code: public final boolean adjacent(final DateRange range) {
          boolean adjacent = false;
          if (rangeStart.equals(range.getRangeEnd())) {
              adjacent = true;
          } else if (rangeEnd.equals(range.getRangeStart())) {
              adjacent = true;
          }
          return adjacent;
      }
docs: Decides whether these periods are serial without a gap.
  @param range a period to test for adjacency
  @return true if one period immediately follows the other, false otherwise