code: @Override
      public int compareTo(MonthDay other) {
          int cmp = (month - other.month);
          if (cmp == 0) {
              cmp = (day - other.day);
          }
          return cmp;
      }
docs: Compares this month-day to another month-day.
  <p>
  The comparison is based first on value of the month, then on the value of the day.
  It is "consistent with equals", as defined by {@link Comparable}.
  
  @param other  the other month-day to compare to, not null
  @return the comparator value, negative if less, positive if greater