Java 23中设计模式--观察者模式

package com.bjsxt.observer;

public interface Observer {
    void  update(Subject subject);
}

package com.bjsxt.observer;

public class ObserverA implements Observer {

    private int myState;   //myState需要跟目标对象的state值保持一致！
    
    
    @Override
    public void update(Subject subject) {
        myState = ((ConcreteSubject)subject).getState();
    }


    public int getMyState() {
        return myState;
    }
    public void setMyState(int myState) {
        this.myState = myState;
    }
    
    

}

package com.bjsxt.observer;

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

public class Subject {
    
    protected List<Observer> list = new ArrayList<Observer>();
    
    public void registerObserver(Observer obs){
        list.add(obs);
    }
    public void removeObserver(Observer obs){
        list.add(obs);
    }

    //通知所有的观察者更新状态
    public void notifyAllObservers(){
        for (Observer obs : list) {
            obs.update(this);
        }
    }
    
}

package com.bjsxt.observer;

public class ConcreteSubject extends Subject {
    
    private int state;

    public int getState() {
        return state;
    }

    public void setState(int state) {

        this.state = state;
        //主题对象(目标对象)值发生了变化，请通知所有的观察者
        this.notifyAllObservers();
    } 
    
    
    
    
    
}

package com.bjsxt.observer;

public class Client {
    public static void main(String[] args) {
        //目标对象
        ConcreteSubject subject = new ConcreteSubject();
        
        //创建多个观察者
        ObserverA  obs1 = new ObserverA();
        ObserverA  obs2 = new ObserverA();
        ObserverA  obs3 = new ObserverA();
        
        //将这三个观察者添加到subject对象的观察者队伍中
        subject.registerObserver(obs1);
        subject.registerObserver(obs2);
        subject.registerObserver(obs3);

        
        //改变subject的状态
        subject.setState(3000);
        System.out.println("########################");
        //我们看看，观察者的状态是不是也发生了变化
        System.out.println(obs1.getMyState());
        System.out.println(obs2.getMyState());
        System.out.println(obs3.getMyState());
        
        //改变subject的状态
        subject.setState(30);
        System.out.println("########################");
        //我们看看，观察者的状态是不是也发生了变化
        System.out.println(obs1.getMyState());
        System.out.println(obs2.getMyState());
        System.out.println(obs3.getMyState());
        
        
    }
}