code: protected Date getExpirationDate(Date endDate, int daysToExpire) {
          Calendar calendar = Calendar.getInstance();
          calendar.setTime(endDate);
          calendar.add(Calendar.DATE, daysToExpire);
          return calendar.getTime();
      }
docs: Calculates the restore expiration date based on the restoration
  end date and the number of days before retirement
  
  @param endDate      date on which the restoration completed
  @param daysToExpire number of days the restored content should stay in place
  before it is retired
  @return expiration date of restored content