mouseeventdemo.java

《java事件处理指南》一书的代码,好东西

import java.awt.*;
import java.awt.event.*;

public class MouseEventDemo extends Frame 
{
   private Canvas canvas; 
   private int startX, startY, endX, endY;

   public MouseEventDemo()
   {

/*  A Canvas object is placed on a Frame and registers a   */
/*  MouseListener and a MouseMotionListener.               */

      canvas = new Canvas();
      canvas.addMouseListener(new MouseHandler());
      canvas.addMouseMotionListener(new MouseMotionHandler());

      add(canvas);

      addWindowListener(new WinAdapter());
      setBounds(100, 100, 300, 200);
      setVisible(true);
   }

/*  Both the MouseListener and the MouseMotionListener are implemented  */
/*  as extensions of the corresponding adapter class.  The purpose of   */
/*  the listeners is to draw a line on the Canvas when the mouse is     */
/*  dragged.  When the mouse is pressed, this indicates the starting    */
/*  point of the line.  A MouseEvent is generated and sent to the       */
/*  mousePressed() method.  The event is used to get the current        */
/*  position of the mouse and set the starting point of the line.       */

   class MouseHandler extends MouseAdapter
   {
      public void mousePressed(MouseEvent event)
      {
         startX = event.getX();
         startY = event.getY();
         endX = startX;
         endY = startY;
      }
   }

/*  When the mouse is dragged acrosss the Canvas, MouseEvents are     */
/*  generated and set to the mouseDragged() method.  A line is drawn  */
/*  on the Canvas that tracks the motion of the mouse.                */

   class MouseMotionHandler extends MouseMotionAdapter
   {
      public void mouseDragged(MouseEvent event)
      {
         startX = endX;
         startY = endY;
         endX = event.getX();
         endY = event.getY();
         canvas.getGraphics().drawLine(startX, startY, endX, endY);
      }
   }

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

/*  This makes sure the application terminates if the window is closed   */

class WinAdapter extends WindowAdapter
{
   public void windowClosing(WindowEvent event) 
   {
      System.exit(0);
   }
}