code: private CheckBox getCheckBox(Object id) {
  
          if (!m_checkBoxes.containsKey(id)) {
              m_checkBoxes.put(id, new CheckBox());
          }
          return m_checkBoxes.get(id);
      }
docs: Gets the check box for the item with the given id.<p>
  
  @param id the item id
  @return the check box