java之swing实现复选框的方法

import java.awt.*;import javax.swing.*;import java.awt.event.*;public class test extends JAppletimplements ItemListener{  JTextField jtf;  public void init(){    Container contentPane = getContentPane();    contentPane.setLayout(new FlowLayout());    ImageIcon a1 = new ImageIcon("D:/data/Images/6.gif");    ImageIcon a2 = new ImageIcon("D:/data/Images/7.gif");    ImageIcon a3 = new ImageIcon("D:/data/Images/8.gif");    JCheckBox cb = new JCheckBox("C", a1);    cb.setRolloverIcon(a2);    cb.setSelectedIcon(a3);    cb.addItemListener(this);    contentPane.add(cb);    cb = new JCheckBox("C++", a1);    cb.setRolloverIcon(a2);    cb.setSelectedIcon(a3);    cb.addItemListener(this);    contentPane.add(cb);    cb = new JCheckBox("java", a1);    cb.setRolloverIcon(a2);    cb.setSelectedIcon(a3);    cb.addItemListener(this);    contentPane.add(cb);    jtf = new JTextField(15);    contentPane.add(jtf);  }  public void itemStateChanged(ItemEvent ie){    JCheckBox cb = (JCheckBox)ie.getItem();    jtf.setText(cb.getText());  }}