java swingworker thread to update main Gui

There is an excellent example from the JavaDocs

class PrimeNumbersTask extends
        SwingWorker<List<Integer>, Integer> {

    PrimeNumbersTask(JTextArea textArea, int numbersToFind) {
        //initialize
    }

    @Override
    public List<Integer> doInBackground() {
        List<Integer> numbers = new ArrayList<Integer>(25);
        while (!enough && !isCancelled()) {
            number = nextPrimeNumber();
            numbers.add(number);
            publish(number);
            setProgress(100 * numbers.size() / numbersToFind);
        }

        return numbers;
    }

    @Override
    protected void process(List<Integer> chunks) {
        for (int number : chunks) {
            textArea.append(number + "\n");
        }
    }
}

JTextArea textArea = new JTextArea();
final JProgressBar progressBar = new JProgressBar(0, 100);
PrimeNumbersTask task = new PrimeNumbersTask(textArea, N);
task.addPropertyChangeListener(
 new PropertyChangeListener() {
     public  void propertyChange(PropertyChangeEvent evt) {
         if ("progress".equals(evt.getPropertyName())) {
             progressBar.setValue((Integer)evt.getNewValue());
         }
     }
 });

task.execute();
System.out.println(task.get()); //prints all prime numbers we have got

Take a look at publish and process

The underlying intention is that you need to update the UI from only within the Event Dispatching Thread, by passing the data you want to updated to the UI via the publish method, SwingWorker will call process for you within the context of the EDT