如何显示两个日期之间的所有星期一？

Question

Im trying display all Mondays between two dates but I have no idea how to do it. I want ask user to input two dates using Scanner, to output all Mondays.

    String s = "2020-07-20";
    String e = "2020-09-20";
    LocalDate start = LocalDate.parse(s);
    LocalDate end = LocalDate.parse(e);
    List<LocalDate> totalDates = new ArrayList<>();

    while (!start.isAfter(end)) {
        totalDates.add(start);
        start = start.plusDays(1);

    }

Answer 1

To get the the first Monday, use:

LocalDate monday = start.with(TemporalAdjusters.nextOrSame(DayOfWeek.MONDAY));

Now you have to deal with an edge case: What if there is no Monday between start and end ? That would mean that the Monday computed here is after end :

if (monday.isAfter(end)) {
    totalDates = List.of();
}

After that, you can get a sequence of Mondays with the convenient datesUntil method:

totalDates = monday.datesUntil(end, Period.ofWeeks(1)).collect(Collectors.toList());

Note that datesUntil does not include the end date. If you need the end date included, pass in end.plusDays(1) .

Answer 2

You can use .getDayOfWeek() to get DayOfWeek and compare with DayOfWeek.MONDAY

while (!start.isAfter(end)) {
    if(start.getDayOfWeek().equals(DayOfWeek.MONDAY)) {
        totalDates.add(start);
    }
    start = start.plusDays(1);
}

And optimization is use start.plusWeeks(1) instead of start.plusDays(1) and you need to get the next monday before.

start = start.with(TemporalAdjusters.nextOrSame(DayOfWeek.MONDAY));
while (!start.isAfter(end)) {
    if(start.getDayOfWeek().equals(DayOfWeek.MONDAY)) {
        totalDates.add(start);
    }
    start = start.plusWeeks(1);
}

Answer 3

You need to use getDayOfWeek() , here is the solution:

import java.time.DayOfWeek;
import java.time.LocalDate;
import java.util.ArrayList;
import java.util.List;

public class AllMondays {
    public static void main(String[] args) {
        String s = "2020-07-20";
        String e = "2020-09-20";
        LocalDate start = LocalDate.parse(s);
        LocalDate end = LocalDate.parse(e);
        List<LocalDate> totalDates = new ArrayList<>();

        LocalDate nextMonday = start;
        int daysToAdvance = 1;
        while (!nextMonday.isAfter(end)) {
            if (nextMonday.getDayOfWeek() == DayOfWeek.MONDAY) {
                daysToAdvance = 7;
                totalDates.add(nextMonday);
            }
            nextMonday = nextMonday.plusDays(daysToAdvance);
        }
        System.out.println(totalDates);
    }
}

Answer 4

Here "find_day" is the day you want to find in date range

SimpleDateFormat format1 = new SimpleDateFormat("dd-MM-yyyy", Locale.getDefault());
            Date sub_start_date = format1.parse("01-06-2021");
            Date enddate = format1.parse("30-06-2021");
    
            Calendar min_date_c = Calendar.getInstance();
            min_date_c.setTime(sub_start_date);
            Calendar max_date_c = Calendar.getInstance();
            max_date_c.setTime(enddate);
    
            for (Calendar loopdate = min_date_c; min_date_c.before(max_date_c); min_date_c.add(Calendar.DATE, 1), loopdate = min_date_c) {
                int dayOfWeek = loopdate.get(Calendar.DAY_OF_WEEK);
                // if (dayOfWeek == Calendar.MONDAY || dayOfWeek == Calendar.SATURDAY) {
                if (dayOfWeek == find_day) {
                    Calendar[] disabledDays = new Calendar[1];
                    disabledDays[0] = loopdate;
                    Date newdate = loopdate.getTime();
                    String strDate = format1.format(newdate);
                    Log.e("DATES>>> ", "" + strDate);
                }
            }