Why drawImage(...) an off-screen image cause flicking

Question

Hi,
I tried to develop simple animation effects with the bufferred images but I found noticeable flicking. The codes I posted below were the modified version of the example code in the book Java2D.
Can someone help me out? I don't understand why flicking occurs.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public abstract class ApplicationFrame extends Frame implements ActionListener {
  protected Graphics2D offscreenGraphics2D = null;
  Timer drawtimer = new Timer(35, this);
  float alphavalue = (float)0.0;
  public ApplicationFrame() { this("ApplicationFrame v1.0"); }
  public ApplicationFrame(String title) {
    super(title);
    createUI();
  protected void createUI() {
    setSize(500, 400);
    center();
    addWindowListener(new WindowAdapter() {
      public void windowClosing(WindowEvent e) {
        dispose();
        System.exit(0);
  public void center() {
    Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
    Dimension frameSize = getSize();
    int x = (screenSize.width - frameSize.width) / 2;
    int y = (screenSize.height - frameSize.height) / 2;
    setLocation(x, y);
    drawtimer.start();
import java.awt.*;
import java.awt.geom.*;
import java.awt.event.*;
import javax.swing.*;
public class TransparentText {
  public static void main(String[] args) {
    ApplicationFrame f = new ApplicationFrame("TransparentText v1.0") {
      private int mNumberOfLines = 25;
      private Color[] mColors = { Color.red, Color.green, Color.blue };
      protected Image offscreenImage = null;
      public void actionPerformed(ActionEvent e) {
        alphavalue = alphavalue + (float)0.0033;
        if (alphavalue >= (float)0.9) {
           drawtimer.stop();
           return;
        repaint();       
      public void paint(Graphics g) {
//        System.out.println("paint() w/ alpha "+alphavalue);
        Graphics2D g2 = (Graphics2D)g;
        if (offscreenGraphics2D == null) {
           offscreenImage = createImage(500, 400);
           offscreenGraphics2D = (Graphics2D)offscreenImage.getGraphics();
        // Set the rendering quality.
        offscreenGraphics2D.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
               RenderingHints.VALUE_ANTIALIAS_ON); // this will affect the display of Chinese characters
        // Paint a red rectangle.
        Rectangle2D r = new Rectangle2D.Double(50, 50, 150, 100);
        offscreenGraphics2D.setPaint(Color.red);
        offscreenGraphics2D.fill(r);
        // Set a composite with transparency.
        Composite currentcomposite = offscreenGraphics2D.getComposite();
        Composite c = AlphaComposite.getInstance(AlphaComposite.SRC_OVER, alphavalue);
        offscreenGraphics2D.setComposite(c);
        // Draw some blue text.
        offscreenGraphics2D.setPaint(Color.blue);
        offscreenGraphics2D.setFont(new Font("Times New Roman", Font.PLAIN, 72));
        offscreenGraphics2D.drawString("Composite", 25, 130);
        offscreenGraphics2D.setComposite(currentcomposite); // restore it
        g2.drawImage(offscreenImage, 0, 0, this);
    f.setSize(400, 200);
    f.center();
    f.setVisible(true);
}

Answer 1

It's because the update() method first paints the component in its background colour, then calls paint(). Override it to just call paint(), ie
public void update(Graphics g)
    paint(g);
}And using the paint method directly in an anonymous frame is a pretty unpleasant way to do it - better to create a subclass of JPanel, override the paint method in there and use it in the JFrame (either set it as the content pane or add it to it).