starfield1.java

java 完全探索的随书源码

// StarField1.java

import java.awt.*;
import java.applet.Applet;

public class StarField1 extends Applet implements Runnable
{
   Thread t;
   int counter;

   Color starColors [] = { Color.white, Color.darkGray, Color.lightGray,
                           Color.blue, Color.yellow };

   public void start ()
   {
      if (t == null)
      {
          t = new Thread (this);
          counter = 0;
          t.start ();
      }
   }

   public void stop ()
   {
      t = null;
   }

   public void run ()
   {
      Thread current = Thread.currentThread ();

      while (t == current)
      {
         // Draw frame

         repaint (); // This method causes the update method to be called.

         // Pause

         try
         {
            Thread.sleep (50);
         }
         catch (InterruptedException e) {}
         
         // Manipulate counter

         if (++counter > 500)
             counter = 0;
      }
   }

   public void paint (Graphics g)
   {
      // The following getClipBounds method call returns
      // a rectangle that contains the dimensions of the
      // clip (a rectangular portion of the drawing
      // surface that must be redrawn, because of
      // damage).  Damage represents a "hole" in the
      // drawing surface.  It occurs when a window
      // partially (or completely) obscures the drawing
      // surface and then is removed.  Because the
      // surface's obscured pixels were replaced by the
      // overlapping window, they must be redrawn.
      // Rather than redraw the entire drawing surface,
      // only the clip should be redrawn -- which also
      // improves drawing performance.

      Rectangle r = g.getClipBounds ();

      // Redraw the clip area by filling all pixels with
      // the color black.  Any stars in this area will be
      // wiped out.

      g.setColor (Color.black);
      g.fillRect (r.x, r.y, r.width, r.height);
   }

   // Return a random integer from 0 through limit - 1.

   int rnd (int limit)
   {
      return (int) (Math.random () * limit);
   }

   public void update (Graphics g)
   {
      // When there are enough stars, redraw the background
      // and erase visible stars.

      if (counter == 0)
          paint (g);

      // Set the next star's color and draw this star.

      g.setColor (starColors [rnd (starColors.length)]);

      int x = rnd (getSize ().width);
      int y = rnd (getSize ().height);

      g.drawLine (x, y, x, y);
   }
}