很有用的观察者设计模式

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import java.util.Observable;

public 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();          //设置变化点

        super.notifyObservers(price);  //发出变化通知

        this.price = price;

    }

    @Override

    public String toString() {

        return "房子的价格为:" + price ;

    }

}

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import java.util.Observable;

import java.util.Observer;

public class Buyer implements Observer{

    private String name;

    public Buyer(String name) {

        this.name = name;

    }

    @Override

    public void update(Observable observable, Object object) {

        if (object instanceof Float) {

            System.out.print(this.name + "观察到价格变化：");

            System.out.println(((Float)object).floatValue());

        }

    }

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public class TestMain {

    /**

     * @param args

     */

    public static void main(String[] args) {

        House house = new House(1000f);

        Buyer b1 = new Buyer("A");

        Buyer b2 = new Buyer("B");

        Buyer b3 = new Buyer("C");

        house.addObserver(b1);

        house.addObserver(b2);

        house.addObserver(b3);

        System.out.println(house);

        house.setPrice(6000.0f);

        System.out.println(house);

    }

}