code: public void setThumbnail(String src) {
          setImage(src);
          if (imageElem != null) {
              imageElem.removeClassName("jqm4gwt-listitem-icon");
              imageElem.addClassName("jqm4gwt-listitem-thumb");
          }
      }
docs: Sets the image to be used to the given source url.
  <br> The same as setImage(), but image is marked as thumbnail class.