观察者模式demo

主题类

package demo;

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

public class Subject {

    private List observers = new ArrayList();
    private int state;

    public int getState() {
        return state;
    }

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

    public void attach(Observer observer){
        observers.add(observer);
    }

    public void notifyAllObservers(){
        for (Observer observer : observers) {
            observer.update();
        }
    }
}

观察者抽象类

package demo;

public abstract class Observer {
    protected Subject subject;
    public abstract void update();
}

观察者子类A

package demo;

public class AObserver extends Observer{

    public AObserver(Subject subject){
        this.subject = subject;
        subject.attach(this);
    }

    @Override
    public void update() {
        System.out.println( "观察者A 更新了状态: "+subject.getState());
    }
}

观察者子类B

package demo;

public class BObserver extends Observer{

    public BObserver(Subject subject){
        this.subject = subject;
        subject.attach(this);
    }

    @Override
    public void update() {
        System.out.println( "观察者B 更新了状态: "+subject.getState());
    }
}

测试类

package demo;

public class demo1 {
    public static void main(String[] args) {
        Subject subject = new Subject();

        new AObserver(subject);
        new BObserver(subject);

        subject.setState(8);
        System.out.println("---------分割线---------");
        subject.setState(88);
    }
}

运行结果

观察者A 更新了状态: 8
观察者B 更新了状态: 8
---------分割线---------
观察者A 更新了状态: 88
观察者B 更新了状态: 88