bullseyepanel.java

Java 程序设计教程（第五版）EXAMPLESchap05源码

//********************************************************************
//  BullseyePanel.java       Author: Lewis/Loftus
//  
//  Demonstrates the use of conditionals and loops to guide drawing.
//********************************************************************

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

public class BullseyePanel extends JPanel
{
   private final int MAX_WIDTH = 300, NUM_RINGS = 5, RING_WIDTH = 25;

   //-----------------------------------------------------------------
   //  Sets up the bullseye panel.
   //-----------------------------------------------------------------
   public BullseyePanel ()
   {
      setBackground (Color.cyan);
      setPreferredSize (new Dimension(300,300));
   }

   //-----------------------------------------------------------------
   //  Paints a bullseye target.
   //-----------------------------------------------------------------
   public void paintComponent (Graphics page)
   {
      super.paintComponent (page);

      int x = 0, y = 0, diameter = MAX_WIDTH;

      page.setColor (Color.white);

      for (int count = 0; count < NUM_RINGS; count++)
      {
         if (page.getColor() == Color.black)  // alternate colors
            page.setColor (Color.white);
         else
            page.setColor (Color.black);

         page.fillOval (x, y, diameter, diameter);

         diameter -= (2 * RING_WIDTH);
         x += RING_WIDTH;
         y += RING_WIDTH;
      }

      // Draw the red bullseye in the center
      page.setColor (Color.red);
      page.fillOval (x, y, diameter, diameter);
   }
}