code: @Override
      public int compareTo(Years otherAmount) {
          int thisValue = this.years;
          int otherValue = otherAmount.years;
          return Integer.compare(thisValue, otherValue);
      }
docs: Compares this amount to the specified {@code Years}.
  <p>
  The comparison is based on the total length of the amounts.
  It is "consistent with equals", as defined by {@link Comparable}.
  
  @param otherAmount  the other amount, not null
  @return the comparator value, negative if less, positive if greater