JDialog dispose question

Posted on 2003-03-24
Medium Priority
Last Modified: 2007-12-19
I have the following code:

public static void main(String[] args)
  JDialog myDialog = new JDialog((JFrame)null, true);

In the first line I make sure that the dialog is modal, this is to make sure dispose is not called before the dialog is hidden.
Then I show the dialog,
and then I dispose it.
Lastly I make a println.

What I would expect:
I would expect a dialog to appear on the screen, with the possibility to close it on the close button of the window (upper right corner in windows).
After I close the dialog, I would expect to see the message "Out" printed,
and lastly the program to terminate.

What is wrong:
The program does print "Out" after closing the dialog, but never terminates.

What am I missing here?

Slight modification I have tried, with the same result:
Before the show, I add:
myPanel has a button, and upon clicking it, the dialog is hidden, "Out" is printed, but the program doesn't terminate:
private void clickButtonQuit()
  Component comp = this;
  while (comp!=null && !(comp instanceof JDialog)) comp = comp.getParent();

  if (comp==null) return;


Question by:selsted
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LVL 35

Expert Comment

ID: 8194613
 You can always add a System.exit(0); at the end.
LVL 35

Expert Comment

ID: 8194638
 If you are using JDK1.4 you could also do that as well:


Author Comment

ID: 8194646
I should have mentioned that I show dialogs within my application, and this is a potential memory leak I want to fix.
So System.exit is not an option.

Accepted Solution

glottis earned 400 total points
ID: 8194797
when you show any type of JComponent a new thread is started.
JDialog myDialog = new JDialog((JFrame)null, true);

you are saying that myDialog has a parent null of type JFrame. so jvm starts a new thread for null frame (i think)

so therefore you have to type System.exit(0) after it prints out.


change it to meet girionis way:

public static void main(String[] args) {
 JDialog myDialog = new JDialog((JFrame)null, true);

the setDefaultCloseOperation method exists in jdk1.2.2 and above, only the constant EXIT_ON_CLOSE is in jdk1.3 and above.

Author Comment

ID: 8195067
Setting the close operation to EXIT_ON_CLOSE in 1.4.1 doesn't do anything, and according to the api, only DO_NOTHING, HIDE, and DISPOSE is possible to set.

After making some tests, I think I have figures out what happens in your (I think) comment.

Starting a program, counting the thread, and exiting gave a result of 4 threads. However counting the thread in my original problem gave a result of 6 threads. These 2 extra threads is surely the cause of why it is not terminating. My concern was more or less the memory leak (though other irrelevant problems occure from this problem). Making a loop where I created, showed, and disposed JDialogs as in the problem, I monitored the memory usage, and the number of threads. The memory did as it always does, increasing and decreasing, but the thread count stayed at 6.

Now I just have to figure out if other windows are present, so that I can make a System.exit if there isn't.

I accept your comment as the answer.


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