设计模式系列之观察者模式

本文从jdk内置的观察者模式来介绍观察者模式。 业务场景：当老师进门的时候，班长带头叫“老师好”，然后全班同学一起交“老师好” 因为太简单，直接上代码

班长继承自Observable

package Observer;

import java.util.Observable;
import java.util.Observer;

public class Monitor extends Observable{
    public Monitor() {
        super();
    }

    @Override
    public synchronized void addObserver(Observer o) {
        super.addObserver(o);
    }

    @Override
    public synchronized void deleteObserver(Observer o) {
        super.deleteObserver(o);
    }

    @Override
    public void notifyObservers() {
        super.notifyObservers();
    }

    @Override
    public void notifyObservers(Object arg) {
        super.notifyObservers(arg);
    }

    @Override
    public synchronized void deleteObservers() {
        super.deleteObservers();
    }

    @Override
    protected synchronized void setChanged() {
        super.setChanged();
    }

    @Override
    protected synchronized void clearChanged() {
        super.clearChanged();
    }

    @Override
    public synchronized boolean hasChanged() {
        return super.hasChanged();
    }

    @Override
    public synchronized int countObservers() {
        return super.countObservers();
    }
}

学生继承自Observer

package Observer;

import java.util.Observable;
import java.util.Observer;

/**
 * 观察者
 */
public class Student implements Observer{
    String name;

    public Student() {
    }
    public Student(String name) {
        this.name = name;
    }

    @Override
    public void update(Observable o, Object arg) {
        System.out.println("学生" + this.name + "说老师好");
    }
}

测试类：

package Observer;

public class Maintest {

    public static void main(String[] args) {
        Monitor monitor = new Monitor();

        Student student1 = new Student("小明");
        monitor.addObserver(student1);

        Student student2 = new Student("小蓝");
        monitor.addObserver(student2);

        Student student3 = new Student("小白");
        monitor.addObserver(student3);

        // 只有设置了这个值才进行通知
        monitor.setChanged();
        // 班长通知所有学生老师来了，起立
        monitor.notifyObservers();
    }
}

结果：

学生小白说老师好
学生小蓝说老师好
学生小明说老师好