观察者模式

1.观察者 Observer 例如客户

2.被观察者 Observable 例如 商品

3.被观察者基础Observable 

public class House extends Observable {
    private int price;

    public int getPrice() {
        return price;
    }

    public House(int price){
        this.price = price;
    }

    public void setPrice(int price) {
        if (price!=this.price){
            this.price = price;
            setChanged();
　　　　　　　//传入的price 会再update方法里收到 即arg
            notifyObservers(price);
        }
    }
}

4.观察者实现Observer

public class People implements Observer {
    @Override
    public void update(Observable o, Object arg) {
        if (o instanceof House){
            System.out.println("房价为"+arg);
        }
    }
}

5.测试类

public static void main(String[] args) {
        House house = new House(100);
        People A = new People();
        People B = new People();
        People C = new People();
        //添加观察者
        house.addObserver(A);
        house.addObserver(B);
        house.addObserver(C);
        //取消观察者
        house.deleteObserver(A);
        house.setPrice(1001);
    }