JFrame freezes during while loop

Question

I am working on a Java program, which reads text files does some probability calculations. Reading files and all related calculations are done in a while loop.

I had created a GUI using JFrame, where i had added a Progress bar (using JProgressBar) to show the progress since the program takes a while to process the files.

The code looks like -

while( there are more files to read )
{
    Read this file ;
    Do calculations ;

    Update progress bar ;
}

Now, the problem is once the while loop starts and the first file is processed, the JFrame simply freezes. The progress bar does not get updated and i cannot press any button in the JFrame. Once the while loop ends the frame is updated and the progress bar is updated to its final value (hence, the progress bar starts from 0 then pauses then finally goes to 100).

Could some one explain why is the JFrame freezing ? Is it possible to update it (progress bar in the JFrame) in the while loop iterations ?

Thanks !

Please read [Concurrency in Swing](http://docs.oracle.com/javase/tutorial/uiswing/concurrency/). — mre, Apr 03 '13 at 13:21
See also this related [example](http://stackoverflow.com/a/4637725/230513). — trashgod, Apr 03 '13 at 15:23

Uwe Plonus · Accepted Answer · 2013-04-03T13:42:37.580

3

You're doing your time intense task in the event dispatch thread (EDT). This is a bad idea as the EDT also updates the UI. Therefore if this thread is blocked no update to the UI is done.

edited Apr 03 '13 at 13:42

answered Apr 03 '13 at 13:22

Uwe Plonus

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score 2 · Answer 2 · edited May 23 '17 at 11:55

2

The solution is to use threads, that's the reason because you're getting freeze, you're doing everything at the same time.

Please, look:

edited May 23 '17 at 11:55

Community

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answered Apr 03 '13 at 13:26

Castiblanco

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not incorrect, but not the whole story either: all swing-view-related access must happen on a particular thread, the ominous EDT :-) – kleopatra Apr 03 '13 at 14:19

score 1 · Answer 3 · answered Apr 03 '13 at 13:22

1

A thread can only do one thing at a time. So if you let it do calculations it will not update the gui. So you should use another thread. Also you will probably need to repaint your gui.

answered Apr 03 '13 at 13:22

WereWolfBoy

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If you use another thread to read files you don't need to repaint manually as this is normally done by the EDT. – Uwe Plonus Apr 03 '13 at 13:24
Ah cool. Wasn't sure. I have had problems with repainting in the past, so I thought I'd just mention it. – WereWolfBoy Apr 03 '13 at 13:26

JFrame freezes during while loop

3 Answers3

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