Double buffering still gives flickering graphics.

Question

I copied code from a tutorail which is supposed to illustrate double buffering.
After I run it, it still flickers though.
I use applet viewer, which is part of netbeans to run my applet.
Link to tutorial: http://www.javacooperation.gmxhome.de/TutorialStartEng.html
My questions are:
Is the strategy used for double buffering correct?
Why does it flicker?
Why does the program change the priority a couple of times?
Can you make fast games in JApplets or is there a better way to make games? (I think C++ is too hard)
Here is the code:
package ballspel;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Image;
import javax.swing.JApplet;
//import java.applet.*;
* @author Somelauw
public class BallApplet extends /*Applet*/ JApplet implements Runnable {
private Image dbImage;
private Graphics dbg;
private int radius = 20;
private int xPos = 10;
private int yPos = 100;
* Initialization method that will be called after the applet is loaded
* into the browser.
@Override
public void init() {
//System.out.println(this.isDoubleBuffered()); //returns false
// Isn't there a builtin way to force double buffering?
// TODO start asynchronous download of heavy resources
@Override
public void start() {
Thread th = new Thread(this);
th.start();
public void run() {
Thread.currentThread().setPriority(Thread.MIN_PRIORITY);
while (true) {
xPos++;
repaint();
try {
Thread.sleep(20);
} catch (InterruptedException ex) {
ex.printStackTrace();
Thread.currentThread().setPriority(Thread.MAX_PRIORITY);
@Override
public void paint(Graphics g) {
super.paint(g);
//g.clear();//, yPos, WIDTH, WIDTH)
g.setColor(Color.red);
g.fillOval(xPos - radius, yPos - radius, 2 * radius, 2 * radius);
@Override
public void update(Graphics g) {
super.update(g);
// initialize buffer
if (dbImage == null) {
dbImage = createImage(this.getSize().width, this.getSize().height);
dbg = dbImage.getGraphics();
// clear screen in background
dbg.setColor(getBackground());
dbg.fillRect(0, 0, this.getSize().width, this.getSize().height);
// draw elements in background
dbg.setColor(getForeground());
paint(dbg);
// draw image on the screen
g.drawImage(dbImage, 0, 0, this);
// TODO overwrite start(), stop() and destroy() methods
}

Answer 1

Somelauw wrote:
I copied code from a tutorail which is supposed to illustrate double buffering.
After I run it, it still flickers though.
I use applet viewer, which is part of netbeans.. AppletViewer is part of the JDK, not NetBeans.
..to run my applet.
Link to tutorial: http://www.javacooperation.gmxhome.de/TutorialStartEng.html
Did you specifically mean the code mentioned on this page?
[http://www.javacooperation.gmxhome.de/BildschirmflackernEng.html]
Don't expect people to go hunting around the site, looking for the code you happen to be referring to.
As an aside, please use the code tags when posting code, code snippets, XML/HTML or input/output. The code tags help retain the formatting and indentation of the sample. To use the code tags, select the sample and click the CODE button.
Here is the code you posted, as it appears in code tags.
package ballspel;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Image;
import javax.swing.JApplet;
//import java.applet.*;
* @author Somelauw
public class BallApplet extends /*Applet*/ JApplet implements Runnable {
    private Image dbImage;
    private Graphics dbg;
    private int radius = 20;
    private int xPos = 10;
    private int yPos = 100;
     * Initialization method that will be called after the applet is loaded
     * into the browser.
    @Override
    public void init() {
        //System.out.println(this.isDoubleBuffered()); //returns false
        // Isn't there a builtin way to force double buffering?
        // TODO start asynchronous download of heavy resources
    @Override
    public void start() {
        Thread th = new Thread(this);
        th.start();
    public void run() {
        Thread.currentThread().setPriority(Thread.MIN_PRIORITY);
        while (true) {
            xPos++;
            repaint();
            try {
                Thread.sleep(20);
            } catch (InterruptedException ex) {
                ex.printStackTrace();
            Thread.currentThread().setPriority(Thread.MAX_PRIORITY);
    @Override
    public void paint(Graphics g) {
        super.paint(g);
        //g.clear();//, yPos, WIDTH, WIDTH)
        g.setColor(Color.red);
        g.fillOval(xPos - radius, yPos - radius, 2 * radius, 2 * radius);
    @Override
    public void update(Graphics g) {
        super.update(g);
        // initialize buffer
        if (dbImage == null) {
            dbImage = createImage(this.getSize().width, this.getSize().height);
            dbg = dbImage.getGraphics();
        // clear screen in background
        dbg.setColor(getBackground());
        dbg.fillRect(0, 0, this.getSize().width, this.getSize().height);
        // draw elements in background
        dbg.setColor(getForeground());
        paint(dbg);
        // draw image on the screen
        g.drawImage(dbImage, 0, 0, this);
    // TODO overwrite start(), stop() and destroy() methods
}Edit 1:
- For animation code, it would be typical to use a javax.swing.Timer for triggering updates, rather than implementing Runnable (etc.)
- Attempting to set the thread priority will throw a SecurityException, though oddly it occurs when attempting to set the Thread priority to maximum, whereas the earlier call to set the Thread priority to minimum passed without comment (exception).
- The paint() method of that applet is not double buffered.
- It is generally advisable to override paintComponent(Graphics) in a JPanel that is added to the top-level applet (or JFrame, or JWindow, or JDialog..) rather than the paint(Graphics) method of the top-level container itself.
Edited by: AndrewThompson64 on Jan 22, 2010 12:47 PM