public  class DayOfWeek {

public static void main(String[] args) {

LocalDate from=LocalDate.now().plusDays(20);

java.time.DayOfWeek date=from.getDayOfWeek();

LocalDate day1=from.with(TemporalAdjusters.previous(java.time.DayOfWeek.SUNDAY));

LocalDate day2=from.with(TemporalAdjusters.previous(java.time.DayOfWeek.SUNDAY)).plusDays(1);

LocalDate day3=from.with(TemporalAdjusters.next(java.time.DayOfWeek.MONDAY)).minusDays(1);

System.out.println(from);／／隨便擬定一個日期

System.out.println(date);／／求出這個日期是星期幾

System.out.println(day1);／／求出這個日期所在周的上一星期的星期日（日歷一般第一天是周日開始）

System.out.println(day2);／／求出這個日期所在周的星期一

System.out.println(day3);／／求出這個日期所在周的星期日

}

}