How to calculate difference ONLY in months using Java's Joda API

Question

I am writing a program that is supposed to just calculate the months between 2 given dates and return the value to the program. For instance, if I have to calculate the number of months between 1 April and 30 June (which is a quarter, 3 months), and I use the following code:

    DateTime start = new DateTime().withDate(2011, 4, 1);
    DateTime end = new DateTime().withDate(2011, 6, 30);

    Months mt = Months.monthsBetween(start, end);
    int monthDiff = mt.getMonths();

Using this, I am still getting "2" as the number of months, whereas it is actually "3" months. This is an example of what I want. I am only calculating the number of months (i.e. from 1st of the start month t the last date of the end month) and I dont need additional analysis like days, weeks, hours, etc. How do I achieve this?

Any help would be appreciated.

Can't wait to read the answer from Jon Skeet, the Stackoverflow and Date API expert ;) — DaveFar, Sep 18 '11 at 09:56
I believe the Yoda time answer is correct. From april 1st to (but not including) june 30th would be _almost_ 3 months. I think both dates have the same time (00:00) and thus june 30th isn't really included in the range. — extraneon, Sep 18 '11 at 19:18
@extraneon - Thats right. The Period displayed is 2 months, 4 weeks and 1 day. — Abhay Bhargav, Sep 19 '11 at 02:37

score 9 · Accepted Answer · answered Sep 18 '11 at 10:42

9

DateTime start = new DateTime().withDate(2011, 4, 1);
DateTime end = new DateTime().withDate(2011, 6, 30);
Period p = new Period(start, end, PeriodType.months().withDaysRemoved());
int months = p.getMonths() + 1;

You need the withDaysRemoved() part to ensure that adding one to the number of months works. Otherwise two dates such as 2011-04-15 and 2011-06-14 would still result in the answer being 2

answered Sep 18 '11 at 10:42

Brian Roach

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This seems to be working fine. I will do some more testing and check – Abhay Bhargav Sep 19 '11 at 02:35
This is not working. For instance, it fails for 2015-06-10 and 2015-07-01 ("months" ends up with 1 instead of 2). The correct solution can be found here: http://stackoverflow.com/a/1086432/1369016 – Bitcoin Cash - ADA enthusiast Jun 10 '15 at 02:26

Roland Illig · Answer 2 · 2011-09-18T10:50:37.383

3

Why do you expect the answer to be 3 months? The precise answer is two months and a little bit, which then results in the two months you are getting.

If you want the number of months that are “touched” by this interval, this is a completely different question. ~~Just add 1 to the result of the difference.~~

edited Sep 18 '11 at 10:50

answered Sep 18 '11 at 10:40

Roland Illig

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The problem there is that depending on the day provided, adding one to month might not work. – Brian Roach Sep 18 '11 at 10:43
I didn't mean to add one month to a date, but to add 1 to the `monthDiff` variable in the question. – Roland Illig Sep 18 '11 at 10:44
1

I know. If the dates were 2011-04-15 and 2011-06-14, that would fail because getMonths() would return 1. – Brian Roach Sep 18 '11 at 10:48

score 2 · Answer 3 · edited Jan 18 '12 at 21:32

2

Months mt = Months.monthsBetween(
    start.monthOfYear().roundFloorCopy(), 
    end.monthOfYear().roundCeilingCopy()
);

edited Jan 18 '12 at 21:32

javanna

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answered Sep 18 '11 at 12:17

buritos

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score 1 · Answer 4 · answered Oct 21 '13 at 09:36

DateTime start = new DateTime().withDate(2011, 4, 1);
        DateTime end = new DateTime().withDate(2011, 2, 1);
        Period p = new Period(start, end, PeriodType.months().withDaysRemoved());
        int months = p.getMonths();
        System.out.println(months);


wrong output in this case

lukastymo · Answer 5 · 2011-09-18T19:08:55.240

Joda algorithm counted correctly difference between this two dates. This pseudo-code will be the easiest way to explain how it works:

// (1)
monthsBetween(2011.6.14, 2011.4.15) = 1
monthsBetween(2011.6.15, 2011.4.15) = 2
// (2)
monthsBetween(2011.6.30, 2011.4.1) = 2
monthsBetween(2011.7.1,  2011.4.1) = 3

To do what you want you need to "improve" joda algorithm:

Count distance between two dates (use normal monthsBetween)
If you have specific situation: the last day of month in one date and the 1st day of month in second date, add +1 to the final result.

score 1 · Answer 6 · answered Sep 18 '11 at 10:51

1

Let y1 and m1 be the year and month of the start date, and y2 and m2 be the year and month of the end date. Then the number of months between start and end, including the months of the start and end dates is

(y2 - y1) * 12 + (m2 - m1) + 1

answered Sep 18 '11 at 10:51

Jiri Kriz

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How to calculate difference ONLY in months using Java's Joda API

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