Java code to calculate number of mid nights (00:00:00) in a date range

Question

I am trying to write a java block to find the number of mid-nights in a particular date range.

For example:

begin date: 05/01/2014 00:00:00 end date : 05/03/2014 00:00:00

this range has 3 mid-nights in it.

or

begin date : 05/01/2014 00:00:00 end date : 05/02/2014 23:59:59

this has only one.

It basically has to tell me how many times the time "00:00:00" occurrs in the date range. Please help me out. I tried many approaches but none work correct.

Answer 1

I would just count the days (the actual dates), and add one if the earliest date has a time of 00:00:00.

begin date: 05/01/2014 00:00:00 end date : 05/03/2014 00:00:00

• 03 - 01 = 2 days.
• Since the begin date has a time of 00:00:00, then add one:
• 2 + 1 = 3 midnights.

or

begin date : 05/01/2014 00:00:00 end date : 05/02/2014 23:59:59

• 02 - 01 = 1 day.
• Since the begin date has a time of 00:00:00, then add one:
• 1 + 1 = 2 midnights.

Also,

begin date : 5/01/2014 23:59:59 end date : 5/02/2014 00:00:01

• 02 - 01 = 1 day.
• Since the begin date doesn't have a time of 00:00:00, then don't add one:
• 1 midnight.

Answer 2

One option is to use Joda-Time library:

DateTimeZone zone = DateTimeZone.forID("America/New_York");

int days = Days.daysBetween(new DateTime(startDate, zone), new DateTime(endDate, zone)).getDays();

I think this is the easiest way. The drawback is that you need one more library..

Hope this can help!

Answer 3

The answer using Joda-Time is not correct. As @khriskooper has noted the count of midnights between

2014-05-01 00:00:00 and 2014-05-02 23:59:59

is not one but two midnights!

So here the correction using Joda-Time (not tested), but it could also be any other library which supports day-range calculations (not true for old Java-pre8). I leave out the timezone detail because I do not consider it as really relevant for the question. If OP wants he can replace LocalDateTime by DateTime and apply a timezone.

LocalDateTime ldt1 = new LocalDateTime(2014, 5, 1, 0, 0, 0);
LocalDateTime ldt2 = new LocalDateTime(2014, 5, 2, 23, 59, 59);

int days = Days.daysBetween(ldt1.toLocalDate(), ldt2.toLocalDate()).getDays();
if (ldt1.toLocalTime().equals(new LocalTime(0, 0))) {
  days++;
}

Answer 4

Using Joda's DateTime library (one I would recommmend anyway), an elegant way to do so would be:

private int getNumberOfNights(DateTime start, DateTime end) {
    int nightCount = 0;
    DateTime tempEnd = new DateTime(end);

    while (tempEnd.withTimeAtStartOfDay().isAfter(start)) {
        nightCount++;
        tempEnd = tempEnd.minusDays(1);
    }

    return nightCount;
}

... or if you want to avoid a while loop:

private int getNumberOfNights(DateTime start, DateTime end) {
    int nightCount = Days.daysBetween(start, end).getDays();
    DateTime leftOver = new DateTime(end.minusDays(nightCount));

    if (leftOver.withTimeAtStartOfDay().isAfter(start)) {
        nightCount++;
    }

    return nightCount;
}

Answer 5

With Java 7

public long countDays(Date dtStart, Date dtEnd) {
    long startDay = TimeUnit.DAYS.convert(dtStart.getTime(), TimeUnit.MILLISECONDS)
    long endDay = TimeUnit.DAYS.convert(dtEnd.getTime(), TimeUnit.MILLISECONDS)

    return endDay - startDay
}