观察者设计模式介绍

被观察者（事件源）

package com.dwz.concurrency2.chapter4;

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

public class Subject {
    private List<Observer> observers = new ArrayList<>();
    
    private int state;
    
    public int getState() {
        return this.state;
    }
    
    public void setState(int state) {
        if(state == this.state) {
            return;
        }
        this.state = state;
        notifyAllObserver();
    }
    
    public void attach(Observer observer) {
        observers.add(observer);
    }
    
    private void notifyAllObserver() {
        observers.stream().forEach(Observer::update);
    }
}

观察者抽象类

package com.dwz.concurrency2.chapter4;

public abstract class Observer {
    protected Subject subject;
    
    public Observer(Subject subject) {
        this.subject = subject;
        this.subject.attach(this);
    }
    
    public abstract void update();
}

观察者1-二进制观察者

package com.dwz.concurrency2.chapter4;

public class BinaryObserver extends Observer {
    
    public BinaryObserver(Subject subject) {
        super(subject);
    }
    
    @Override
    public void update() {
        System.out.println("Binary String:" + Integer.toBinaryString(subject.getState()));
    }
    
}

观察者2-八进制观察者

package com.dwz.concurrency2.chapter4;

public class OctalObserver extends Observer {
    
    public OctalObserver(Subject subject) {
        super(subject);
    }
    
    @Override
    public void update() {
        System.out.println("Octal String:" + Integer.toOctalString(subject.getState()));
    }
}

测试类

package com.dwz.concurrency2.chapter4;

public class ObserverClient {
    public static void main(String[] args) {
        final Subject subject = new Subject();
        new BinaryObserver(subject);
        new OctalObserver(subject);
        System.out.println("==================");
        subject.setState(10);
        
        System.out.println("==================");
        subject.setState(10);
        
        System.out.println("==================");
        subject.setState(15);
    }
}