rubberlinespanel.java

Java 程序设计教程（第五版）EXAMPLESchap07源码

//********************************************************************
//  RubberLinesPanel.java       Author: Lewis/Loftus
//
//  Represents the primary drawing panel for the RubberLines program.
//********************************************************************

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

public class RubberLinesPanel extends JPanel
{
   private Point point1 = null, point2 = null;

   //-----------------------------------------------------------------
   //  Constructor: Sets up this panel to listen for mouse events.
   //-----------------------------------------------------------------
   public RubberLinesPanel()
   {
      LineListener listener = new LineListener();
      addMouseListener (listener);
      addMouseMotionListener (listener);

      setBackground (Color.black);
      setPreferredSize (new Dimension(400, 200));
   }

   //-----------------------------------------------------------------
   //  Draws the current line from the intial mouse-pressed point to
   //  the current position of the mouse.
   //-----------------------------------------------------------------
   public void paintComponent (Graphics page)
   {
      super.paintComponent (page);

      page.setColor (Color.yellow);
      if (point1 != null && point2 != null)
         page.drawLine (point1.x, point1.y, point2.x, point2.y);
   }

   //*****************************************************************
   //  Represents the listener for all mouse events.
   //*****************************************************************
   private class LineListener implements MouseListener,
                                         MouseMotionListener
   {
      //--------------------------------------------------------------
      //  Captures the initial position at which the mouse button is
      //  pressed.
      //--------------------------------------------------------------
      public void mousePressed (MouseEvent event)
      {
         point1 = event.getPoint();
      }

      //--------------------------------------------------------------
      //  Gets the current position of the mouse as it is dragged and
      //  redraws the line to create the rubberband effect.
      //--------------------------------------------------------------
      public void mouseDragged (MouseEvent event)
      {
         point2 = event.getPoint();
         repaint();
      }

      //--------------------------------------------------------------
      //  Provide empty definitions for unused event methods.
      //--------------------------------------------------------------
      public void mouseClicked (MouseEvent event) {}
      public void mouseReleased (MouseEvent event) {}
      public void mouseEntered (MouseEvent event) {}
      public void mouseExited (MouseEvent event) {}
      public void mouseMoved (MouseEvent event) {}
   }
}