Output not appearing when using SwingWorker?

Question

Hi guys,
I'm desperate here. Any help would be great.
I'm using SwingWorker to append info into a Text Area, but when I run the code, nothing happens in the TextArea. Here's the code
public class RLGUIFrame extends javax.swing.JFrame implements ActionListener{
    private final GridBagConstraints constraints;
    JTextArea movementText;
    private final Border border =
        BorderFactory.createLoweredBevelBorder();
    private final JButton startButton, stopButton;
    private RobotTask robTask;
     public static final int GRID_SIZE=10;
     public static final int NUMBER_OF_TIMES=1000;
    private JTextArea makeText() {
        JTextArea t = new JTextArea();
        t.setEditable(false);
        t.setAlignmentX(RIGHT_ALIGNMENT);
        t.setBorder(border);
        getContentPane().add(t, constraints);
        return t;
    private JButton makeButton(String caption) {
        JButton b = new JButton(caption);
        b.setActionCommand(caption);
        b.addActionListener(this);
        getContentPane().add(b, constraints);
        return b;
    public RLGUIFrame() {
        super("RL");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        //Make text boxes
        getContentPane().setLayout(new GridBagLayout());
        constraints = new GridBagConstraints();
        constraints.insets = new Insets(3, 10, 3, 10);
        movementText = makeText();
        //Make buttons
        startButton = makeButton("Start");
        stopButton = makeButton("Stop");
        stopButton.setEnabled(false);
        //Display the window.
        pack();
        setVisible(true);
    private class LocReport{
         private Location loc;
         private double val, rand;
         private boolean KS;
         LocReport(Location L, double value, boolean KillSpot, double random){
              this.loc = L;
              this.val = value;
              this.KS = KillSpot;
              this.rand = random;
private class RobotTask extends SwingWorker<Void, LocReport> {
    @Override
    protected Void doInBackground() {
        Grid grid = new Grid( GRID_SIZE );
         Location startPosition = grid.getLoc( 8, 8 );
         Robot jerry = new Robot( startPosition );
         Random rand = new Random();
         grid.fillGrid();
        //EastWestSentry ews = new EastWestSentry( grid.getLoc(5, 5));
         grid.getLoc( 3 , 3 ).setValue( 1.0 );
         grid.getLoc( 7 , 7 ).setValue( 0.0 );
         for( int i = 0; i < GRID_SIZE; i++){
              grid.getLoc( i, 4 ).isKillSpot = true;
         grid.getLoc(4, 5).isWindy    = true;
         grid.getLoc(7, 5).isKillSpot = true;
         grid.getLoc( 6, 4 ).isKillSpot = false;
         for( int i=0; i < NUMBER_OF_TIMES; i++ ){
         while ( jerry.getLocation() != grid.getLoc( 3 , 3 ) ){
         Location L = jerry.getLocation();
         double value = L.value;
         double random = rand.nextDouble();
         boolean isKS = L.KillSpot();
         publish( new LocReport(L,value,isKS,random) );
          if(jerry.getLocation().isWindy == true)
               jerry.move( grid.getLoc(7, 5) );
          if( jerry.getLocation().hasSentry )
                    jerry.getLocation().isKillSpot = true;     
          if(jerry.getLocation().isKillSpot == true){
               if( rand.nextDouble() > 0.5 ){
                    System.out.printf("Lucky this time. This killspot didn't kill me.\n");
               }else{
               grid.getLoc(jerry.getXCoord(), jerry.getYCoord()).setValue(-1);
               jerry.regenerate( startPosition );
          if(rand.nextDouble()>0.8){
               System.out.printf("I'm going exploring!\n");
               jerry.exploratoryMove();
          else{
               //ews.patrol();
               jerry.move();
               if( jerry.getMyPreviousLocation().isKillSpot &&
                    jerry.getMyPreviousLocation().getValue() > 0.0 ){
                    jerry.getMyPreviousLocation().setValue(-1);
         return null;
    protected void process(List<LocReport> locs) {
         LocReport location = locs.get( locs.size() - 1);
         movementText.append("========================\n");
         movementText.append("Robot is at location : " + location.loc.getXCoord() +
                               ", " + location.loc.getYCoord() + "\n");
         movementText.append("It's value is : " + location.val + "\n");
public void actionPerformed(ActionEvent e) {
    if ("Start" == e.getActionCommand()) {
        startButton.setEnabled(false);
        stopButton.setEnabled(true);
        (robTask = new RobotTask()).execute();
    } else if ("Stop" == e.getActionCommand()) {
        startButton.setEnabled(true);
        stopButton.setEnabled(false);
        robTask.cancel(true);
        robTask = null;
    * @param args the command line arguments
    public static void main(String args[]) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                new RLGUIFrame();
}Edited by: zimmerPlease on Mar 23, 2010 3:58 PM

Answer 1

You're adding both components with the same GridBagConstraints without setting any of its attributes. Follow the link to the Swing tutorial efrom the topic listing page for this forum and click through to the Layouts section where you can learn how to use GridBagLayout and GridBagConstraints properly.
As an aside, there is no need to extend JFrame to create a GUI that has to show a JFrame. Favor composition over inheritance. And in this case, it leads to add(...) coode being all over the place where it can't be easily found.
db