Question

I’m making a simple game in Java using swing and am having problems with my GUI freezing up sporadically (due to threading issues most probably) after a button press that is supposed to trigger a switch in JPanels.

I posted a related thread here, which has more details about the actual code I’m currently using (although I did update the countdown and get that working fine). From answers to that thread, it seems like usingSwingUtilities.invokeLater() or invokeAndWait() might be what I need to solve the problem, but I’m not sure where in my code it is necessary or exactly how to implement it.

I don’t know that much about threading and could use any help (preferably somewhat detailed and with some sample code) that I can get. Let me know if any further details would be useful.

Answer 1

See: Tutorial: Concurrency in Swing

Generally speaking, the Event Dispatch Thread is a single thread, chugging through the event queue, processing one at a time.

SwingUtilities.invokeLater(..) 

puts a Runnable on this queue. So it will be processed by the EDT when the EDT finishes everything on the queue before it (This is why sleeping on the queue blocks other events like repainting). It’s relatively unusual to call invokeLater(..) from the EDT itself, though there are situations where it is useful (usually as a hack). I don’t think I have had a legitimate use for SwingUtilities.invokeAndWait(..) in the last 6 years. Maybe once.

javax.swing.Timer can be configured to fire once or periodically. When it fires, it puts an event on the EDT queue. If you have computationally-intensive processing that need to be done, consider using javax.swing.SwingWorker to do the computation on another thread, and give you back the result in a thread-safe manner (this is also comparatively rare).