Re: Starting a Swing application the Right Way

Thomas Hawtin <>
Fri, 09 Jun 2006 21:15:57 +0100
<4489d64c$0$945$> wrote:

I'm currently starting my swing application like this:

public static final void main(final String[] args) throws Exception {
  final MyApplication myApp = new MyApplication();

The MyApplication constructor should not create Swing components. I
would put this within the run method.

  EventQueue.invokeLater(new Runnable() {
    public final void run() {

final isn't useful here.

      myApp.showInterface(); // builds JFrame etc.

Note two things:

1. I am doing all Swing work on the EDT.
2. I am not calling System.exit().

These are both guidelines that Sun has espoused in the past.

This is all fine and good, but at least under unit testing my main()
method completes almost instantaneously and the program exits.

This makes a *certain* amount of sense to me--in my main() method, I'm
on my main thread, and its only job is to call
EventQueue.invokeLater(), after which it is, as far as it's concerned,
all done, so hey, control exits and the VM exits. This implies? I
guess? that the EDT is a daemon thread?

Almost. If it was a daemon thread and there was just a window open, the
process would exit. Not good. What I believe happens (in recent versions
of Sun's implementation) is that the EDT terminates after a short time
of there being no realised windows and no queued events.

Anyhow, is this Really And Truly The Way To Start A Swing Application?

Pretty much.

I noticed that Scott Violet has quite a nasty little hack in a proposed class
that serves to register background threads and actively monitors the
EventQueue to see if it's empty before doing some notifyAll() tricks.
Must I do all of this silliness just to start my application up in the
correct way?

No. The vast majority of that class is about shutting down the application.

It's nice to let the VM exit when there are no daemon threads left.
Unfortunately, it's all too common for some pesky idle thread or window
to stick around.

Tom Hawtin
Unemployed English Java programmer

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