JComboBoxのItem選択をループ

Action up = new AbstractAction() {
  @Override public void actionPerformed(ActionEvent e) {
    int index = combo.getSelectedIndex();
    combo.setSelectedIndex((index == 0) ? combo.getItemCount() - 1 : index - 1);
  }
};
Action down = new AbstractAction() {
  @Override public void actionPerformed(ActionEvent e) {
    int index = combo.getSelectedIndex();
    combo.setSelectedIndex((index == combo.getItemCount() - 1) ? 0 : index + 1);
  }
};
ActionMap amc = combo.getActionMap();
amc.put("myUp", up);
amc.put("myDown", down);
InputMap imc = combo.getInputMap();
imc.put(KeyStroke.getKeyStroke(KeyEvent.VK_UP, 0), "myUp");
imc.put(KeyStroke.getKeyStroke(KeyEvent.VK_DOWN, 0), "myDown");