complistenerdemo.java

来自「《java事件处理指南》一书的代码,好东西」· Java 代码 · 共 84 行

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

public class CompListenerDemo extends JFrame 
{
   private JLabel label;

   public CompListenerDemo()
   {

/*  A very long label is created and placed on a JFrame  */

      label = new JLabel("This is a very, very long label");
      label.setFont(new Font("Serif", Font.BOLD, 14));
      label.setForeground(Color.black);

      JPanel panel = new JPanel();
      panel.add(label);
      getContentPane().add(panel);

/*  The JFrame registers a ComponentListener    */

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

/*  The ComponentListener is implemented as an inner class.  When     */
/*  the JFrame is resized, a ComponentEvent is generated and sent     */
/*  to the componentResized() method.  This method tests to see       */
/*  if the JFrame width is smaller than the JLabel width.  If it      */
/*  is, the JFrame is resized so it is wider than the JLabel.         */
/*  If the JFrame is moved, a ComponentEvent is sent to the           */
/*  componentMoved() method.  The method determines if the frame      */
/*  has been moved off of the screen. If it has, the method moves     */
/*  the frame back on to the screen. The componentHidden() and        */
/*  componentShown() methods are not used, so they are implemented    */
/*  as stub methods.                                                  */

   class CompListener implements ComponentListener
   {
      public void componentResized(ComponentEvent event)
      {
         Component comp = event.getComponent(); 
         if ( comp.getWidth() < label.getWidth() )
         {
            comp.setSize( label.getWidth()+100, comp.getHeight() );
         }       
      }
      public void componentMoved(ComponentEvent event)
      {
         Dimension screenSize = 
                 Toolkit.getDefaultToolkit().getScreenSize();

         Component comp = event.getComponent(); 
         if ( comp.getX() < 0 )
         {
            setLocation(10, comp.getY()+30);
         }
         if ( comp.getX() > screenSize.width - getWidth() )
         {
            setLocation(screenSize.width-getWidth()-30, comp.getY()+30);
         }
         if ( comp.getY() < 0 )
         {
            setLocation(comp.getX(), 30);
         }
         if ( comp.getY() > screenSize.height - getHeight() )
         {
            setLocation(comp.getX(), screenSize.height-getHeight()-30);
         }
      }
      public void componentHidden(ComponentEvent event){}
      public void componentShown(ComponentEvent event){}
   }

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