奇怪问题！！！！求高手解答！！！

[xiaoshu97]

关于JList的监听问题
如下代码：
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
import java.net.*;
import java.io.*;
import java.util.*;
public class sss extends JFrame
{
JTextField b1=null;
JComboBox b21;
JList list;
public sss()
{
getContentPane().setLayout(new FlowLayout());
b1=new JTextField(20);
Vector v=new Vector();
v.addElement(new String("adsfa"));
v.addElement(new String("adsfa1"));
v.addElement(new String("adsfa2"));
v.addElement(new String("adsfa3"));
v.addElement(new String("adsfa4"));
v.addElement(new String("adsfa5"));
list=new JList(v);
list.addListSelectionListener(new ListSelectionListener()
{
public void valueChanged(ListSelectionEvent ee)
{
b21.addItem(list.getSelectedValue());
}
});
/*list.addFocusListener(new FocusListener()
{
public void addFocusListener(FocusEvent ee);
{
b21.addItem(list.getSelectedValue());
}
public void focusLost(FocusEvent e)
{
}

}
);*/
b21=new JComboBox();


b1.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent ee)
{
System.out.println(""+b1.getText());
System.out.println(""+b21.getSelectedItem());;
}
});
getContentPane().add(b1);
getContentPane().add(b21);
getContentPane().add(list);
setSize(500,500);
show();
}
public static void main(String atgs[])
{
sss ss=new sss();

}
}
为什么在这我点以下Jlist在JComoBox中添加了2个所点的东西呢？？？？？？？？？
望知道的指点小弟一下！！！

[sijuven]

是不是注册了两次监听器，

[xiaoshu97]

没，这些就是所有的代码了。