JComboBoxのアイテムを選択不可にする

class DisableItemComboBox<E> extends JComboBox<E> {
  private final Set<Integer> disableIndexSet = new HashSet<>();
  private boolean isDisableIndex;
  private final Action up = new AbstractAction() {
    @Override public void actionPerformed(ActionEvent e) {
      int si = getSelectedIndex();
      for (int i = si - 1; i >= 0; i--) {
        if (!disableIndexSet.contains(i)) {
          setSelectedIndex(i);
          break;
        }
      }
    }
  };
  private final Action down = new AbstractAction() {
    @Override public void actionPerformed(ActionEvent e) {
      int si = getSelectedIndex();
      for (int i = si + 1; i < getModel().getSize(); i++) {
        if (!disableIndexSet.contains(i)) {
          setSelectedIndex(i);
          break;
        }
      }
    }
  };

  public DisableItemComboBox() {
    super();
  }

  public DisableItemComboBox(ComboBoxModel<E> aModel) {
    super(aModel);
  }

  public DisableItemComboBox(E[] items) {
    super(items);
  }

  @Override public void updateUI() {
    super.updateUI();
    setRenderer(new DefaultListCellRenderer() {
      @Override public Component getListCellRendererComponent(
          JList list, Object value, int index,
          boolean isSelected, boolean cellHasFocus) {
        Component c;
        if (disableIndexSet.contains(index)) {
          c = super.getListCellRendererComponent(
              list, value, index, false, false);
          c.setEnabled(false);
        } else {
          c = super.getListCellRendererComponent(
              list, value, index, isSelected, cellHasFocus);
          c.setEnabled(true);
        }
        return c;
      }
    });
    ActionMap am = getActionMap();
    am.put("selectPrevious3", up);
    am.put("selectNext3", down);
    InputMap im = getInputMap();
    im.put(KeyStroke.getKeyStroke(KeyEvent.VK_UP, 0), "selectPrevious3");
    im.put(KeyStroke.getKeyStroke(KeyEvent.VK_KP_UP, 0), "selectPrevious3");
    im.put(KeyStroke.getKeyStroke(KeyEvent.VK_DOWN, 0), "selectNext3");
    im.put(KeyStroke.getKeyStroke(KeyEvent.VK_KP_DOWN, 0), "selectNext3");
  }

  public void setDisableIndex(Set<Integer> set) {
    disableIndexSet.clear();
    for (Integer i: set) {
      disableIndexSet.add(i);
    }
  }

  @Override public void setPopupVisible(boolean v) {
    if (!v && isDisableIndex) {
      isDisableIndex = false;
    } else {
      super.setPopupVisible(v);
    }
  }

  @Override public void setSelectedIndex(int index) {
    if (disableIndexSet.contains(index)) {
      isDisableIndex = true;
    } else {
      // isDisableIndex = false;
      super.setSelectedIndex(index);
    }
  }
}