Catch-22: need to assign a local variable within an anonymous class

Question

static boolean showMessage(Window parent, String button0, String button1)
    throws HeadlessException {
          final Window w = new Window(parent);
          Panel p = new Panel(new GridBagLayout());
          final Button b[] = new Button[]{new Button(button0), (button1 != null) ? new Button(button1) : (Button)null};
          boolean rval[]; //tristate: null, true, false
          w.setSize(100, 50);
          w.setVisible(true);
          //add b[0
          gbc.fill = GridBagConstraints.HORIZONTAL;
          gbc.gridx = 0;
          gbc.gridy = 3;
          p.add(b[0], gbc);
          //add b[1]
          if (button1 != null) {
               gbc.fill = GridBagConstraints.HORIZONTAL;
               gbc.gridx = 1;
               gbc.gridy = 3;
               p.add(b[1], gbc);
          w.add(p);
          w.pack();
        w.setVisible(true);
        //actionListener for button 0
          b[0].addActionListener(new ActionListener() {
                    public void actionPerformed(ActionEvent e) {
                         if (e.getSource() == b[0]) {
                              w.setVisible(false);
                              rval = new boolean[1];
                              rval[0] = true;
          //actionListener for button 1
          if (button1 != null) {
               b[1].addActionListener(new ActionListener() {
                         public void actionPerformed(ActionEvent e) {
                              if (e.getSource() == b[1]) {
                                   w.setVisible(false);
                                   rval = new boolean[1];
                                   rval[0] = false;
        while (true) {
             try {
                  if (rval[0] == true || rval[0] == false) //should trigger NullPointerException
                       return rval[0];
             } catch (NullPointerException e) { }
     }catch-22 is at
rval = new boolean[1];
rval = false;javac whines: "local variable rval is accessed from within inner class; needs to be declared final"
How do I assign to rval if it's declared final?
Or at the very least, how do I get rid of this error (by all means, hack fixes are okay; this is not C/C++, I don't have to use sanity checks)?
I'm trying to make a messagebox in java without using JOptionPane and I'm trying to encapsulate it in one method.
And I'm far too lazy to make a JNI wrapper for GTK.

Answer 1

dcminter wrote:
How do I assign to rval if it's declared final?You don't and you can't. You're not allowed to assign to the local variable of the outer class for extremely good reasons, so forget about trying.
Or at the very least, how do I get rid of this errorIf you don't want the side effect, then just use an inner class variable or a local variable.
If you want the side effect then use a named class and provide it with a getter and setter.
Finally, in this specific case because you're using an array object reference, you could probably just initialise the array object in the outer class. I.e.
// Outer class
final boolean[] rval = new boolean[1];
// Anonymous Inner class
rval[0] = true; // No need to intialize the array.
I declared it as an array so that it would be a tristate boolean (null, true, false) such that accessing it before initialization from the actionPerformed would trigger a NullPointerException.
Flowchart:
is button pressed? <-> no
|
V
Yes->set and return
Is there a way to accomplish this without creating a tribool class?