orderedFocusTraversal
Makes this container a focus-cycle root whose Tab order follows its children's focusTraversalIndex values (ascending), rather than their on-screen geometry. Children without an index are visited after the indexed ones. Requires a JComponent target.
Only the order changes: which components Tab stops on stays Swing's own judgement. A control is a stop exactly where it would be in a hand-written form, so captions, layout containers and anything that cannot take the keyboard are stepped over. focusable declares that judgement for the component it is applied to.