code: public static Date addDays(Date date, int days)
     {
        Calendar cal = popCalendar(date);
        cal.add(Calendar.DAY_OF_YEAR, days);
        Date result = cal.getTime();
        pushCalendar(cal);
        return result;   
     }
docs: Add a number of days to the supplied date.
  
  @param date start date
  @param days number of days to add
  @return  new date