code: public static LocalDate adjustToLastDayOfWeek(LocalDate date, DayOfWeek firstDayOfWeek) {
          LocalDate startOfWeek = adjustToFirstDayOfWeek(date, firstDayOfWeek);
          return startOfWeek.plusDays(6);
      }
docs: Adjusts the given date to a new date that marks the end of the week where the
  given date is located. If "Monday" is the first day of the week and the given date
  is a "Wednesday" then this method will return a date that is four days later than the
  given date. This method calculates the first day of the week and then adds six days
  to it.
  
  @param date           the date to adjust
  @param firstDayOfWeek the day of week that is considered the start of the week ("Monday" in Germany, "Sunday" in the US)
  @return the date of the first day of the week
  @see #adjustToFirstDayOfWeek(LocalDate, DayOfWeek)
  @see DateControl#getFirstDayOfWeek()