Focus should switch between each of the 12 buttons using tab key automatically - if that is all you have in your GUI... are there other components? Especially text components - these have to recognize the tab key as text input - not focus switching. If this is the case, try doing a requestFocus() on the first button when the GUI/Panel is first displayed - you may also need to customize focus traversal.
Write once, run anywhere, because there's nowhere to hide! - /. A.C.