Number of months between 2 java.util.Date, excluding day of month

Question

I want the number of months between 2 java.util.Date's, without the days in month counted. So I just want the year and month in the comparison.

Example:

 monthsBetween(new Date(2012,01,28), new Date(2012,02,01)) ---> 1

 monthsBetween(new Date(2012,02,27), new Date(2012,02,28)) ---> 0

 monthsBetween(new Date(2012,03,28), new Date(2012,07,01)) ---> 4

I have tried this (returns 0, expected 1), using Joda-time:

private static int monthsBetween(final Date fromDate, final Date toDate) {
    DateTime date1 = new DateTime().withDate(2012, 1, 20);
    DateTime date2 = new DateTime().withDate(2012, 2, 13);
    PeriodType monthDay = PeriodType.yearDayTime().withDaysRemoved();
    Period difference = new Period(date1, date2, monthDay);
    int months = difference.getMonths();
    
    return months;
 }

And also this (same results), using Joda-time:

private static int monthsBetween(final Date fromDate, final Date toDate) {
        return Months.monthsBetween(new DateTime(fromDate), new   DateTime(toDate).getMonths();
    }

How can I accomplish this?

Answer 1

You're asking for the number of whole months - which isn't the same as saying "ignore the day of month part".

To start with, I'd suggest using LocalDate instead of DateTime for the computations. Ideally, don't use java.util.Date at all, and take your input as LocalDate to start with (e.g. by parsing text straight to that, or wherever your data comes from.) Set the day of month to 1 in both dates, and then take the difference in months:

private static int monthsBetweenIgnoreDays(LocalDate start, LocalDate end) {
    start = start.withDayOfMonth(1);
    end = end.withDayOfMonth(1);
    return Months.monthsBetween(start, end).getMonths();
}

Answer 2

This version is JDK Calendar based:

public static void main(String[] args) throws Exception {
    SimpleDateFormat f = new SimpleDateFormat("yyyy-MM-dd");
    Date d1 = f.parse("2012-01-01");
    Date d2 = f.parse("2012-02-02");
    int n = differenceInMonths(d1, d2);
    System.out.println(n);
}

private static int differenceInMonths(Date d1, Date d2) {
    Calendar c1 = Calendar.getInstance();
    c1.setTime(d1);
    Calendar c2 = Calendar.getInstance();
    c2.setTime(d2);
    int diff = 0;
    if (c2.after(c1)) {
        while (c2.after(c1)) {
            c1.add(Calendar.MONTH, 1);
            if (c2.after(c1)) {
                diff++;
            }
        }
    } else if (c2.before(c1)) {
        while (c2.before(c1)) {
            c1.add(Calendar.MONTH, -1);
            if (c1.before(c2)) {
                diff--;
            }
        }
    }
    return diff;
}