Java中常用的设计模式之观察者模式详解

package com.asurplus.common.observe;

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

package com.asurplus.common.observe;
import lombok.extern.slf4j.Slf4j;
@Slf4j
public class Observer1 extends Observer {
    public Observer1(Subject subject) {
        this.subject = subject;
        this.subject.attach(this);
    }
    @Override
    public void update() {
        log.info("观察者 1 收到通知：{}", this.subject.getState());
    }
}

package com.asurplus.common.observe;
import lombok.extern.slf4j.Slf4j;
@Slf4j
public class Observer2 extends Observer {
    public Observer2(Subject subject) {
        this.subject = subject;
        this.subject.attach(this);
    }
    @Override
    public void update() {
        log.info("观察者 2 收到通知：{}", this.subject.getState());
    }
}

package com.asurplus.common.observe;
import lombok.extern.slf4j.Slf4j;
@Slf4j
public class Observer3 extends Observer {
    public Observer3(Subject subject) {
        this.subject = subject;
        this.subject.attach(this);
    }
    @Override
    public void update() {
        log.info("观察者 3 收到通知：{}", this.subject.getState());
    }
}

package com.asurplus.common.observe;
import java.util.ArrayList;
import java.util.List;

public class Subject {
    
    private List<Observer> observers = new ArrayList<>();
    
    private int state;
    public int getState() {
        return state;
    }
    
    public void setState(int state) {
        this.state = state;
        // 通知所有观察者
        notifyAllObservers();
    }
    
    public void attach(Observer observer) {
        observers.add(observer);
    }
    
    public void notifyAllObservers() {
        for (Observer observer : observers) {
            observer.update();
        }
    }
}

package com.asurplus.common.observe;
public class TestMain {
    public static void main(String[] args) {
        // 创建主题
        Subject subject = new Subject();
        // 添加观察者
        new Observer1(subject);
        new Observer2(subject);
        new Observer3(subject);
        // 改变标志
        subject.setState(10);
    }
}