code: public List<String> getLabels() {
          if (labels != null && !labels.isEmpty())
              return labels;
          else {
              List<String> result = new ArrayList<>();
              for (long x = 0; x < counter.get(); x++)
                  result.add(formatLabel(x));
              return result;
          }
      }
docs: This method returns the list of labels used by this generator instance.
  If external list os labels was used as source, whole list will be returned.
  
  @return list of labels