code: public void setType(CheckBoxType type) {
          this.type = type;
          switch (type) {
              case FILLED:
                  Element input = DOM.getChild(getElement(), 0);
                  input.setAttribute("class", CssName.FILLED_IN);
                  break;
              case INTERMEDIATE:
                  addStyleName(type.getCssName() + "-checkbox");
                  break;
              default:
                  addStyleName(type.getCssName());
                  break;
          }
      }
docs: Setting the type of Checkbox.