Where to read/write properties in Swing application?

[Klaas van Gelder]

Hell, it is about 5 years ago I posted on this forum and haven't done any Java programming since 2 years.... But I have a new project again, and a very trivial problem.

I work on a program with a Swing GUI, and according to the guidelines, I start the GUI in the event dispatch thread. My main class is not GUI aware, I consider it as good practice to have aa non-Swing aware main class but maybe this idea is a bit obsolete...

public Diagnostics() {

   Properties appProperties = new Properties();

   //code for reading property file

  SwingUtilities.invokeLater(new Runnable() {
    public void run() {
       DiagnosticsView view = new DiagnosticsView(appProperties);
       view.setVisible(true);
    }
  });
}

public static void main(String[] args) {
  new Diagnostics();
}

Not very special, the issue is that the constructor of the main class returns immediately and the main object gets out of scope. Even the main() methods returns immediately so the main thread ends.

So there is not really a good place to place code to save the property file when the aplication is closed. Is the finalize() method maybe a good location? I do not think so, nor do I think the reading and writing of the property file belongs in the GUI classes.... In each case the reading and writing of the property file shoud occur in the same class I guess.
Obviously this is a trivial problem and solved more than a thousand times What do I miss here?
REgards, Klaas

[Rob Spoor]

Runtime.getRuntime.addShutdownHook(...)

This will always be called when the JVM shuts down except when:

you call Runtime.getRuntime().halt(...)

the JVM is forcefully terminated (using sigkill in Linux or from the processes tab of Windows' Task Manager). Terminating through sigclose (Linux) or from the applications tab of Windows' Task Manager does call them, as far as I know.

although I'm not 100% sure, I also believe shutdown hooks are not called when the JVM is terminated because Windows / Linux shuts down completely.

[Klaas van Gelder]

Thanks, this works indeed! Never seen that before.... I wonder if this is indeed the way most programs handle the writing of persistent data in standalone applications.