Java 7 get number of days between 2 dates with correct calculation for leap years

Question

I've seen many examples on Java 7 how to calculate days between 2 dates but I have found out that they do not include leap years correctly.

I've seen this example, but apparently leap years are not included:

Calculating days between two dates with in java

So I would like to see correct Java code how to get number of days without using Joda Time and Java 8?

The easiest way would be to convert your Gregorian date to a Julian day number. This is described [on Wikipedia](https://en.wikipedia.org/wiki/Julian_day#Converting_Julian_or_Gregorian_calendar_date_to_Julian_day_number). Once you have the Julian day number for both dates, subtract them. — Andy Turner, May 13 '16 at 08:25
No, sorry, the easiest way would be to use Jodatime or Java 8 :) — Andy Turner, May 13 '16 at 08:27
I mentioned I am interested in Java 7. I am using Java 7 for my work for specific reasons. — DarioBB, May 13 '16 at 09:16
Use Julian days, and you could do it in any version of Java. — Andy Turner, May 13 '16 at 09:41
Before java.time framework arrived in Java 8 (and [back-ported to Java 6 & 7](http://www.threeten.org/threetenbp/)), there was no built-in way to truly represent a date-only value sans time-of-day & time zone. For such a value, see the [`java.time.LocalDate`](http://docs.oracle.com/javase/8/docs/api/java/time/LocalDate.html) class. So there is no clean simple answer for you using old code, as seen in the comments on the [Answer by tamas rev](http://stackoverflow.com/a/37204352/642706). Those old date-time classes were supplanted by java.time classes for a reason (actually, *many* reasons). — Basil Bourque, May 13 '16 at 18:49

score 0 · Accepted Answer · edited May 23 '17 at 11:47

0

What about this arithmetic?

package com.example;

import java.text.SimpleDateFormat;
import java.util.Date;

public class DayDifference {

    public static void main(String[] args) throws Exception {
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
        Date d1 = sdf.parse("2016-02-28");
        Date d2 = sdf.parse("2016-03-01");

        long diff = (d2.getTime() - d1.getTime()) / (1000 * 60 * 60 * 24);

        System.out.println("diff: " + diff);
    }
}

This outputs 2, so works well with leap years.

Update: According to Andreas's comment you're better of with the +12h hack because it handles the daylight saving too: (d2.getTime() - d1.getTime() + 1000 * 60 * 60 * 12) / (1000 * 60 * 60 * 24)

edited May 23 '17 at 11:47

Community

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answered May 13 '16 at 07:55

Tamas Rev

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But doesn't work when crossing Daylight Saving Time. Says there are `0` days between `2016-03-13` and `2016-03-14` (America/New_York). – Andreas May 13 '16 at 07:58
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Since inputs are pure dates, and DST is never 12+ hours, this can be fixed by making the division rounding, i.e. add half a day: `(d2.getTime() - d1.getTime() + 1000 * 60 * 60 * 12) / (1000 * 60 * 60 * 24)` – Andreas May 13 '16 at 08:04
That gives '1' on my machine (CET/CEST). Anyway, we need full specification for what do we consider as 'one day difference'. E.g. what should be the difference between `2016-03-13 23:12:05` and `2016-03-14 00:17:44` ? – Tamas Rev May 13 '16 at 08:05
If the interpretation is that a "date" doesn't have a time-of-day, i.e. is a "pure" date like your code example has it, then it is a non-issue. – Andreas May 13 '16 at 08:07

Java 7 get number of days between 2 dates with correct calculation for leap years

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