How to implement JPane that is animating

Well I admit - its a homework ;-).
I have to animate sth on a JPane, but I don't know how.
My current implementation is: to check in paint method whether some
defined time interval has passed, if so switch to next "Frame", and in
separate thread object repaint this pane often.

But if this thread has big priority GUI is not responsive, if low it
gets CPU time very rarely every so 3-4 seconds! While I need intervals
of 100ms.

Is there a better way of doing it?
Or there is flaw in my implementation. Thanks a lot in advance.

My implementation goes:

    private interface Paintable{
        Graphics paint(Graphics G);
    }

    private interface Animable extends Paintable{
        void increment();
        boolean hasFinished();
        int interval(); // returns about 100
        void reset();
    }

    private Vector Animables = new Vector();

       //paint method

                Iterator i = Animables.iterator(); //I may animate
more than one object at a time.
        Date temp = new Date();
        long interval = temp.getTime() - lastRepaint.getTime();
        lastRepaint = temp;
        boolean allFished=true;
        while(i.hasNext()){
            Animable p = (Animable) i.next();
            if(interval > p.interval()) p.increment();
            if(!p.hasFinished()) allFished=false;
            g = p.paint(g);
        }

// That thread

public class Waker extends Thread{
    private rysuje r;
    private boolean die=false;
    public Waker(rysuje r) {
        super();
        this.setPriority(5);
        this.r = r;
    }

    public void run(){
        while(!die){
            r.repaint();
            yield();
        }
    }

    public void setDie(boolean die) {
        this.die = die;

    }

}