Extend the JDialog class. Create your gui by setting the JDialog
contentPane or adding to it. Add a static method such as:

public static String getString(JFrame parent) {}

This method will be blocked when you call setVisible(true). Have a
global string value that is set by interaction with the user or a field
that has a string entered into it and return this string:

public class StringDialog extends JDialog {
    String globalString;

    public StringDialog(JFrame parent) {
        super(parent, true);
        //write gui code here
    }

    public static String getString(JFrame parent) {
        StringDialog strDialog = new StringDialog(parent);

        strDialog.pack();
        strDialog.setVisible(true);

        return globalString;
    }
}

Give your dialog a model, often a single object,
more generally an object graph. Bind the dialog's
UI compontent values to that object.

Read model values after the dialog has been closed
(modal), or access the model while the dialog is open
(non-modal).

-Karsten

Assuming you have an OK button on your dialog that you are using to
close, in the event listener for the button use
myDialog.setVisible(false);

Then you can read the fields from the dialog, even though it is no
longer displayed, at any time. No need to pass the object, just read
it.
/js