Adding one month to date fails using Joda-Time DateTime in Java

Question

I tried to add full months from a given start date by using java DateTime and method plusMonths().

When my start time is at the beginning of a month, everything works like expected:

DateTime startOfMonth = new DateTime(2013, 1, 1, 00, 00, 00);
    System.out.println(startOfMonth.toString());
    for (int i = 0; i < 12; i++) {
        startOfMonth = startOfMonth.plusMonths(1);
        System.out.println(startOfMonth.toString());
}

The output is the first day of every month like expected and everything is great!

2013-01-01T00:00:00.000+01:00
2013-02-01T00:00:00.000+01:00
2013-03-01T00:00:00.000+01:00
2013-04-01T00:00:00.000+02:00
2013-05-01T00:00:00.000+02:00
2013-06-01T00:00:00.000+02:00
2013-07-01T00:00:00.000+02:00
2013-08-01T00:00:00.000+02:00
2013-09-01T00:00:00.000+02:00
2013-10-01T00:00:00.000+02:00
2013-11-01T00:00:00.000+01:00
2013-12-01T00:00:00.000+01:00
2014-01-01T00:00:00.000+01:00

But when I change my example to the end of a month it doesn't return what I want!

System.out.println("");
DateTime endOfMonth = new DateTime(2012, 12, 31, 23, 59, 59);
System.out.println(endOfMonth.toString());
for (int i = 0; i < 12; i++) {
    endOfMonth = endOfMonth.plusMonths(1);
    System.out.println(endOfMonth.toString());
}

This returns:

2012-12-31T23:59:59.000+01:00
2013-01-31T23:59:59.000+01:00
2013-02-28T23:59:59.000+01:00
2013-03-28T23:59:59.000+01:00
2013-04-28T23:59:59.000+02:00
2013-05-28T23:59:59.000+02:00
2013-06-28T23:59:59.000+02:00
2013-07-28T23:59:59.000+02:00
2013-08-28T23:59:59.000+02:00
2013-09-28T23:59:59.000+02:00
2013-10-28T23:59:59.000+01:00
2013-11-28T23:59:59.000+01:00
2013-12-28T23:59:59.000+01:00

So, why is "2013-02-28T23:59:59.000+01:00" plus one month not "2013-03-31T23:59:59.000+01:00"? Where are these three days?

Probably you need to handle the case of February specifically. As the the answer below suggest that is the way DateTime behaves. — mawia, Nov 01 '13 at 09:11
Here is the proper way of getting last day of the month: http://stackoverflow.com/questions/9711454/how-to-get-the-last-date-of-a-particular-month-with-jodatime — Admit, Nov 01 '13 at 09:13
@Gatschet What behavior do you desire? The behavior you see is what the documentation promised for method [plusMonths()](http://www.joda.org/joda-time/apidocs/org/joda/time/DateTime.html#plusMonths(int)). — Basil Bourque, Nov 01 '13 at 09:39
Now i see my problem. If i talk to someone on the 28th of February we will meet us in one month, i am referring to the 28th of march! Not the 31th of march.... — Gatschet, Nov 01 '13 at 09:48

Aaron Digulla · Accepted Answer · 2013-11-01T09:42:02.830

The problem with date operations is that months have different number of days. In January, you have 31 days, February has only 28. If you add "one month" to January 31st, the software can't guess what you want to achieve, so it adds increments the month which gives you February, 31st - which isn't valid. The next step is then to reconcile the date which yields these odd results that you're seeing.

Note: In the original Java Date classes, you'd get 2nd or 3rd of March after adding one month to January which isn't exactly better :-)

The correct way to iterate over the end of month is to iterate over the first day of then month and the subtract one day (or one millisecond):

DateTime startOfMonth = new DateTime(2013, 1, 1, 00, 00, 00);
System.out.println(startOfMonth.toString());
for (int i = 0; i < 12; i++) {
    startOfMonth = startOfMonth.plusMonths(1);
    DateTime endOfMonth = startOfMonth.minusDays(1); // magic here
    System.out.println(startOfMonth + "-" + endOfMonth);
}

If you just need a date range, use an half open range [start,end) where end is always the first of a month.

or minus one second/milli-second – Peter Lawrey Nov 01 '13 at 09:12 — Peter Lawrey, Nov 01 '13 at 09:12

score 4 · Answer 2 · answered Nov 01 '13 at 09:07

4

Because there's only 28 days in Februar 2013. So when you're adding one month after, it will keep to be the 28th of each month.

This is specified in the doc :

The calculation will do its best to only change the month field retaining the same day of month. However, in certain circumstances, it may be necessary to alter smaller fields. For example, 2007-03-31 plus one month cannot result in 2007-04-31, so the day of month is adjusted to 2007-04-30.

answered Nov 01 '13 at 09:07

Alexis C.

91,686
21
171
177

My problem is, i have a application with a start and end time and a resolution for some bins to show some data. For example I can choose 1.1.2013 00:00:00 to 1.1.2014 00:00:00 with a resolution of month. Now I can see some data for every month in a bin. This settings will be stored in a template with localtime. The problem occurs when somebody is using the same template in a different timezone. Then the start time and end time is for example 31.12.2012 23:00:00 to 31.12.2013 23:00:00 (-1 hour).... – Gatschet Nov 01 '13 at 12:38
... This is no problem for January and February. But the month march will only have 28 days, because 28.2.2013 plus one month result in 28.3.2013! In this way the customer doesn't have full month... – Gatschet Nov 01 '13 at 12:39

score 1 · Answer 3 · answered Nov 01 '13 at 09:11

You can't change to february the 31 and there is no way for the object to remember you meant the last day of the month rather than the 28th.

Instead I suggest you use the first day of each month and subtract one milli-second. This way the calculation will worth out the way you want.

score 1 · Answer 4 · answered Nov 03 '13 at 04:38

As mentioned in a comment above, the Joda way for getting the last day of the month is to get the maximum value on the dayOfMonth property.

public static void endOfMonth() {
    DateTime startOfMonth = new DateTime(2013, 1, 1, 00, 00, 00);

    for (int i = 0; i < 12; i++) {
        int lastDay = startOfMonth.dayOfMonth().getMaximumValue();
        System.out.println(startOfMonth.withDayOfMonth(lastDay).toString());

        startOfMonth = startOfMonth.plusMonths(1);
    }
}

This produces:

2013-01-31T00:00:00.000-06:00
2013-02-28T00:00:00.000-06:00
2013-03-31T00:00:00.000-05:00
2013-04-30T00:00:00.000-05:00
2013-05-31T00:00:00.000-05:00
2013-06-30T00:00:00.000-05:00
2013-07-31T00:00:00.000-05:00
2013-08-31T00:00:00.000-05:00
2013-09-30T00:00:00.000-05:00
2013-10-31T00:00:00.000-05:00
2013-11-30T00:00:00.000-06:00
2013-12-31T00:00:00.000-06:00

Basil Bourque · Answer 5 · 2015-01-21T22:43:35.053

Half-Open

Your Question is an example of why tracking a span of time is usually best done using the "half-open" approach. In Half-Open ( notation: [) ), the beginning if the time span is inclusive while the ending is exclusive. So "a month" means the first moment of the first day of the month and running up to but not including the first moment of the first day of the following month.

The Joda-Time library offers a class to represent such spans of time, Interval.

DateTimeZone timeZone = DateTimeZone.forID( "Europe/Zurich" );
DateTime firstOfYear = new DateTime( 2013, 1, 1, 0, 0, 0, timeZone ).withTimeAtStartOfDay();
Interval month01_Interval = new Interval( firstOfYear, firstOfYear.plusMonths( 1 ).withTimeAtStartOfDay() );

When run:

month01_Interval : 2013-01-01T00:00:00.000+01:00/2013-02-01T00:00:00.000+01:00

score 0 · Answer 6 · answered Nov 01 '13 at 09:13

0

You can use java Calendar object if you want to work with date and time. Read about java Calendar object and you can make this work.

for example in Calendar object you can do this:

Calendar cal = Calendar.getInstance();
cal.setTime(new Date());

cal.add(Calendar.MONTH, 1);

answered Nov 01 '13 at 09:13

Shahe Masoyan

157
4
4
14

I replaced in my example DateTime with java.util.Calendar but the result is the same! cal.add(Calendar.MONTH, 1) from "2013-02-28T23:59:59.000+01:00" is still "2013-03-28T23:59:59.000+01:00" – Gatschet Nov 01 '13 at 09:25

score 0 · Answer 7 · answered Nov 01 '13 at 10:00

This works for me:

public static void main(String[] args) {
    Calendar endOfMonth = Calendar.getInstance();
    endOfMonth.set(Calendar.DAY_OF_MONTH, 31);
    endOfMonth.set(Calendar.MONTH, 11);
    endOfMonth.set(Calendar.YEAR, 2012);

    endOfMonth.set(Calendar.HOUR_OF_DAY, 23);
    endOfMonth.set(Calendar.MINUTE, 59);
    endOfMonth.set(Calendar.SECOND, 59);
    endOfMonth.set(Calendar.MILLISECOND, 59);

    System.out.println(endOfMonth.getTime());
    for (int i = 0; i < 12; i++) {
        endOfMonth.add(Calendar.MONTH, 1);

        if(i >= 2){
            endOfMonth.add(Calendar.MONTH, 1);
            endOfMonth.set(Calendar.DAY_OF_MONTH, 1);
            endOfMonth.add(Calendar.DAY_OF_MONTH, -1);
        }

        System.out.println(endOfMonth.getTime());
    }
}

and the result is:

Mon Dec 31 23:59:59 GMT+04:00 2012
Thu Jan 31 23:59:59 GMT+04:00 2013
Thu Feb 28 23:59:59 GMT+04:00 2013
Sun Mar 31 23:59:59 GMT+04:00 2013
Tue Apr 30 23:59:59 GMT+04:00 2013
Fri May 31 23:59:59 GMT+04:00 2013
Sun Jun 30 23:59:59 GMT+04:00 2013
Wed Jul 31 23:59:59 GMT+04:00 2013
Sat Aug 31 23:59:59 GMT+04:00 2013
Mon Sep 30 23:59:59 GMT+04:00 2013
Thu Oct 31 23:59:59 GMT+04:00 2013
Sat Nov 30 23:59:59 GMT+04:00 2013
Tue Dec 31 23:59:59 GMT+04:00 2013

score 0 · Answer 8 · answered May 06 '14 at 07:00

The best solution for such calculations I think is to fix the original seed date and keep incrementing the number of months to add as you loop through. That way you won't keep accumulating any adjustments as you go along. Try this:

    System.out.println("");
    DateTime endOfMonth = new DateTime(2012, 12, 31, 23, 59, 59);
    System.out.println(endOfMonth.toString());
    for (int i = 0; i < 12; i++) {
        DateTime newEndOfMonth = endOfMonth.plusMonths(i+1);
        System.out.println(newEndOfMonth.toString());
    }

score 0 · Answer 9 · answered Jun 18 '14 at 06:27

0

Add one day before incrementing the month, and subtract one day afterwards:

new DateTime(date).plusDays(1).plusMonths(months).minusDays(1).toDate()

answered Jun 18 '14 at 06:27

lbos

19
1

Adding one month to date fails using Joda-Time DateTime in Java

9 Answers9

Half-Open