观察者模式

1、定义被观察类，继承Observable

public class Observed extends Observable{
    private Integer num;

    public Observed() {
        super();
    }

    public Observed(Integer num) {
        super();
        this.num = num;
    }

    public Integer getNum() {
        return num;
    }

    public void setNum(Integer num) {
        super.setChanged();        //设置观察点
        super.notifyObservers(num);  //通知所有观察者
        this.num = num;
    }

    @Override
    public String toString() {
        return "Observed [num=" + num + "]";
    }
}

2、定义观察者，实现Observer接口

public class NumberObserver implements Observer{
    private String name;
    
    public NumberObserver(String name) {
        super();
        this.name = name;
    }

    @Override
    public void update(Observable o, Object arg) {
        if(arg instanceof Integer) {
            System.out.println(this.name + "观察到数量更新为：" + (Integer)arg);
        }
        
    }

}

3、测试

public class TestObserver {

    public static void main(String[] args) {
        Observed o = new Observed(100);
        NumberObserver no1 = new NumberObserver("A");
        NumberObserver no2 = new NumberObserver("B");
        NumberObserver no3 = new NumberObserver("C");
        o.addObserver(no1);
        o.addObserver(no2);
        o.addObserver(no3);
        System.out.println(o);
        o.setNum(666);
        System.out.println(o);
        
    }
}