求大神指点。书上非常简单的一个程序 ，自己敲进去显示不出书上的功能。
package picture;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class JCheckDemo {
JCheckBox CB1,CB2,CB4,CB8;
StringBuffer choices;
JLabel display;
JPanel checkPanel;
public JCheckDemo(){
CB1=new JCheckBox("1");
CB1.setMnemonic(KeyEvent.VK_4);
CB1.setSelected(true);

CB2=new JCheckBox("2");
CB2.setMnemonic(KeyEvent.VK_3);
CB2.setSelected(true);

CB4=new JCheckBox("4");
CB4.setMnemonic(KeyEvent.VK_2);
CB4.setSelected(true);

CB8=new JCheckBox("8");
CB8.setMnemonic(KeyEvent.VK_1);
CB8.setSelected(true);

CheckBoxListener myListener=new CheckBoxListener();

CB1.addItemListener(myListener);
CB2.addItemListener(myListener);
CB4.addItemListener(myListener);
CB8.addItemListener(myListener);

choices=new StringBuffer("8421");
display=new JLabel(choices.toString());

checkPanel=new JPanel();
checkPanel.setLayout(new GridLayout(0,1));
checkPanel.add(CB1);
checkPanel.add(CB2);
checkPanel.add(CB4);
checkPanel.add(CB8);
}
class CheckBoxListener implements ItemListener
{
public void itenStateChanged(ItemEvent e){
int index=0;
char c='-';
JCheckBox src=(JCheckBox)e.getItemSelectable();
if(src==CB8){index=0;c='8';}
if(src==CB4){index=1;c='4';}
if(src==CB2){index=2;c='2';}
if(src==CB1){index=3;c='1';}
if(e.getStateChange()==ItemEvent.DESELECTED)
c='-';
choices.setCharAt(index ,c);
display.setText(choices.toString());

}

public void itemStateChanged(ItemEvent e) {
throw new UnsupportedOperationException("Not supported yet.");
}//这段代码是 编译器自动生成的，说什么抽象类，本来书上的程序没有这段
}
public static void main(String[]args){
JCheckDemo JCD=new JCheckDemo();
JFrame Frame=new JFrame("JCheckBox使用实例");
Frame.getContentPane().setLayout(new FlowLayout());
Frame.getContentPane().add(JCD.checkPanel);
Frame.getContentPane().add(JCD.display);
Frame.pack();
Frame.setVisible(true);

}
}

功能简介：
开始窗口显示“8421”按下一个 复选按钮，相应的数字变为“-”
这是书上的介绍，但我运行，功能不显示。
本人刚学JAVA菜鸟，用netbeans编译器
不胜感谢

[解决办法]
你原来的拼写错了，itenStateChanged 改成 itemStateChanged然后把那个自动生成的代码注解掉

Java code

import javax.swing.*;import java.awt.*;import java.awt.event.*;public class JCheckDemo {    JCheckBox CB1,CB2,CB4,CB8;    StringBuffer choices;    JLabel display;    JPanel checkPanel;    public JCheckDemo(){        CB1=new JCheckBox("1");        CB1.setMnemonic(KeyEvent.VK_4);        CB1.setSelected(true);        CB2=new JCheckBox("2");        CB2.setMnemonic(KeyEvent.VK_3);        CB2.setSelected(true);        CB4=new JCheckBox("4");        CB4.setMnemonic(KeyEvent.VK_2);        CB4.setSelected(true);        CB8=new JCheckBox("8");        CB8.setMnemonic(KeyEvent.VK_1);        CB8.setSelected(true);        CheckBoxListener myListener=new CheckBoxListener();        CB1.addItemListener(myListener);        CB2.addItemListener(myListener);        CB4.addItemListener(myListener);        CB8.addItemListener(myListener);        choices=new StringBuffer("8421");        display=new JLabel(choices.toString());        checkPanel=new JPanel();        checkPanel.setLayout(new GridLayout(0,1));        checkPanel.add(CB1);        checkPanel.add(CB2);        checkPanel.add(CB4);        checkPanel.add(CB8);    }    class CheckBoxListener implements ItemListener    {        public void itemStateChanged(ItemEvent e){ //你原的拼有            int index=0;            char c='-';            JCheckBox src=(JCheckBox)e.getItemSelectable();            if(src==CB8){index=0;c='8';}            if(src==CB4){index=1;c='4';}            if(src==CB2){index=2;c='2';}            if(src==CB1){index=3;c='1';}            if(e.getStateChange()==ItemEvent.DESELECTED)                c='-';            choices.setCharAt(index ,c);            display.setText(choices.toString());        }//        public void itemStateChanged(ItemEvent e) {//            throw new UnsupportedOperationException("Not supported yet.");//        }//这段代码是 编译器自动生成的，说什么抽象类，本来书上的程序没有这段    }    public static void main(String[]args){        JCheckDemo JCD=new JCheckDemo();        JFrame frame=new JFrame("JCheckBox使用实例");        frame.getContentPane().setLayout(new FlowLayout());        frame.getContentPane().add(JCD.checkPanel);        frame.getContentPane().add(JCD.display);        frame.pack();        frame.setVisible(true);        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);    }}