Re: Swing in different 2 threads

From:

Thomas Hawtin <usenet@tackline.plus.com>

Newsgroups:

comp.lang.java.programmer

Date:

Fri, 15 Sep 2006 15:29:06 +0100

Message-ID:

<450ab8ae$0$2698$ed2619ec@ptn-nntp-reader02.plus.net>

dimitrik107@hotmail.com wrote:

I had interview question. She asked me if you have 2 threads and you
have class extending from the JFrame you can safely display class from
each thread or not and why? I do not know answer. I know recomendation
is to work with Swing from only main thread. Can someone explain me
answer to such question? Thank you for this help.

If you've got a class extending JFrame, you are probably extending
classes inappropriately. But apparently bad coding is fine for GUI
applications...

Unless stated otherwise, all Swing components should be accessed from
the AWT Event Dispatch Thread (EDT). They are not thread-safe (in fact
they are thread-hostile).

Note the EDT is not the main thread.

To be really pedantic:

The subclass of JFrame could add methods that are thread-safe. Perhaps a
method that calls setVisible from the correct thread (using
EventQueue.invokeLater/invokeAndWait).

In applets and JNLP/WebStart you will have more than one EDT in the same
JVM instance. As you said class, you could have two instances of the
same class on different EDTs (class loaders permitting).

Tom Hawtin
--
Unemployed English Java programmer
http://jroller.com/page/tackline/