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Java Forum / General / September 2006Swing in different 2 threads
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. > 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  SignatureUnemployed English Java programmer http://jroller.com/page/tackline/ > If you've got a class extending JFrame, you are probably extending > classes inappropriately. But apparently bad coding is fine for GUI > applications... Thank you for answer it is more clear now. I don't understand this point about extendin classed inappropriately? Most sample code for Swing tutorial has class MyFrame extends JFrame {...} Are you saying the tutorial code are probably extending classes inappropriately? > Thank you for answer it is more clear now. I don't understand this > point about extendin classed inappropriately? Most sample code for > Swing tutorial has class MyFrame extends JFrame {...} Are you saying > the tutorial code are probably extending classes inappropriately? Yes, that's what Thomas is saying. He's right, too. SignatureChris Smith >> If you've got a class extending JFrame, you are probably extending >> classes inappropriately. But apparently bad coding is fine for GUI [quoted text clipped - 4 lines] > Swing tutorial has class MyFrame extends JFrame {...} Are you saying > the tutorial code are probably extending classes inappropriately? Yes. See Effective Java, Item 14: Favor composition over inheritance. Indeed almost all of the code should not be dependent on being in a JFrame. There's two main motivations for this: Firstly, you want to keep your code as simple as possible, so don't involve inheritance. A secondary point is that you may want to move your JFrame contents to, say, a JInternalFrame, a JDialog, a JSplitPane, a JApplet, a JFrame subclassed for some genuine purpose, another layer of panels between frame and your contents, or something you haven't thought of yet. Tom Hawtin SignatureUnemployed English Java programmer http://jroller.com/page/tackline/ Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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