Fine Tuning Java 1.1 Double Buffering?

Question

Dear Java gurus,
Hi, I'm looking for suggestions on improving the performance of my double buffering technique for pure Java 1.1 applets.
My current method seems to eat up more CPU & RAM than it should. I fear that real implementations (with far more drawing to the buffer before update), would be impractically slow and choke using double buffering the way I am now.
I have programmed a simple applet demonstrating my current method (code below), which runs at 20 fps. I tried to keep it short and sweet.
I'm only looking for pure Java 1.1 code.
Thanks in advance. =)
import java.awt.*;
import java.applet.*;
public class ColourFader extends Applet implements Runnable {
// Class Variables
     int appletWidth = 600;
     int appletHeight = 300;
     int fps = 20;
     int delay = 1000 / fps;
     int nextRGB [] = {255, 0, 255};
     int currRGB [] = {0, 255, 0};
// Class Objects
     Image offImage;
     Graphics offGraphics;
     Thread animator;
// Applet Methods          
     public void start() {
          animator = new Thread(this);
          animator.start();
          offImage = createImage(appletWidth, appletHeight);
          offGraphics = offImage.getGraphics();
     public void stop() {
          animator = null;
          offImage = null;
          offGraphics = null;
     public void paint(Graphics g) {
          g.drawImage(offImage, 0, 0, null);
          update(g);
// Runnable Method
     public void run() {
          while(Thread.currentThread() == animator) {
               long tm = System.currentTimeMillis();
               repaint();
               try {
                    tm += delay;
                    Thread.sleep(Math.max(0, tm - System.currentTimeMillis()));
               } catch (InterruptedException e) {
                    break;
// Convenience Methods
     public void update(Graphics g) {
          fadeRGBValues();
          paintFrame(offGraphics);
          g.drawImage(offImage, 0, 0, null);
     public void paintFrame(Graphics g) {
          g.setColor(new Color(currRGB[0], currRGB[1], currRGB[2]));
          g.fillRect(0, 0, appletWidth, appletHeight);          
     public void fadeRGBValues() {
          for(int i = 0; i <= 2; i++) {
               if(currRGB[i] < nextRGB) {
                    currRGB[i] += 1;
               } else if (currRGB[i] > nextRGB[i]) {
                    currRGB[i] -= 1;
               } else {
                    nextRGB[i] = randomNum();
     public int randomNum() {
          double randomDouble = Math.random() * 255.0;
          int randomInt = (int) randomDouble;
          return(randomInt);

Answer 1

Usually first update is called, then paint. In your paint method you call update, I don't see any reason for that. You want your paint method to be fast, so I would remove the update call.
Instead I would call paint from the update method. Update is not needed to be called as often as the paint method. I think I would make the update method do nothing (just call the paint method). Then I would make another method I could call when I need to make some updates, and which did not take any graphics object as argument, becuase you dont need it.
So something like this:
public void update(Graphics g) {
  paint(g);
public void paint(Graphics g) {
  g.drawImage(offImage, 0, 0, null);
public void update() {
  fadeRGBValues();
  paintFrame(offGraphics); 
}Then in your run method, just before repaint(), I would call update().
Thread.sleep(0) would sleep forever I think. So be careful with that. A better way to do it:
public void run() {
  long start = System.currentTimeMillis();
  int count = 0;
  while (Thread.currentThread() == animator) {
    update();
    repaint();
    count++;
    long sleep = count*delay-(System.currentTimeMillis()-start);
    if (sleep > 0) {
      try {
        Thread.sleep(sleep);
      } catch (InterruptedException e) {
        break;
}