Weird Graphics2D situation encountered!!! please try to see this

Question

hello all! i've been doing an application which will display a window and is supposedly to paint its background with the GradientPaint method. i tried putting the method in a thread because i'm planning to display a moving text using the drawString in the future.
i've encountered this wierd problem: there are times when the frame gets painted and there are times when it's not. it's more often that the frame isn't painted. and not all of the time when it is painted that the whole frame is filled with the GradientPaint.
whenever the frame isn't painted "&&&&&&&&&&&&" from System.out.println("&&&&&&&&&&&&"); doesn't show up.
here's my code:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.*;
import javax.swing.border.*;
import java.awt.geom.*;
public class Test implements ActionListener {
public static void main(String[] args) {
f = new TestFrame();
f.show();
f.addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent e) {
     FlowLayout fl = new FlowLayout(0,30,30);
jd.setBounds(400,250,300,200);
jd.setResizable(false);
jd.getContentPane().setLayout(new FlowLayout(0,30,30));
l.setFont(new Font("Serif", Font.PLAIN, 18));
l.setLocation(0,0);
l.setFocusable(false);
jd.getContentPane().add(l);
     yes.setPreferredSize(new Dimension(100,50));
yes.setBorder(BorderFactory.createBevelBorder(BevelBorder.RAISED));
yes.setFont(new Font("Serif", Font.PLAIN, 18));
yes.addKeyListener(new KeyHandler());
yes.addActionListener(mp);
InputMap map = yes.getInputMap();
if (map != null){
map.put(KeyStroke.getKeyStroke(KeyEvent.VK_ENTER,0,false), "pressed");
map.put(KeyStroke.getKeyStroke(KeyEvent.VK_ENTER,0,true), "released");
jd.getContentPane().add(yes);
no.setPreferredSize(new Dimension(100,50));
no.setBorder(BorderFactory.createBevelBorder(BevelBorder.RAISED));
no.setFont(new Font("Serif", Font.PLAIN, 18));
no.addKeyListener(new KeyHandler());
no.addActionListener(mp);
InputMap map1 = no.getInputMap();
if (map1 != null){
map1.put(KeyStroke.getKeyStroke(KeyEvent.VK_ENTER,0,false), "pressed");
map1.put(KeyStroke.getKeyStroke(KeyEvent.VK_ENTER,0,true), "released");
jd.getContentPane().add(no);
     jd.show();
public void actionPerformed(ActionEvent e) {
String bname = e.getActionCommand();
if(bname=="Yes") {
System.exit(0);
jd.dispose();
static class KeyHandler extends KeyAdapter {
public void keyReleased(KeyEvent e) {     
int keycode = e.getKeyCode();
if(keycode==10 && yes.hasFocus()==true) {
System.exit(0);
static JFrame f;
static Test t = new Test();
static JDialog jd = new JDialog(f,"TEST");
static JLabel l = new JLabel("Would you like to close TEST?");
static JButton yes = new JButton("Yes");
static JButton no = new JButton("No");
class TestFrame extends JFrame {
public TestFrame() {
setBounds(wndSize.width/4,wndSize.height/4,wndSize.width/2,wndSize.height/2);
setDefaultCloseOperation(WindowConstants.DO_NOTHING_ON_CLOSE);
setResizable(false);
setTitle("test");
canvas = new JPanel();
getContentPane().add(canvas, "Center");
MoveThread mt = new MoveThread(canvas);
mt.start();
Toolkit theKit = getToolkit();
Dimension wndSize = theKit.getScreenSize();
Area area = new Area(new Rectangle2D.Double(0,0,510,345));
private JPanel canvas;
class MoveThread extends Thread {
public MoveThread(JPanel canvas) {
c = canvas;
public void paintComponent() {
Graphics2D g2 = (Graphics2D)c.getGraphics();
g2.setPaint(new GradientPaint(0,0,Color.green,510,345,Color.white));
System.out.println("&&&&&&&&&&&&");
g2.fill(area);
g2.dispose();
public void run() {
try {
paintComponent();
sleep(5);
} catch(Exception e) { }
private JPanel c = new JPanel();
Area area = new Area(new Rectangle2D.Double(0,0,510,345));
thanks for taking some time to look at this problem!
cheers, deo

Answer 1

Hi,
First, if you expect your paintComponent() method to get called by Swing then it should have a Graphics argument.
Second, it is normally a bad idea to get a Graphics from a component. You should use the one provided by the paintComponent() method.
Third, it is normally a bad idea to update anything in the GUI in a separate thread. Update your model but use the SwingUtilities.invokeLater() function to update your view of the data.
Forth, consider double buffering - draw your graphics onto an image and then use the paintComponent(Graphics g) to paint the image to the display.
Roger