private static void addFocusArrowListener(JComponent jc) {
        /**
         * Check to see if someone already added this kind of listener:
         */
        KeyListener[] listeners = jc.getKeyListeners();
        for (KeyListener listener : listeners) {
            if (listener instanceof FocusArrowListener) {
                return;
            }
        }
        // Add our own:
        jc.addKeyListener(new FocusArrowListener());
    }