focusadapterdemo.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 FocusAdapterDemo extends JFrame
{
   private JTextField jtf1, jtf2, jtf3;
   private JLabel label1, label2;

   public FocusAdapterDemo()
   {
/*   Two JLabels and three JTextFields are created.   */
/*   Two of the textfields register a FocusListener   */

      jtf1 = new JTextField(20); 
      jtf1.setBorder(BorderFactory.createLineBorder(Color.black));
      jtf1.setName("TextField 1");
      jtf1.addFocusListener(new FocusHandler());

      jtf2 = new JTextField(20); 
      jtf2.setBorder(BorderFactory.createLineBorder(Color.black));
      jtf2.setName("TextField 2");
      jtf2.addFocusListener(new FocusHandler());

      jtf3 = new JTextField(20);
      jtf3.setEditable(false);

      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 */

      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, BorderLayout.CENTER);
      getContentPane().add(jtf3, BorderLayout.SOUTH);

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

/*  The FocusListener is implemented as an inner class that extends    */
/*  the FocusAdapter class.  Whenever one of the JTextField objects    */
/*  gains keyboard focus, a FocusEvent is generated and sent to the    */
/*  focusGained() method.  The JTextField  at the bottom of the        */
/*  JFrame is used to indicate which component has focus.              */

   class FocusHandler extends FocusAdapter
   {
      public void focusGained(FocusEvent event)
      {
         JTextField tf = (JTextField)event.getComponent();
         jtf3.setText(tf.getName()+" has focus");
      }

   }

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