Question

I have a JFrame that shows a preview content, since the loading of preview data could take several times i decided to put the loading operation into a SwingWorker, here’s a code sample :

public void setPreviewContent(final String content) {

SwingWorker<Void, Void> worker = new SwingWorker<Void, Void>() {

    @Override
    protected Void doInBackground() throws Exception {

        frame.setCursor(java.awt.Cursor.getPredefinedCursor(
            java.awt.Cursor.WAIT_CURSOR));
        //DO My Work
        return null;
    }

    @Override
    protected void done() {
         frame.setCursor(java.awt.Cursor.getPredefinedCursor(
         java.awt.Cursor.DEFAULT_CURSOR));
    }
};
worker.execute();
}

My frame it is initialized each time that is shown and is disposed each time that is closed with :

frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

After the initialization and that is show the setPreviewContent() method is called and it work properly, the only problem is that each time i close and reopen the preview frame a Daemon Thread is created and is left running :

As you can see soon a huge number of threads remain in running state, causing a leak.
How can i resolve the problem ?

If i use a standard Thread i don’t have this problem …

Answer 1

The JavaDoc says:

Schedules this SwingWorker for execution on a worker thread. There are
a number of worker threads available. In the event all worker threads
are busy handling other SwingWorkers this SwingWorker is placed in a
waiting queue.

Did you try to close and reopen it more than 6 times, to see, whether eventually no new Thread is added? My guess is that you didn’t reach the thread pool limit yet.