Allow focus after disabling JTextField

Question

I have a form with several textfields. Two textfields are mutually exclusive; you can modify one or the other, but not both. Upon edit of one, I disable the other. This works perfectly. My problem is the tab order disappears upon disabling the textfield. If I edit fieldA, fieldB is appropriately disabled upon focusLost of fieldA. I can use the tab key multiple times, but focus is never set to another component on the form. How can I get around this?
Here's the sample code:
      fieldA.addFocusListener(
            new FocusAdapter()
               public void focusLost(FocusEvent focusEvent)
                     JTextField field = (JTextField)focusEvent.getSource();
                     // if the value was changed, disallow editing in trade field
                     String newValue = field.getText();
                     if (!newValue.equalsIgnoreCase(original))
                        fieldB.setEnabled(false);
                     // need else block in case the user changes the value, then changes it back to the original value
                     else
                        fieldB.setEnabled(true);
         );

Answer 1

public void focusLost(FocusEvent e)
     if (textField2 == e.getOppositeComponent())
          textField2.transferFocus();
     textField2.setEnabled( false );
}