code: public static String diff(IChemObject first, IChemObject second) {
          IDifference diff = difference(first, second);
          if (diff == null) {
              return "";
          } else {
              return diff.toString();
          }
      }
docs: Compare two {@link IChemObject} classes and return the difference as a {@link String}.
  
  @param first  the first of the two classes to compare
  @param second the second of the two classes to compare
  @return a {@link String} representation of the difference between the first and second {@link IChemObject}.