JInternalFrame drawing problem.

Question

Hi gurus
Please could you help with a java problem that I cant find an answer to over the net:
I have a JDesktop which contains multiple JInternalFrames. On one JInternalFrame i have attached a JPanel on which to draw on. I have multiple threads (simple ball shapes) that need to be drawn onto the JPanel and have left it up to the indivual threads to draw themselves (as opposed to using paintComponent in the JPanel class). The drawing on the JInternalFrame works perfectly fine.
The problem arises when the other JInternalFrames are placed on top of each other - the balls are drawn over the top most JInternalFrame. What am i doing wrong? I have attached snippets of the code:
public class Desktop extends JFrame implements ActionListener
          public Desktop()
                    setTitle("Agent's world");
                    setSize(w,h);
                    setDefaultCloseOperation(EXIT_ON_CLOSE);
                    JDesktopPane desktop = new JDesktopPane();
                    setContentPane(desktop);
                    /************* Agent *************/
                    JInternalFrame agents = new JInternalFrame("Agents War", true, false, true, false);                    
                    agents.reshape(0,0,(int)((w/3)*2),h);
                    Container contentPane = agents.getContentPane();
                    canvas = new AgentPanel(agents);
                    contentPane.add(canvas);
                    /************* Button *************/
                    JPanel buttonPanel = new JPanel();
                    ButtonGroup buttonGroup = new ButtonGroup();
                    JButton start = new JButton("START");
                    start.addActionListener(this);
                    buttonPanel.add(start);
                    contentPane.add(buttonPanel, "North");
                    agents.setVisible(true);
                    desktop.add(agents);
                    //sets focus to other frames within the desktop
                    try
                              agents.setSelected(true);
                    catch(PropertyVetoException e)
                              //attempt to refocus was vetoed by a frame
          /** Method to listen for event actions, i.e. button clicks **/
     public void actionPerformed(ActionEvent event)
               //passes through 'this' to allow access to the getList method
               Agents agent = new Agents(canvas, this);
               agent.start();
public class Agents extends Thread
          public Agents(AgentPanel panel, Desktop desktop)
                    panel =_panel;
                    desktop = _desktop;
                    setDaemon(true);
/** Moves the agent from a spefic position to a new position **/
          public void move()
                    Graphics g = panel.getGraphics();
                    Graphics2D g2 = (Graphics2D)g;
                    try
                              //set XOR mode
                              g.setXORMode(panel.getBackground());
                              //draw over old
                              Ellipse2D.Double ballOld = new Ellipse2D.Double(i , j, length, length);
                              g2.fill(ballOld);     
                              i++;
                              j++;
                              if(flag == true)
                                        //draw new
                                        Ellipse2D.Double ballNew = new Ellipse2D.Double(i , j, length, length);
                                        g2.fill(ballNew);
                                        g2.setPaintMode();
                    finally
                              g.dispose();
          /** Activates the Thread **/
          public void run()
               int i = 0;
               while(!interrupted() && i<100)
                    try
                                   for(i = 0 ; i <100 ; i++)
                                             //draw ball in old position                                             move();          
                                             sleep(100);                              
                         catch(InterruptedException e)
public class AgentPanel extends JPanel
          /** local copy of internal frame */
          private JInternalFrame frame;
          public AgentPanel(JInternalFrame _frame)
                    frame = _frame;
                    setSize(frame.getWidth(), frame.getHeight());
                    setBackground(Color.white);          
          public void paintComponent(Graphics g)
                    super.paintComponent(g);
Thank you in advance.
Ravs

Answer 1

I have the same problem. Seems to be a bug. See:
http://forum.java.sun.com/thread.jsp?forum=57&thread=231037
Bummer.