new ArrayList<>();

    public void registerObserver(ObServer obServer) {
        listObserver.add(obServer);
    }

    public void removeObserver(ObServer obServer) {
        listObserver.remove(obServer);
    }

    public void notifyAllObserver() {

        for (ObServer obServer : listObserver) {
            obServer.update(this);
        }

    }

}

ConcreteSubject：

package com.example.z.tabview.test.gczms;

/**
 * 具体主题对象
 * Created by Z on 2017/6/6.
 */

public class ConcreteSubject extends Subject {
    private int state;

    public int getState() {
        return state;
    }

    public void setState(int state) {
        this.state = state;
        this.notifyAllObserver();
    }
}

Test：

package com.example.z.tabview.test.gczms;

/**
 * 测试方法
 * Created by Z on 2017/6/6.
 */

public class Test {


    public static void main(String[] args) {
        ConcreteSubject cs = new ConcreteSubject();

        ConcreteObServer cos1 = new ConcreteObServer();
        ConcreteObServer cos2 = new ConcreteObServer();
        ConcreteObServer cos3 = new ConcreteObServer();

        cos1.setState(10);
        cos2.setState(20);
        cos3.setState(30);


        System.out.println(cos1.getState());
        System.out.println(cos2.getState());
        System.out.println(cos3.getState());

        System.out.println("----------修改后的状态----------");

        cs.registerObserver(cos1);
        cs.registerObserver(cos2);
        cs.registerObserver(cos3);

        cs.setState(100);

        System.out.println(cos1.getState());
        System.out.println(cos2.getState());
        System.out.println(cos3.getState());
    }


}

输出：

10
20
30
----------修改后的状态----------
100
100
100