下拉菜單不能選中

/* (swing1.1) */
//package jp.gr.java_conf.tame.swing.examples;

import java.util.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.*;

import jp.gr.java_conf.tame.swing.attribute.*;


/**
 * @version 1.0 12/26/98
 */  
public class DisabledComboBoxExample extends JFrame {

  public DisabledComboBoxExample() {
    super("Disabled Item ComboBox Example");  
    
    Object[] items = {
      new ComboItem("A")      ,new ComboItem("B"),
      new ComboItem("1",false),new ComboItem("2",false),
      new ComboItem("abc")    ,new ComboItem("def")
    };
                      
    JComboBox combo = new JComboBox(items);
    combo.setRenderer(new ComboRenderer());
    combo.addActionListener(new ComboListener(combo));
    
    getContentPane().setLayout(new FlowLayout());
    getContentPane().add(combo);
    setSize(300, 100);
    setVisible(true);
  }

  public static void main (String args[]) {
    DisabledComboBoxExample frame = new DisabledComboBoxExample();
    frame.addWindowListener(new WindowAdapter() {
      public void windowClosing(WindowEvent e) {
	System.exit(0);
      }
    });
  }
  
    
  class ComboRenderer extends JLabel implements ListCellRenderer {

    public ComboRenderer() {
      setOpaque(true);
      setBorder(new EmptyBorder(1, 1, 1, 1));
    }

    public Component getListCellRendererComponent( JList list, 
           Object value, int index, boolean isSelected, boolean cellHasFocus) {
      if (isSelected) {
        setBackground(list.getSelectionBackground());
        setForeground(list.getSelectionForeground());
      } else {
        setBackground(list.getBackground());
        setForeground(list.getForeground());
      }	
      if (! ((CanEnable)value).isEnabled()) {
        setBackground(list.getBackground());
        setForeground(UIManager.getColor("Label.disabledForeground"));
      }
      setFont(list.getFont());
      setText((value == null) ? "" : value.toString());
      return this;
    }  
  }
  
  class ComboListener implements ActionListener {
    JComboBox combo;
    Object currentItem;
    
    ComboListener(JComboBox combo) {
      this.combo  = combo;
      combo.setSelectedIndex(0);
      currentItem = combo.getSelectedItem();
    }
    
    public void actionPerformed(ActionEvent e) {
      Object tempItem = combo.getSelectedItem();
      if (! ((CanEnable)tempItem).isEnabled()) {
        combo.setSelectedItem(currentItem);
      } else {
        currentItem = tempItem;
      }
    }
  }
  
  class ComboItem implements CanEnable {
    Object  obj;
    boolean isEnable;
    
    ComboItem(Object obj,boolean isEnable) {
      this.obj      = obj;
      this.isEnable = isEnable;
    }
    
    ComboItem(Object obj) {
      this(obj, true);
    }
    
    public boolean isEnabled() {
      return isEnable;
    }
    
    public void setEnabled(boolean isEnable) {
      this.isEnable = isEnable;
    }
    
    public String toString() {
      return obj.toString();
    }
  }
}
======================================================

/*
 * (swing1.1)
 * 
 */

package jp.gr.java_conf.tame.swing.attribute;


/**
 * @version 1.0 12/26/98
 */

public interface CanEnable {
  
  public void setEnabled(boolean isEnable);
  public boolean isEnabled();

}