之前我们利用自定义的方式去实现了观察者模式(https://blog.csdn.net/m0_37618340/article/details/82942857),其实在Java中为我们提供了这样的类和接口,分别是:
Observerable类和Observer接口
接下来我们用给定的类实现观察者模式:
首先我们创建目标对象(继承Observable类):
package com.pmj.observer2;
import java.util.Observable;
/**
* 目标对象
* @author PP_boy
*
*/
public class ConCreateSubject extends Observable{
private int state;
public void set(int s) {
this.state = s;//目标对象的状态发生了改变
setChanged();//表示目标对象已经做了更改
notifyObservers(state);//通知所有观察者
}
public int getState() {
return state;
}
public void setState(int state) {
this.state = state;
}
}
然后我们创建观察者对象(实现Observer接口)
package com.pmj.observer2;
import java.util.Observable;
import java.util.Observer;
public class ObserverA implements Observer{
private int myState;
@Override
public void update(Observable o, Object arg) {
myState = ((ConCreateSubject)o).getState();
}
public int getMyState() {
return myState;
}
public void setMyState(int myState) {
this.myState = myState;
}
}
测试类:
package com.pmj.observer2;
public class Client {
public static void main(String[] args) {
// 创建目标对象
ConCreateSubject subject = new ConCreateSubject();
// 创建多个观察者
ObserverA obs1 = new ObserverA();
ObserverA obs2 = new ObserverA();
ObserverA obs3 = new ObserverA();
// 讲观察者放入到目标对象的观察者队伍中
subject.addObserver(obs1);
subject.addObserver(obs2);
subject.addObserver(obs3);
// 修改目标对象的状态
subject.setState(30);
// 查看观察者的状态是否也随着变化
System.out.println(obs1.getMyState());
System.out.println(obs2.getMyState());
System.out.println(obs3.getMyState());
}
}