java 观察者模式设计方法

import java.util.Observable;
import java.util.Observer;
class House extends Observable {
    private float price;
    public House(float price){
        this.price=price;
    }
    public float getPrice(){
        return price;
    }
    public void setPrice(float price){
        super.setChanged();
        super.notifyObservers(price);
        this.price=price;
    }
    public String toString(){
        return "房子价格："+this.price;
    }
}
class HousePriceObserver implements Observer{
    private String name;
    public HousePriceObserver(String name){
        this.name=name;
    }
    public void update(Observable obj,Object arg){
        if(arg instanceof Float){
            System.out.print(this.name+"观察者看到的价格:");
            System.out.println(((Float) arg).floatValue());
        }
    }
}
public class ObserDemo {
    public static void main(String[] args) {
        House h=new House(1000000);
        HousePriceObserver hp1=new HousePriceObserver("A");
        HousePriceObserver hp2=new HousePriceObserver("B");
        HousePriceObserver hp3=new HousePriceObserver("C");
        h.addObserver(hp1);
        h.addObserver(hp2);
        h.addObserver(hp3);
        System.out.println(h);
        h.setPrice(6666);
        System.out.println(h);
    }
}