JTableのセル中にJRadioButtonを配置

class RadioButtonsPanel extends JPanel {
  private final String[] answer = {
      Answer.A.toString(), Answer.B.toString(), Answer.C.toString()};
  public JRadioButton[] buttons;
  public ButtonGroup bg = new ButtonGroup();

  public RadioButtonsPanel() {
    super();
    setLayout(new BoxLayout(this, BoxLayout.X_AXIS));
    initButtons();
  }

  protected void initButtons() {
    bg = new ButtonGroup();
    buttons = new JRadioButton[answer.length];
    for (int i = 0; i < buttons.length; i++) {
      buttons[i] = new JRadioButton(answer[i]);
      buttons[i].setActionCommand(answer[i]);
      buttons[i].setFocusable(false);
      buttons[i].setRolloverEnabled(false);
      add(buttons[i]);
      bg.add(buttons[i]);
    }
  }

  protected void updateSelectedButton(Object v) {
    if (v instanceof Answer) {
      removeAll();
      initButtons();
      buttons[((Answer) v).ordinal()].setSelected(true);
      // switch ((Answer) v) {
      //   case A:
      //     buttons[0].setSelected(true);
      //     break;
      //   case B:
      //     buttons[1].setSelected(true);
      //     break;
      //   case C:
      //     buttons[2].setSelected(true);
      //     break;
      //   default:
      //     break;
      // }
    }
  }
}

class RadioButtonsRenderer extends RadioButtonsPanel implements TableCellRenderer {
  public RadioButtonsRenderer() {
    super();
    setName("Table.cellRenderer");
  }

  @Override public Component getTableCellRendererComponent(JTable table,
        Object value, boolean isSelected, boolean hasFocus, int row, int column) {
    updateSelectedButton(value);
    return this;
  }
}

class RadioButtonsEditor extends RadioButtonsPanel implements TableCellEditor {
  public RadioButtonsEditor() {
    super();
    ActionListener al = new ActionListener() {
      @Override public void actionPerformed(ActionEvent e) {
        fireEditingStopped();
      }
    };
    for (AbstractButton b: buttons) {
      b.addActionListener(al);
    }
  }

  @Override public Component getTableCellEditorComponent(JTable table,
        Object value, boolean isSelected, int row, int column) {
    updateSelectedButton(value);
    return this;
  }

  @Override public Object getCellEditorValue() {
    // bug: return bg.getSelection().getActionCommand();
    return Answer.valueOf(bg.getSelection().getActionCommand());
  }

  // Copied from AbstractCellEditor
  // protected EventListenerList listenerList = new EventListenerList();
  transient protected ChangeEvent changeEvent = null;
// ...