code: public static PeriodType weeks() {
          PeriodType type = cWeeks;
          if (type == null) {
              type = new PeriodType(
                  "Weeks",
                  new DurationFieldType[] { DurationFieldType.weeks() },
                  new int[] { -1, -1, 0, -1, -1, -1, -1, -1, }
              );
              cWeeks = type;
          }
          return type;
      }
docs: Gets a type that defines just the weeks field.
  
  @return the period type