Overriding windowClosing(Window Event e)???

Question

Hello,
I have a similar question to some already posted regarding closing frames and panels. I am currently writing an application using Java as the interface an Access as the backend. I have the option to exit through a Jmenu. This allows me to prompt the user to save their changes before closing.
My problem is I want the user to have the same option when using the X button in the top right hand corner.
At the minute I am using the code below, which ends the application immediately, without allowing me time to save any changes first.
     fl.addWindowListener(new WindowAdapter()
public void windowClosing(WindowEvent e)
System.exit(0);
Can anyone offer me a better solution; I would ideally like to be able to load a JoptionPane with a YES_NO_OPTION to confirm if to save, followed by a second to confirm Exit, which is how the Jmenu option works.
Thanks for any help in advance.
Kris Dowse

Answer 1

What your code actually does: it intercepts the window is closing event, and as soon as it arrives, it kills the Java Virtual Machine (that's what System.exit() does).
Instead of the System.exit() call, you should let your option pane to appear. If it's modal (what I think it is), then I'd say you should run it in another thread, because you're supposed to return from an event handling method as soon as possible. The best is if you have a method which is invoked both from the action listener of the File/Exit menu item, and the window closing listener of the JFrame. This method should create a new thread, doing the work inside, and return immediatelly. If the user (inside the new thread) chooses to cancel the exit, then the thread simply stops, and your application runs. If the user chooses to really exit, then just call the System.exit(), that will kill all the active threads and stop the JVM. This is the behaviour you're seeking for, aren't you?
However, I'd think you also should set the JFrame's setDefaultCloseOperation to DO_NOTHING_ON_CLOSE.