Double Buffer Avoid Flashing

Sample.java

private Image bgImage;

@Override
public void update(Graphics g) {
    if (bgImage == null) bgImage = this.createImage(WIDTH, HEIGHT);
    Graphics bg = bgImage.getGraphics();
    bg.setColor(Color.BLACK);
    bg.fillRect(0, 0, WIDTH, HEIGHT);
    this.paintComponent(bg);
}

@Override
protected void paintComponent(Graphics g) {
    // painting stuff
}