itemeventdemo.java

《java事件处理指南》一书的代码,好东西

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

public class ItemEventDemo extends JFrame 
{
   private JComboBox jcb;
   private JTextField jtf;

   public ItemEventDemo()
   {
      jtf = new JTextField(20);
      jtf.setText("Selection is ");
      jtf.setEditable(false);

/*  A JComboBox is created and placed on a JFrame.  The JComboBox   */
/*  registers an ItemListener                                       */

      String[] food = {"hamburger", "pizza", "lentil soup"};
      jcb = new JComboBox(food);
      jcb.setBorder(BorderFactory.createLineBorder(Color.black));
      jcb.addItemListener(new ItemEventHandler());

      JPanel southPanel = new JPanel();
      southPanel.add(jtf);

      JPanel centerPanel = new JPanel();
      centerPanel.add(jcb);

      getContentPane().add(southPanel, BorderLayout.SOUTH);
      getContentPane().add(centerPanel, BorderLayout.CENTER);

      setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      setBounds(100, 100, 300, 200);
      setVisible(true);
   }

/*  The ItemListener is implemented as an inner class.  When the user  */
/*  makes a selection, an ItemEvent is generated and sent to the       */
/*  itemStateChanged() method.  This method updtates the JTextField    */
/*  to indicate the new selection.                                     */

   class ItemEventHandler implements ItemListener
   {
      public void itemStateChanged(ItemEvent event)
      {
         jtf.setText("Selection is "+event.getItem());
      }
   }

   public static void main(String args[])
   {
      ItemEventDemo demo = new ItemEventDemo();
   }
}