Making GUI update at correct time

Question

I'm creating an engine that can display experimental stimuli for my lab working with kids with reading disabilities. I have a GUI which can display the next stimuli in the test. Once the stimuli are displayed, the program does nothing until the user presses a button and a key event is called.
I'm now trying to get my GUI to play recorded words to the user. Because it's the responsibility of the GUI to display stimuli, the GUI will be the one playing the sound (even though that's not typically thought of as a GUI responsibility). Unfortunately, even though the commands to update the GUI display are placed before the command to play the sound, the GUI does not update until it has finished playing the sound.
This has nothing to do with the sound itself: if I replace the clip.play() line with a loop that wastes time and spins around for five seconds, the GUI does not update for those five seconds.
The GUI updates itself the moment the program leaves the setStimuli() method. How can I get it to update itself before then? Commands such as this.repaint() don't appear to work.
Any thoughts on how to get the GUI to update itself before exiting the method?
public class TestingEngine {
public void setStimuli(String[] values) {
   gui.setStimuli(values);
public class GUI extends javax.swing.JFrame {
public void setStimuli(String[] values){
       switch (testType){
         case SOUND:
               String soundImageFile = "Headphones.jpg";
               ImageIcon soundImage = new ImageIcon(soundImageFile);
               JLabel soundImageLabel = new JLabel(soundImage);
               SoundImageJPanel.removeAll();
               SoundImageJPanel.repaint();
               SoundImageJPanel.add(soundImageLabel);
               soundImageLabel.setVisible(true);
               label_S_Option1.setText(values[1]);
               label_S_Option2.setText(values[2]);           // <-- nothing has updated yet
               SoundClip clip = new SoundClip(values[0]);
               if (clip.isInitialized())                     // <-- this section could also be replaced
                   clip.play();                             // by a time-wasting loop
               break;
    }      // <-- once program reaches here, GUI finally updates
}

Answer 1

Ok, so just for the sake of it, I tried using the Timer method as suggested in the thread you pointed me to. This doesn't do anything, but thinking about it, I don't see why it would. Timer calls repaint() every 50 ms, but, after all, the setStimuli() method also called repaint() before playing the soundclip. If the original call of repaint() didn't do anything, then I don't think that calling it more often would.
Is there another command that I should be using? In other words, how can I tell my JFrame and JLabels to "UPDATE RIGHT NOW, NOT IN A MINUTE!"? (It would be easier if I were the JFrame's mother...)
Current version of code, with Timer class:
public class GUI extends javax.swing.JFrame {
   private Thread refresh;
   public GUI() {
       initComponents();
       refresh = new Timer(this);
       refresh.start();
   public void setStimuli(String[] values){
       switch (testType){
         case SOUND:
               String soundImageFile = "Headphones.jpg";
               ImageIcon soundImage = new ImageIcon(soundImageFile);
               JLabel soundImageLabel = new JLabel(soundImage);
               SoundImageJPanel.removeAll();
               SoundImageJPanel.repaint();
               SoundImageJPanel.add(soundImageLabel);
               soundImageLabel.setVisible(true);
               label_S_Option1.setText(values[1]);
               label_S_Option2.setText(values[2]);           // <-- nothing has updated yet
               SoundClip clip = new SoundClip(values[0]);
               if (clip.isInitialized())                     // <-- this section could also be replaced
                   clip.play();                              // by a time-wasting loop (same problem)
               break;
   }      // <-- once program reaches here, GUI finally updates
   public void callback(){
       repaint();
class Timer extends Thread
     private Gui parent;
     public Timer(Gui g) {
          parent = g;
     synchronized public void run() {
          while(true) {
               try{
                   wait(50);
               }catch(InterruptedException ie) {return;}
               parent.callBack();
}