Java GUI Freezes even with SwingWorker

Question

I'm trying to use a SwingWorker to perform a lengthy task and update a JLabel with the result:

button.addActionListener(new ActionListener() {

    @Override
    public void actionPerformed(ActionEvent arg0) {
        new SwingWorker<String, Void>() {

            @Override
            protected String doInBackground() throws Exception {
                return doCalculation();
            }

            protected void done() {
                try {
                    label.setText(get());
                } catch (InterruptedException e) {
                    System.out.println("thread was interrupted");
                } catch (ExecutionException e) {
                    System.out.println("there was an ExecutionException");
                }
            }

        }.execute();

    }

});

I can click the button many times as I like and the Gui will remain responsive until two threads are finished at which point the Gui freezes while threads are running. If I only run one thread at a time, this problem still occurs.

I'd be greatful if anyone could point out if I am using the SwingWorker incorrectly or if there is another problem I'm not aware of. Thanks for your time. Ian

Edit

The doCalculation() is just something time consuming:

private String doCalculation() {
    for (int i = 0; i < 10000000; i++) {
        Math.pow(3.14, i);
    }
    return threads++ + "";
}

I don't see anything obviously wrong with the code you've posted so far, but I think key here is what is going on in the `doCalculation();` method. Can you post this code? — Hovercraft Full Of Eels, Jul 30 '11 at 14:53

score 6 · Accepted Answer · edited Jul 30 '11 at 15:59

I'm sorry, but even with your doCalculate() method, I'm still not able to reproduce your problem. For example here is my sscce:

import java.awt.event.*;
import java.util.concurrent.ExecutionException;
import javax.swing.*;

public class FooGui {
   private static int threads = 0;

   private static void createAndShowUI() {
      final JLabel label = new JLabel("      ");
      JButton button = new JButton("Button");
      button.addActionListener(new ActionListener() {

         @Override
         public void actionPerformed(ActionEvent arg0) {
            new SwingWorker<String, Void>() {

               @Override
               protected String doInBackground() throws Exception {
                  return doCalculation();
               }

               @Override
               protected void done() {
                  try {
                     label.setText(get());
                  } catch (InterruptedException e) {
                     System.out.println("thread was interrupted");
                  } catch (ExecutionException e) {
                     System.out.println("there was an ExecutionException");
                  }
               }
            }.execute();
         }
      });
      JPanel panel = new JPanel();
      panel.add(button);
      panel.add(label);

      JFrame frame = new JFrame("FooGui");
      frame.getContentPane().add(panel);
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.pack();
      frame.setLocationRelativeTo(null);
      frame.setVisible(true);
   }

   private static String doCalculation() {
      for (int i = 0; i < 5000000; i++) {
         Math.pow(3.14, i);
      }
      return threads++ + "";
   }

   public static void main(String[] args) {
      java.awt.EventQueue.invokeLater(new Runnable() {

         @Override
         public void run() {
            createAndShowUI();
         }
      });
   }
}

You may wish to create and post a "Short, Self Contained, Correct (Compilable), Example" or SSCCE of your own (please check the link). I'll bet that in the process of creating this, you'll probably find the problem and its solution yourself. If so, please be sure to come back here and let us know.

I know that this is not really an answer, but there's no way to post code like this in a comment.

Thank you for help, I appreciate it. I found the same freezing in your example as well so I experimented with it. Running from eclipse/command line reproduces this. I created a runnable jar and it runs perfectly. I'm running 64-bit Windows 7. I tried it with Ubuntu and that seems to fix the problem as well. Thanks again. — Ian, Jul 30 '11 at 15:52
I'm never see that inside Listener, I'm not sure with put..., but your post, that's probably possible way, nice example, no performance problems +1 — mKorbel, Jul 30 '11 at 15:55
@Ian: Hm, it would still be nice to know why the freezing occurs in those certain circumstances. Perhaps it has to do with too many threads. I've heard that there are times when dealing with multiple threads when you can't use a SwingWorker but instead would need to use an ExecutorService and a thread pool. — Hovercraft Full Of Eels, Jul 30 '11 at 15:57
I was having similar problems with my application, and running it via IDE is the problem for me also. — Joel Christophel, Jun 04 '13 at 22:06

Java GUI Freezes even with SwingWorker

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