Re: cleaning up very carefully

Knute Johnson <>
Wed, 07 Dec 2011 06:31:13 -0800
On 12/6/2011 11:24 PM, Stefan Ram wrote:

   Executive Summary of my question: Can you dispose a Swing
   GUI component (or all of the Swing GUI) while processing an
   event generated from this very GUI component?

   More elaborated:

   You all know

frame.setDefaultCloseOperation( javax.swing.JFrame.EXIT_ON_CLOSE );

   , but I have found that the EDT (and thus the JVM) will also
   terminate once all disposable Swing components are disposed.

   So, when I get a ?QUIT? command (i.e., from the application menu),
   I dispose all Swing components, and the application exits. I like
   this, because when I forget to dispose a single Swing component
   in my cleanup, this error will immediatly be observable, because
   in this case, the application will not exit anymore.

   Now, I had no idea, whether it is OK to dispose the whole view of
   the Swing application, including the JFrame and the very QUIT
   menu entry whose message I am just processing during the processing
   of the message from that menu entry itself. When I will return to
   Swing, will Swing be shocked to learn that the GUI component
   whose message was just being processed does not exist anymore?
   Does it need this component to finish the processing of an event
   that was created by this component. (After all, a reference to
   the component might still be contained in the event.)

   So I tried to be very careful and do one indirection as follows:

if( message instanceof QuitMainCommand )
{ javax.swing.SwingUtilities.invokeLater
   ( new java.lang.Runnable()
     { public void run()
       { MainFrame.this.dispose(); }} ); }

   This is the code for the QUIT menu item. The ?MainFrame.this.dispose()?
   will dispose the JFrame and the menu including the QUIT menu item, whose
   message I am just processing. Because, I do not know whether this is
   legal, I call my dispose code indirectly via invokeLater. But is this
   really necessary?

   BTW: I am aware that ?instanceof? can be a code smell. I have designed
   a hierarchy of commands, and for the moment I am not aware of a better
   solution. I am (ab)using the Java class system to store a tree of
   commands, using ?instanceof? to test for subentries of a tree.

There is nothing wrong with putting the dispose() in a Listener or some
method that is running on the EDT. The program won't stop until the EDT
has exited which it will do once it returns from the method.


Knute Johnson

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