Re: A Swing question about readable control-flow

Daniele Futtorovic <>
Wed, 23 Jul 2008 14:54:39 +0200
On 23/07/2008 14:11, Leo Breebaart allegedly wrote:

I have a control-flow issue I was hoping to get some advice on.

In my Swing GUI, I have a button. If I click on that button, I
want, via its associated Action, but, and this is the kicker:
*depending on a certain condition*, to show and process the
results of a modal JDialog *before* I perform the actual action.
But the action should always run. It's just the showing of the
dialog that is dependent on outside context.

How I would *like* to implement this:

    public class MyAction extends AbstractAction
        public void actionPerformed(ActionEvent e)
            if (hasQuestionnaire)

        private void showQuestionnaire()
            final QuestionnaireDialog dialog = new QuestionnaireDialog();
            dialog.getCancelButton().addActionListener(new ActionListener()
                    public void actionPerformed(ActionEvent e)
                            // process cancel
            dialog.getSubmitButton().addActionListener(new ActionListener()
                    public void actionPerformed(ActionEvent e)
                            // process submit

This does not work, because the showQuestionnaire method will put
up the dialog without blocking, causing 'doStuff' to be executed
immediately afterwards, without waiting for the dialog to be

I can solve the issue by moving the doStuff() call into both of
the dialog's registered ActionListeners, *and* by placing the
MyAction's doStuff() call into an else-branch of the
if-statement, but all that multiplication of code (even if it's
just a single line) smells very wrong to me. It makes the actual
control flow a lot more difficult to follow.

Am I missing something simple? Does anybody have any advice on
how they would implement this cleanly?

Many thanks in advance,

Unless I'm mistaken, and if QuestionnaireDialog extends JDialog, then
you simply have to specify the dialog as /modal/ (see the Javadoc --
it's done in the c'tor). That way, the call to setVisible(true) will
*block* until the dialog is hidden; which means, in turn, you'll have to
add the listeners /prior/ to showing it.


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