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I have a JTable that will reload sorted data from the database when the user clicks on a column header. MainView (JFrame) contains the GUI elements that will create a new SwingWorker and start it. The SwingWorker's doInBackGround() function changes the cursor of the MainView to be the wait cursor. Then when the doInBackground() function is completed doing its work and before it leaves the doBackground function it changes the cursor back to the default cursor.

Sometimes the cursor shows up but after a while it stops showing the cursor each time I click on the header. It probably works the first few times and seems kind of random.

Why does the cursor show sometimes, but not others? Is there a particular way I should be setting the wait cursor? Should I set the wait cursor from the SwingWorker thread or from the MainView GUI thread?

Andrew Thompson
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Brian T Hannan
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3 Answers3

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You should set the wait cursor before the doinbackground. I've done that in the constructor of the worker thread class or right before calling execute. You need to set your cursor back to normal in the done method. That is probably where your problem is. The done method runs on the event dispatch thread, which must be used for UI updates.

Do not update any gui components from the doinbackground method or you will see this type of behavior. I didn't know that and did the same thing you are doing. It can be confusing.

Logan
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You may want to let your jtable sort the data instead of calling the database again. It's pretty easy to setup. table sorting

Logan
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  • I tried it, however, it doesn't do well with dates. I want a certain formatting for the dates shown and it doesn't sort them by timestamp properly in the desired format. I also have a filter button that will show a wait cursor as well where this same situation is occurring. – Brian T Hannan Feb 18 '12 at 06:02
  • Oh yeah, dates and JTables... I need the same thing in my program. You have to format the cells as Date objects instead of plain objects. I haven't gotten around to actually doing that part. I think you just define the column class for your table model for that column as a Date.class object. Then it treats it like a date value. I haven't gotten around to that myself though. – Logan Feb 18 '12 at 14:01
  • Logan I believe I did that too and it didnt work. I got the code working by making new calls to the db for now and will probably not change it because it would require too much retesting – Brian T Hannan Feb 20 '12 at 16:17
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From the Oracle's Swing Concurrency page:

Swing event handling code runs on a special thread known as the event dispatch thread. Most code that invokes Swing methods also runs on this thread. This is necessary because most Swing object methods are not "thread safe": invoking them from multiple threads risks thread interference or memory consistency errors.

The SwingWorker API page reports, about the doInBackground() method:

Computes a result, or throws an exception if unable to do so.

Then it's used from the worker to execute some tasks, executing on a worker thread.

and about the done() method:

Executed on the Event Dispatch Thread after the doInBackground method is finished. The default implementation does nothing. Subclasses may override this method to perform completion actions on the Event Dispatch Thread. Note that you can query status inside the implementation of this method to determine the result of this task or whether this task has been cancelled.

Commonly, it's used to display the final results after the doInBackground() completes its work.

Then, I think you should set the cursor on the doInBackground() SwingWorker method using code like:

public Void doInBackground() {
     setCursor(Cursor.getPredefinedCursor(Cursor.WAIT_CURSOR));
...
}

and deactivate it on the done() SwingWorker method, with:

public void done() {
 setCursor(Cursor.getDefaultCursor());
 ...
}

You can find other info about these cursor methods on the Cursor class API.

Here a page with some busy cursor code examples, here a SO question related to cursor.

Community
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Alberto Solano
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  • beware: simply setting the default cursor might not be good enough, some components have their own "default" or even more than one, depending on mouse location which makes it tricky to reset correctly: http://stackoverflow.com/questions/8830642/cursor-icon-does-not-change-after-trigerring-setcursor-method – kleopatra Feb 18 '12 at 10:19
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    I may be wrong, but I think making any changes to a component in the gui from the doInBackground() method could cause this type of problem. I would maybe suggest creating a constructor for the SwingWorkerThread class and putting the cursor code there, just to make sure it's doing it from the event dispatch thread. At least that is the approach I have taken in the past. We all know that changes with the more we learn though. – Logan Feb 18 '12 at 14:25
  • @kleopatra thanks for the clarification and the link, I didn't know about that problems. I thought, logically, if the OP wants the cursor appears after clicking on a column header, loading the SwingWorker, then the cursor should be set in doInBackground(). Now I know, with your link, that there are some problems :-) – Alberto Solano Feb 19 '12 at 11:03
  • @Logan Thank you for the comment, I read your answer, I understood what problem might be in my answer. – Alberto Solano Feb 19 '12 at 11:04
  • Setting in doinbackground didnt fix the issue ... I'll have to try the constructor next. – Brian T Hannan Feb 20 '12 at 16:19