🚀 go-pugleaf

Hi
I have got a class like this:

class MyClass {
    MyFrame frame;
    MyDialog dialog;

    MyClass() { ...  }

    public void showFrame() {
        if (frame != null) frame = new MyFrame();
    }

    public void showDialog() { // called from main()
        if (frame != null) {
            dialog = new MyDialog();
            dialog.show();
        }
    }

    //Inner class MyFrame
   class MyFrame extends Frame {
   ... // contents not important
   }

   //Inner class MyDialog
   class MyDialog extends Dialog {
       //constructor
       MyDialog() {
        super(frame, "Title", true /*modal*/ );  // <=== Compiler fails
here saying "cant reference variable frame
                                                                  //
before super class constructor is called; frame is always a valid
                                                                  //
pointer before dialog is called.
      }
   }
}

But if I pass to MyDialog constructor the frame it works fine. In code
it looks like:
    //constructor
    MyDialog(Frame f) {
        super(f, "Title", true); // <== this works fine
    }

what does the error mean and more importantly why is it an error, can
some one explain?
Thanks
Vasu