focuseventdemo.java

《java事件处理指南》一书的代码,好东西

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

public class FocusEventDemo extends JFrame
{
   private JTextField jtf1, jtf2;
   private JLabel label1, label2;

   public FocusEventDemo()
   {
/*   Two JLabels and two JTextFields are created    */

      jtf1 = new JTextField(20); 
      jtf1.setBorder(BorderFactory.createLineBorder(Color.black));
      jtf1.setBackground(Color.lightGray);
      jtf1.addFocusListener(new FocusHandler());

      jtf2 = new JTextField(20); 
      jtf2.setBorder(BorderFactory.createLineBorder(Color.black));
      jtf2.setBackground(Color.lightGray);
      jtf2.addFocusListener(new FocusHandler());

      label1 = new JLabel("Line 1");
      label1.setForeground(Color.black);

      label2 = new JLabel("Line 2");
      label2.setForeground(Color.black);

/*  The components are placed on the JFrame using a BoxLayout   */

      JPanel p1 = new JPanel();
      p1.add(label1);
      p1.add(jtf1);

      JPanel p2 = new JPanel();
      p2.add(label2);
      p2.add(jtf2);

      JPanel panel = new JPanel();
      panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS));
      panel.add(p1);
      panel.add(p2);

      getContentPane().add(panel);

      setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      setBounds(100, 100, 400, 200);
      setVisible(true);
   }

/*  The FocusListener is implemented as an inner class.  Whenever     */
/*  one of the JTextField objects gains keyboard focus, a FocusEvent  */
/*  is generated and sent to the focusGained() method.                */
/*  The background color of the JTextField that generated the event   */
/*  is set to pink.  Similarly, if a JTextField loses keyboard        */
/*  focus the focusLost() method is called and the background color   */
/*  is set to light gray.                                             */

   class FocusHandler implements FocusListener
   {
      public void focusGained(FocusEvent event)
      {
         JTextField tf = (JTextField)event.getComponent();
         tf.setBackground(Color.pink);
      }

      public void focusLost(FocusEvent event)
      {
         JTextField tf = (JTextField)event.getComponent();
         tf.setBackground(Color.lightGray);
      }
   }

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