设计模式_Observable与Observer

一.基本概念
   java.util.Observable 被观察者类，需要继承这个类
   java.util.Observer 观察者类，需要实现这个接口中的update()方法

二.举例 Door2
   属性 name 和status 改变，被监管
1.Door2

import java.util.Observable;

//被监管对象
public class Door2 extends Observable {
    private String state = "";
    private String name = "";

    public void setState(String newValue) {
        if (state != newValue) {
            this.state = newValue;
            // 标记此 Observable对象为已改变的对象
            setChanged();
            // 通知所有观察者
            notifyObservers("state");
        }
    }

    public void setName(String newValue) {
        if (name != newValue) {
            this.name = newValue;
            // 标记此 Observable对象为已改变的对象
            setChanged();
            // 通知所有观察者
            notifyObservers("name");
        }
    }
    //////////////////////////////////////////
    public String getName() {
        return name;
    }

    public String getState() {
        return state;
    }
}

2.被监管对象
   Door2StateObserver

import java.util.Observable;
import java.util.Observer;

public class Door2StateObserver implements Observer {

    @Override
    public void update(Observable o, Object arg) {
        Door2 door2 = (Door2) o;
        if (!arg.toString().equalsIgnoreCase("state")) {
            return;
        }
        switch (door2.getState()) { // 使用Java 7的switch语句对string的判断支持
        case "open":
            System.out.println("门打开");
            break;
        case "close":
            System.out.println("门关闭");
            break;
        }
    }
}

Door2NameObserver

import java.util.Observable;
import java.util.Observer;

public class Door2NameObserver implements Observer {

    @Override
    public void update(Observable o, Object arg) {
        Door2 door2 = (Door2) o;
        if (!arg.toString().equalsIgnoreCase("name")) {
            return;
        }
        System.out.println("I got a new name,named \"" + door2.getName() + "\"");
    }
}

3.Door2Test

public class Door2Test {
    public static void main(String[] args) {

        Door2 door = new Door2();
        Observer stateListener = new Door2StateObserver();
        door.addObserver(stateListener);
        // 开门
        door.setState("open");
        System.out.println("我已经进来了");
        // 关门
        door.setState("close");

        //
        Observer nameListener = new Door2NameObserver();
        door.addObserver(nameListener);
        door.setName("dengzy");
    }
}