SwingWorker done() is called before doInBackground is finished

Question

Hi,
I'm having a problem understanding how the SwingWorker works. According to java docs: "After the doInBackground method is finished the done method is executed" and there is a happens before relationship. But if I run the code below:
   public class A extends SwingWorker<Void, Void>
         protected Void doInBackground() throws InterruptedException
              String k = "this is a test";
              String j = k;
              while(true)
                   for(int i=0; i<1000; i++)
                        j = j + k;
                        j.replaceAll("nothing", "something");
                   System.out.println("going");
         protected void done()
              try
                   get();
              catch(InterruptedException ex){System.out.println("interrupted");}
              catch(CancellationException ex){System.out.println("cancelled");}
              System.out.println("done");
}and call cancel(true) while the thread is running the output I get is
going
going
cancelled
done
going
going
So that means that done() get's fired after I called cancel(), not after doInBackground() is finished.
This is causing some serious problems in my actual application, as I do some clean up in done(), but doInBackground() keeps going until it hits my Thread.sleep() code.
Thanks a lot.

Answer 1

Hello,
I think I have a workaround to your problem. By the way, I am the one who submitted [bug 6826514|http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6826514] in April of 2009.
My solution takes advantage of firePropertyChange() and related methods in SwingWorker.
Here I completely refrain from using done() method to detect the end of doInBackground()'s execution.
Please bear with me the fact that the code is a little bit long.
/* GoodWorker.java  */
package solve;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import javax.swing.SwingWorker;
* @author Sumudu
public class GoodWorker extends SwingWorker<Void, Void> {
    private MainFrame mainFrame = null;
    private final String prReallyDone = "ReallyDone";
    private void whenReallyDone() {
        mainFrame.afterWorkerFinishes();
        System.out.println("done");
    public GoodWorker(MainFrame mainFrame) {
        this.mainFrame = mainFrame;
        getPropertyChangeSupport().addPropertyChangeListener(prReallyDone,
            new PropertyChangeListener() {
            public void propertyChange(PropertyChangeEvent e) {
                if (e.getNewValue().equals(true)) {
                    whenReallyDone();
    protected Void doInBackground() throws Exception {
        String k = "this is a test";
        String j = k;
        while (!isCancelled()) {
            for (int i = 0; i < 1000; i++) {
                j = j + k;
                j.replaceAll("nothing", "something");
            System.out.println("going");
        firePropertyChange(prReallyDone, false, true);
        return null;
// -- The End --
/* BadWorker.java */
package solve;
import javax.swing.SwingWorker;
public class BadWorker extends SwingWorker<Void, Void> {
    private MainFrame mainFrame = null;
    public BadWorker(MainFrame mainFrame) {
        this.mainFrame = mainFrame;
    protected Void doInBackground() throws Exception {
        String k = "this is a test";
        String j = k;
        while (!isCancelled()) {
            for (int i = 0; i < 1000; i++) {
                j = j + k;
                j.replaceAll("nothing", "something");
            System.out.println("going");
        return null;
    @Override
    protected void done() {
        mainFrame.afterWorkerFinishes();
        System.out.println("done");
// -- The End --
/* MainFrame.java */
package solve;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.concurrent.CancellationException;
import java.util.concurrent.ExecutionException;
import javax.swing.SwingWorker;
public class MainFrame extends javax.swing.JFrame {
    private BadWorker badWorker = null;
    private GoodWorker goodWorker = null;
    private boolean useGoodWoker;
    private void initialize() {
        this.setLocationRelativeTo(null);
        btnStop.setEnabled(false);
        useGoodWoker = chkUseGoodWorker.isSelected();
        btnStart.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                chkUseGoodWorker.setEnabled(false);
                btnStart.setEnabled(false);
                btnStop.setEnabled(true);
                useGoodWoker = chkUseGoodWorker.isSelected();
                System.out.println("Starting SwingWorker...");
                if (useGoodWoker) {
                    goodWorker = new GoodWorker(MainFrame.this);
                    goodWorker.execute();
                } else {
                    badWorker = new BadWorker(MainFrame.this);
                    badWorker.execute();
        btnStop.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                SwingWorker worker = (useGoodWoker ? goodWorker : badWorker);
                if (worker != null && !worker.isDone()) {
                    btnStop.setEnabled(false);
                    worker.cancel(true);
    public void afterWorkerFinishes() {
        SwingWorker worker = (useGoodWoker ? goodWorker : badWorker);
        try {
            worker.get();
        } catch (InterruptedException ie) {
            System.out.println("Got interrupted while waiting in get().");
        } catch (ExecutionException ee) {
            System.out.print("An exception was thrown inside doInBackground(). ");
            Throwable t = ee.getCause();
            System.out.printf("More specifically, %s %n", t.getMessage());
        } catch (CancellationException ce) {
            System.out.println("SwingWorker got cancelled by you.");
        chkUseGoodWorker.setEnabled(true);
        btnStart.setEnabled(true);
    /** Creates new form MainFrame */
    public MainFrame() {
        initComponents();
        initialize();
    /** This method is called from within the constructor to
     * initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is
     * always regenerated by the Form Editor.
    // <editor-fold defaultstate="collapsed" desc=" Generated Code ">//GEN-BEGIN:initComponents
    private void initComponents() {
        chkUseGoodWorker = new javax.swing.JCheckBox();
        buttonPanel = new javax.swing.JPanel();
        btnStart = new javax.swing.JButton();
        btnStop = new javax.swing.JButton();
        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        setTitle("SwingWorkers");
        chkUseGoodWorker.setText("Check this to use Good Worker");
        chkUseGoodWorker.setBorder(javax.swing.BorderFactory.createEmptyBorder(0, 0, 0, 0));
        chkUseGoodWorker.setHorizontalAlignment(javax.swing.SwingConstants.CENTER);
        chkUseGoodWorker.setMargin(new java.awt.Insets(0, 0, 0, 0));
        getContentPane().add(chkUseGoodWorker, java.awt.BorderLayout.CENTER);
        btnStart.setText("Start");
        buttonPanel.add(btnStart);
        btnStop.setText("Stop");
        buttonPanel.add(btnStop);
        getContentPane().add(buttonPanel, java.awt.BorderLayout.SOUTH);
        pack();
    }// </editor-fold>//GEN-END:initComponents
     * @param args the command line arguments
    public static void main(String args[]) {
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new MainFrame().setVisible(true);
    // Variables declaration - do not modify//GEN-BEGIN:variables
    private javax.swing.JButton btnStart;
    private javax.swing.JButton btnStop;
    private javax.swing.JPanel buttonPanel;
    private javax.swing.JCheckBox chkUseGoodWorker;
    // End of variables declaration//GEN-END:variables
// -- The End --