Basic threading question

Question

I've tried to understand threading from ten different tutorials, but it makes my head spin because all the tutorials include so much extra stuff that I don't know what's important.
I've got a piece of code here with a gui, which contains a progress bar. I'd like the progress bar to update in a timely fashion, but not take up much of the main thread's recources.
I've cut the code down to it's barest minimum. I'd really appreciate it if someone could tell me how to edit this code so that it implements threading. Thanks so very much.
public class MeGA {
     private static Interface gui;
     private static EvolutionEngine engine;
     public static void main(String[] args) {
          engine = new EvolutionEngine();
          gui = new Interface(engine);
          engine.setGUI(gui);
public class Interface {
     // A bunch of methods that set up the gui
     // And then my progress bar method
     public void updateProgressBar(int value){
          bar.setValue(value);
public class EvolutionEngine {
     public void start() {
          For (int i=0; i<x; i++)
               // Do a bunch of stuff
               // then update progress bar
               gui.updateProgressBar(i);
}

Answer 1

Thanks for the reply.
The run() method works great now, and threads well with the progress bar.
However, I can't seem to start it up again after the run() method has completed (i.e. pressing "run" on my gui, which calls engine.start() does nothing the second time around).
The method run() has definately quit, and, as an experiment, I threw in a stop() command for good measure. Nothing.
When I switch the threaded method for my original method, everything works fine (except it doesn't thread), so it's obviously something to do with the thread.
Any suggestions as to why I don't seem to be able to call start() twice, when the first one should certainly have quit?
Thanks!