java图形用户界面之下拉列表

package example_java;

import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;

import javax.naming.InitialContext;
import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;
class windowChoice extends JFrame implements ItemListener, ActionListener{
    JComboBox choice;
    JTextField text;
    JTextArea area;
    JButton add, del;
    public windowChoice() {
     init();
     setSize(400, 400);
     setVisible(true);
     setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
} 
      void init(){
          setLayout(new FlowLayout());
          choice = new JComboBox();
          text = new JTextField(8);
          area = new JTextArea(6,25);
          choice.addItem("音乐天地");
          choice.addItem("武术天地");
          choice.addItem("象棋乐园");
          choice.addItem("交友聊天");
        add = new JButton("添加");
        del = new JButton("删除");
         add.addActionListener(this);
         text.addActionListener(this);
         del.addActionListener(this);
         choice.addActionListener(this);
         add(choice);
         add(del);
         add(text);
         add(add);
         add(new JScrollPane(area));  
          
      }
      
      public void actionPerformed(ActionEvent e){
          if(e.getSource() == add || e.getSource() == text){
              String name = text.getText();
              if(name.length() > 0){
                  choice.addItem(name);
                  choice.setSelectedItem(name);
                  area.append("\n列表添加："+name);
              }
          }
          else if(e.getSource() == del){
              area.append("\n列表删除：" + choice.getSelectedItem());
              choice.remove(choice.getSelectedIndex());
              
          }
      }
   
    public void itemStateChanged(ItemEvent e) {
         String name =choice.getSelectedItem().toString();
         int index = choice.getSelectedIndex();
         area.setText("\n"+index+":"+name);
        
    }
    
}