question: public Period plusMonths ( long monthsToAdd ) { if ( monthsToAdd == 0 ) { return this ; } return create ( years , Math . toIntExact ( Math . addExact ( months , monthsToAdd ) ) , days ) ; }
target:  Returns a copy of this period with the specified months added. <p> This adds the amount to the months unit in a copy of this period. The years and days units are unaffected. For example, "1 year, 6 months and 3 days" plus 2 months returns "1 year, 8 months and 3 days". <p> This instance is immutable and unaffected by this method call.