Custom paint() and rare repainting

Question

I have made custom paint() method like this:
@Override
          public void paint(Graphics  g){
               int time;               
               if(renderer != null)
                    renderer.updateImage();
               time = Simulation.getCurrentStepTime();          
               if(time>=0)          labelCurrentTimeVal.setText(""+time);
               else              labelCurrentTimeVal.setText("-");
               time = Simulation.getAverageStepTime();          
               if(time>=0)          labelAvgTimeVal.setText(""+time);
               else              labelAvgTimeVal.setText("-");
               super.paint(g);
          }     I have some calculations going on in the background (separate thread). 'renderer' is responsible for repainting the JLabel holding an ImageIcon (which gets changed by the calculations). The case is that my background calculations take a few seconds. After they're done I call the repaint() method, which updates the image and paints the whole thing.
My problem is that I want to have up-to-date info on how much the iteration is taking so I`ve made the labelCurrentTimeVal JLabel to display it. The label only repaints when I call the repaint() method. However when I keep moving some slider in this panel repaint gets called all the time (I can see the labelCurrentTimeVal value changing constantly as I move the knob).
So what should I do to make the repaint() method get called often enough (20-30 times /sec to get about 20-30 fps)? I tried creating a different thread that calls repaint all the time (just to test it) and it doesn't solve the case.new Runnable() {
            public void run() {
                 while(true)
                      if(MainWindow.instance != null)
                           MainWindow.instance.repaint();
          };

Answer 1

I`ve made same code to represent the problem. The calculationThread does the calculations - in this case sets the iteration counter and the repaintThread is supposed to update the GUI and repaint it once in a while. GUI doesn't update at all and I don't get why?
import java.awt.Dimension;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
public class Main extends JFrame{     
     private JPanel panel;
     private JLabel label;
     public static Main window;
     private Runnable calcThread,repaintThread;
     private static int it;
     public static void main(String[] args) {
          new Main();
     private void createComponents(){
          window = this;
          panel = new JPanel();
          label = new JLabel("iteration:");
          panel.setPreferredSize(new Dimension(200,200));
          panel.add(label);
          this.add(panel);
          this.pack();
          this.setVisible(true);
     public Main(){
          createComponents();
          calcThread = new Runnable(){
               public void run(){
                    int i=0;                    
                    while(true){                         
                         Main.it = i;
                         System.out.println("check - iteration: "+i);
                         i++;
          repaintThread = new Runnable(){
               public void run(){
                    while(true){
                         try{
                              wait(30);
                              label.setText("iteration: "+it);     
                              window.repaint();
                         }catch(InterruptedException e){}
          calcThread.run();
          repaintThread.run();
}