Java开发网 - 为什么运行结果会是这样？

Topic: 为什么运行结果会是这样？

1.为什么运行结果会是这样？

Posted by: zhjdenis
Posted on: 2007-10-03 20:38

使用限制属性，运行正常，但是为什么第二次由于属性被拒绝后连续打印了两个
“property: weightwill be changed”？
运行结果如下
property: weightwill be changed
bean's value: weight: 20
second change:
property: weightwill be changed
property: weightwill be changed
property: weight is veto
bean's value: weight: 20

//以下是代码
package 限制属性;
import java.beans.*;
public class Mybean {
private int weight;
private transient VetoableChangeSupport veto=new VetoableChangeSupport(this);
public int getweight()
{
   return weight;
}
public void setweight(int weight) throws java.beans.PropertyVetoException
{
   int oldweight=this.weight;
   veto.fireVetoableChange("weight",new Integer(oldweight),new Integer(weight));
   this.weight=weight;
}
public String tostring()
{
   String s="bean's value: ";
   s=s+"weight: "+weight;
   return s;
}
public synchronized void add(VetoableChangeListener x)
{
  veto.addVetoableChangeListener(x);
}
}
//以下是主测试程序代码
package 限制属性;
import java.beans.*;
public class Propertydemo {
  public static void main(String[] args) {
    // TODO Auto-generated method stub
Mybean bean1=new Mybean();
bean1.add(new Myvetochangelistener());
System.out.println(bean1.tostring());
System.out.println("first change: ");
try
{
  bean1.setweight(20);
}
catch(PropertyVetoException ex)
{
  System.out.println(ex.getMessage());
}
System.out.println(bean1.tostring());
System.out.println("second change: ");
try
{
  bean1.setweight(150);
}
catch(PropertyVetoException ex1)
{
  System.out.println(ex1.getMessage());
}
System.out.println(bean1.tostring());
  }

}
//以下是否决监听器的代码
package 限制属性;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyVetoException;
import java.beans.VetoableChangeListener;
public class Myvetochangelistener implements VetoableChangeListener {

  public void vetoableChange(PropertyChangeEvent y)throws PropertyVetoException
  {
   System.out.println("property: "+y.getPropertyName()+" will be changed");
   if(((Integer)y.getNewValue()).intValue()>100)
   {
     throw new PropertyVetoException("property: "+y.getPropertyName()+" is veto",y);
   }
  }


}