Player's position slider (Thread not owner)

Question

Hi every1,
I've a thread that sets a slider value with the player's time in secods,but in case the slider Knob is dragged by the user the thread should wait and player's time should be set as per the value dragged by the user.
But the wait() method is not executing instead it generates IllegalMonitorStateException: current thread not owner exception. Would you help me please?
My code is:
//the thread which sets the slider value as the time in second increases
public void run() {
     while (true) {
                    if (player != null) {
           nano = player.getMediaTime().getSeconds();
          if (dura >nano) {
              timex = (int)nano;
                    jSlider.setValue(timex);
                 try {
          Thread.currentThread().sleep(1000);
         } catch (InterruptedException ie) {
    }//the method which sets the slider as a user moves the knob of the slider
jSlider.addChangeListener(new javax.swing.event.ChangeListener() {
            public void stateChanged(javax.swing.event.ChangeEvent evt) {
               try{
                  if(jSlider.getValueIsAdjusting()){
player.setMediaTime(new javax.media.Time((double)  
jSlider.getValue())); 
                thr.wait();                  }
               }catch(Exception e){e.printStackTrace();
                  System.out.println("Exception @ jSlider stateChanged : " + e.getMessage() );
        });Thanks!

Answer 1

The exception is happening because the ChangeListener thread does not own the monitor on "thr" (see the api documentation for Object.wait). That can be fixed by putting it in a synchronized (this) { ... } block.
However, I see bigger problems. First, recognize that Java is going to call your ChangeEvent code on the event handling thread, so you definitely don't want it to wait. The screen will stop repainting and the user's mouse release event won't be processed, because you will have suspended the thread that handles those things. Second, you should not modify the position of the slider from any thread other than the event handling thread, for reasons documented at [http://java.sun.com/developer/technicalArticles/Threads/swing/]. That article also shows techniques that are safe.
I don't mean to be discouraging, just wanted to point out a couple more things so you didn't get strange behavior without knowing why! What you are attempting actually requires some multi-threading skill, so study up!
Cheers,
Eric