moveboxinnercanvas.java

Java程序设计技巧与开发实例附书源代码。

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

public class MoveBoxInnerCanvas
    extends JApplet
    implements ActionListener
{
   private final int BOX_WIDTH = 30;
   private final int BOX_HEIGHT = 20;
   private final int INC = 4;
   private final Color COLOR = Color.red;
   private JButton left = new JButton("Left");
   private JButton right = new JButton("Right");
   private JButton up = new JButton("Up");
   private JButton down = new JButton("Down");
   private int x = 50, y = 50;
   private class MoveBoxCanvas
       extends JPanel
   {
      public void paintComponent(Graphics g)
      {
         super.paintComponent(g);
         g.setColor(COLOR);
         g.fillRect(x, y, BOX_WIDTH, BOX_HEIGHT);
         g.setColor(Color.black);
         g.drawRect(0, 0, getSize().width - 1, getSize().height - 1);
      }
   }

   private MoveBoxCanvas drawing = new MoveBoxCanvas();

   public void init()
   {
      JPanel buttons = new JPanel(new FlowLayout());
      buttons.add(up);
      up.addActionListener(this);
      buttons.add(down);
      down.addActionListener(this);
      buttons.add(left);
      left.addActionListener(this);
      buttons.add(right);
      right.addActionListener(this);
      drawing.setBorder(new TitledBorder("The Box Playground"));
      buttons.setBorder(new TitledBorder("Move the Box"));
      try
      {
         URL base = getCodeBase();
         up.setIcon(new ImageIcon(new URL(base, "up.gif")));
         down.setIcon(new ImageIcon(new URL(base, "down.gif")));
         left.setIcon(new ImageIcon(new URL(base, "left.gif")));
         right.setIcon(new ImageIcon(new URL(base, "right.gif")));
      }
      catch (MalformedURLException murle)
      {
         System.err.println("Error");
      }
      up.setToolTipText("Box up");
      down.setToolTipText("Box down");
      right.setToolTipText("Box right");
      left.setToolTipText("Box left");
      getContentPane().setLayout(new BorderLayout());
      getContentPane().add("South", buttons);
      getContentPane().add("Center", drawing);
   }

   public void actionPerformed(ActionEvent e)
   {
      if (e.getSource() == up)
      {
         y -= INC;
      }
      else if (e.getSource() == down)
      {
         y += INC;
      }
      else if (e.getSource() == left)
      {
         x -= INC;
      }
      else if (e.getSource() == right)
      {
         x += INC;
      }
      drawing.repaint();
   }
}