ShapesApplet

import java.awt.*;
import java.lang.Math;
import java.util.Random;

/**
  A simple applet to illustrate multithreaded programming.
  It consists of shapes, each running in its own thread that
  ebb and flow at different rates.

  @Author: Suresh Srinivasan (suresh@thomtech.com)
  @Date: Oct 1995
  @Version: 0.1
 */

public class ShapesApplet extends java.applet.Applet {
    public int W = 400;
    public int H = 100;
    public int N = 15;
    public final int minSize = 10;
    public final int maxSize = 50;
    public final int minNaptime = 1;
    public final int maxNaptime = 500;
    public final Color colors[] = {
	Color.red,
	Color.pink,
	Color.orange,
	Color.yellow,
	Color.green,
	Color.magenta,
	Color.blue,
	Color.cyan,
	Color.white,
	Color.gray,
	Color.lightGray,
	Color.darkGray
    };
    public final Color bg = Color.black;
    boolean threadSuspended = false;
    Image im;
    Graphics offscreen;
    Random rand;
    Shape shapes[] = new Shape[N];

    public void init() {
	resize(W, H);
	rand = new Random((long)System.currentTimeMillis());
	try {
	    im = createImage(W, H);
	    offscreen = im.getGraphics();
	} catch (Exception e) {
	    offscreen = null;
	}
    }

/*
  Create each shape with some random parameters and start its thread
  */
    public void start() {
	for (int i=0; i<N; i++) {
	    if (shapes[i] == null) {
		shapes[i] = new Shape(this,
		    (int)((double)W*rand.nextDouble()),
		    (int)((double)H*rand.nextDouble()),
		    minSize + (int)((double)(maxSize-minSize)*rand.nextDouble()),
		    minNaptime + (int)((double)(maxNaptime-minNaptime)*rand.nextDouble()),
		    colors[(int)((double)colors.length*rand.nextDouble())],
		    bg);
		shapes[i].start();
	    }
	}
	repaint();
    }

/* when applet is stopped, stop individual threads */
    public void stop() {
	for (int i=0; i<N; i++) {
	    shapes[i].stop();
	}
    }

/* override the update method to reduce flashing */
    public void update(Graphics g) {
	paint(g);
    }

/* we are using double buffering to reduce flashing */
    public void paint(Graphics g) {
	if (offscreen != null) {
	    paintApplet(offscreen);
	    g.drawImage(im, 0, 0, this);
	} else {
	    paintApplet(g);
	}
    }

/* call each shape's paint method */
    public void paintApplet(Graphics g) {
	boolean changed = false;

	g.setColor(bg);
	g.fillRect(0, 0, W, H);
	for (int i=0; i<N; i++) {
	    shapes[i].paint(g);
	}
    }

/* on mouse activity, suspend (or resume) each shape's thread */
    public boolean mouseDown(Event e, int x, int y) {
	if (threadSuspended) {
	    for (int i=0; i<N; i++)
		shapes[i].thread.resume();
	} else {
	    for (int i=0; i<N; i++)
		shapes[i].thread.suspend();
	}
	threadSuspended = !threadSuspended;
	return(true);
    }

}

/**
  Implements a Shape.  Each shape will call its applet's paint method
  asynchronously when it is time for growth or decay.
  */
class Shape implements Runnable {
    static int threadNum = 1;
    private Color color = null;
    private Color bg = Color.black;
    private int naptime = 500;
    private int size = 50;
    private int growthFactor = 1;
    private int ox = 0;		/* location within applet's frame of reference */
    private int oy = 0;
    private Graphics graphics;
    private int current;
    private int previous;
    private boolean growing = false;

    public Thread thread = null;
    public boolean changed = true;

    ShapesApplet applet;

    public Shape(ShapesApplet applet, int x, int y, int s, int n, Color c, Color bg) {
	this.applet = applet;
	ox = x;
	oy = y;
	size = s;
	naptime = n;
	color = c;
	if (color == null) {
	    color = Color.black;
	}
	current = previous = s;
    }

/* the thread's run method */
    public void run() {
	thread.setPriority(Thread.MIN_PRIORITY+1);
	while (thread != null) {
	    changed = true;
	    previous = current;
	    if (growing) {
		current += growthFactor;
	    } else {
		current -= growthFactor;
	    }
	    if (current == size || current == 0) {
		growing = !growing;
	    }
	    try { thread.sleep(naptime); } catch (InterruptedException e) {};
	    applet.repaint();
	}
	thread = null;
    }

/* start the thread */
    public void start() {
	if (thread == null) {
	    thread = new Thread(this, Integer.toString(threadNum++));
	    thread.start();
	}
    }

    public void stop() {
	thread = null;
    }

/* unpaint last position and paint the new one */
    public void paint(Graphics g) {
	int prevHalf = (int)(previous/2);
	int curHalf = (int)(current/2);

	g.setColor(bg);
	g.fillRect(ox-prevHalf, oy-prevHalf, previous, previous);
//	g.fillOval(ox-prevHalf, oy-prevHalf, previous, previous);

	g.setColor(color);
	g.fillRect(ox-curHalf, oy-curHalf, current, current);
//	g.fillOval(ox-curHalf, oy-curHalf, current, current);
    }
}

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