一个Bound属性是指当该种属性的值发生变化时，要通知其它的对象。每次属性值改变时，这种属性就点火一个PropertyChange事件(在Java程序中，事件也是一个对象)。事件中封装了属性名、属性的原值、属性变化后的新值。这种事件是传递到其它的Bean，至于接收事件的Bean应做什么动作由其自己定义。

股价是经常变化的。

测试代码：

package com.beans;

import java.beans.PropertyChangeEvent;

import java.beans.PropertyChangeListener;

import java.beans.PropertyChangeSupport;

import java.util.Random;

import junit.framework.TestCase;

import static java.lang.System.out;

public class TestPropertyChange extends TestCase {

public void testPropertyChange() {

StockPrice stockPrice = new StockPrice();

StockPriceListener listener = new StockPriceListener();

stockPrice.addPropertyChangeListener(listener);

Random random = new Random();

for (int i = 0; i < 10; i++) {

stockPrice.setPrice(random.nextInt(100));

}

}

static class StockPrice {

private int price;

private PropertyChangeSupport support = new PropertyChangeSupport(this);

public int getPrice() {

return price;

}

public void setPrice(int price) {

support.firePropertyChange("price", this.price, price);

this.price = price;

}

public void addPropertyChangeListener(PropertyChangeListener listener) {

support.addPropertyChangeListener(listener);

}

public void removePropertyChangeListener(PropertyChangeListener listener) {

support.removePropertyChangeListener(listener);

}

}

static class StockPriceListener implements PropertyChangeListener {

@Override

public void propertyChange(PropertyChangeEvent evt) {

out.println(evt.getOldValue() + "->" + evt.getNewValue());

}

}

}