Calculate number of weekdays between two dates in Java

Question

public static int getWorkingDaysBetweenTwoDates(Date startDate, Date endDate) {
    Calendar startCal = Calendar.getInstance();
    startCal.setTime(startDate);        

    Calendar endCal = Calendar.getInstance();
    endCal.setTime(endDate);

    int workDays = 0;

    //Return 0 if start and end are the same
    if (startCal.getTimeInMillis() == endCal.getTimeInMillis()) {
        return 0;
    }

    if (startCal.getTimeInMillis() > endCal.getTimeInMillis()) {
        startCal.setTime(endDate);
        endCal.setTime(startDate);
    }

    do {
       //excluding start date
        startCal.add(Calendar.DAY_OF_MONTH, 1);
        if (startCal.get(Calendar.DAY_OF_WEEK) != Calendar.SATURDAY && startCal.get(Calendar.DAY_OF_WEEK) != Calendar.SUNDAY) {
            ++workDays;
        }
    } while (startCal.getTimeInMillis() < endCal.getTimeInMillis()); //excluding end date

    return workDays;
}

Start date and end date are exclusive, Only the days between given dates will be counted. Start date and end date will not be included.

Solution without loop:

static long days(Date start, Date end){
    //Ignore argument check

    Calendar c1 = Calendar.getInstance();
    c1.setTime(start);
    int w1 = c1.get(Calendar.DAY_OF_WEEK);
    c1.add(Calendar.DAY_OF_WEEK, -w1);

    Calendar c2 = Calendar.getInstance();
    c2.setTime(end);
    int w2 = c2.get(Calendar.DAY_OF_WEEK);
    c2.add(Calendar.DAY_OF_WEEK, -w2);

    //end Saturday to start Saturday 
    long days = (c2.getTimeInMillis()-c1.getTimeInMillis())/(1000*60*60*24);
    long daysWithoutWeekendDays = days-(days*2/7);

    // Adjust days to add on (w2) and days to subtract (w1) so that Saturday
    // and Sunday are not included
    if (w1 == Calendar.SUNDAY && w2 != Calendar.SATURDAY) {
        w1 = Calendar.MONDAY;
    } else if (w1 == Calendar.SATURDAY && w2 != Calendar.SUNDAY) {
        w1 = Calendar.FRIDAY;
    } 

    if (w2 == Calendar.SUNDAY) {
        w2 = Calendar.MONDAY;
    } else if (w2 == Calendar.SATURDAY) {
        w2 = Calendar.FRIDAY;
    }

    return daysWithoutWeekendDays-w1+w2;
}

Solution without loop in 5 lines of code

Days between are defined in the same way as ChronoUnit.DAYS.between(start, end) which means there are 4 days between Monday and Friday. Since we are only interested in weekdays we have to subtract weekends, therefore from Friday until Tuesday there will be 2 weekdays(just compute endDay - startDay and subtract 2 for the weekend). Add 1 to the result if you want an inclusive result, i.e. not days between.

I present two solutions.

First solution (5-liner, short and cryptic):

import java.time.*;
import java.time.temporal.*;

public static long calcWeekDays1(final LocalDate start, final LocalDate end) {
    final DayOfWeek startW = start.getDayOfWeek();
    final DayOfWeek endW = end.getDayOfWeek();

    final long days = ChronoUnit.DAYS.between(start, end);
    final long daysWithoutWeekends = days - 2 * ((days + startW.getValue())/7);

    //adjust for starting and ending on a Sunday:
    return daysWithoutWeekends + (startW == DayOfWeek.SUNDAY ? 1 : 0) + (endW == DayOfWeek.SUNDAY ? 1 : 0);
}

Second solution:

public static long calcWeekDays2(final LocalDate start, final LocalDate end) {
    final int startW = start.getDayOfWeek().getValue();
    final int endW = end.getDayOfWeek().getValue();

    final long days = ChronoUnit.DAYS.between(start, end);
    long result = days - 2*(days/7); //remove weekends

    if (days % 7 != 0) { //deal with the rest days
        if (startW == 7) {
            result -= 1;
        } else if (endW == 7) {  //they can't both be Sunday, otherwise rest would be zero
            result -= 1;
        } else if (endW < startW) { //another weekend is included
            result -= 2;
        }
    }

    return result;
}

I used Shengyuan Lu's solution, but I needed to make a fix for the case where the method is called when one of the dates is on a Saturday and the other a Sunday - otherwise the answer is off by a day:

static long days(Date start, Date end){
    //Ignore argument check

    Calendar c1 = GregorianCalendar.getInstance();
    c1.setTime(start);
    int w1 = c1.get(Calendar.DAY_OF_WEEK);
    c1.add(Calendar.DAY_OF_WEEK, -w1 + 1);

    Calendar c2 = GregorianCalendar.getInstance();
    c2.setTime(end);
    int w2 = c2.get(Calendar.DAY_OF_WEEK);
    c2.add(Calendar.DAY_OF_WEEK, -w2 + 1);

    //end Saturday to start Saturday 
    long days = (c2.getTimeInMillis()-c1.getTimeInMillis())/(1000*60*60*24);
    long daysWithoutSunday = days-(days*2/7);

    if (w1 == Calendar.SUNDAY) {
        w1 = Calendar.MONDAY;
    }
    if (w2 == Calendar.SUNDAY) {
        w2 = Calendar.MONDAY;
    }
    return daysWithoutSunday-w1+w2;
}