code: public long roundCeiling(long instant) {
          long newInstant = roundFloor(instant);
          if (newInstant != instant) {
              instant = add(newInstant, 1);
          }
          return instant;
      }
docs: Round to the highest whole unit of this field. The value of this field
  and all fields of a higher magnitude may be incremented in order to
  achieve this result. The fractional millis that cannot be expressed in
  whole increments of this field are set to minimum.
  <p>
  For example, a datetime of 2002-11-02T23:34:56.789, rounded to the
  highest whole hour is 2002-11-03T00:00:00.000.
  <p>
  The default implementation calls roundFloor, and if the instant is
  modified as a result, adds one field unit. Subclasses are encouraged to
  provide a more efficient implementation.
  
  @param instant  the milliseconds from 1970-01-01T00:00:00Z to round
  @return rounded milliseconds