Calculate month difference in Joda Time

Question

At the 4th line of code (ignore whitespace & comments) and beyond I'm calculating the month difference between 2 dates. This works, but looks a bit hacky. Is there a better way?

int handleAllowance(LocalDate today) {

    int allowance = membership.allowance();
    if (allowance == 0) return 0;

    // if update was last month (or earlier)
    int months = today.monthOfYear().getMaximumValue() - today.monthOfYear().getMinimumValue(); // yeah, 12, but just to be 100% correct :-)
    int curMonth = (today.getYear()               * months) + today.              getMonthOfYear();
    int updMonth = (lastAllowanceUpdate.getYear() * months) + lastAllowanceUpdate.getMonthOfYear();
    if (curMonth > updMonth) {

        // ...and if today is on or past update day
        int updateDay = Math.min(allowanceDay, today.dayOfMonth().getMaximumValue());
        if (today.getDayOfMonth() >= updateDay) {

            // number of months to give allowance (in the rare case this process fails to run for 2 months or more)
            int allowanceMonths = curMonth - updMonth;

            // give credits
            final int totalAllowance = allowance * allowanceMonths;
            giveCredits(totalAllowance);

            // update day
            lastAllowanceUpdate = lastAllowanceUpdate.plusMonths(allowanceMonths);

            // return the allowance given
            return totalAllowance;

        }

    }

    return 0;
}

Solution 1

Months.monthsBetween(
     start.withDayOfMonth(1),
     end.withDayOfMonth(1)).getMonths()

Solution 2

This is pretty similar to Bozho's solution:

  public static YearMonth toYearMonth(LocalDate localDate) {
    return new YearMonth(localDate.getYear(), localDate.getMonthOfYear());
  }

  public static int monthSwitches(LocalDate date1,LocalDate date2) {
    return Months.monthsBetween(toYearMonth(date1),toYearMonth(date2)).getMonths();
  }

Solution 3

This is the solution I came up with when commenting on Bozho

int handleAllowance(LocalDate today) {

    int allowance = membership.allowance();
    if (allowance == 0) return 0;

    // calculate month difference
    int allowanceMonths = Months.monthsBetween(lastAllowanceUpdate.withDayOfMonth(1), today.withDayOfMonth(1)).getMonths();

    // if update was last month or earlier
    if (allowanceMonths > 0) {

        // ...and if today is on or past update day
        int updateDay = Math.min(allowanceDay, today.dayOfMonth().getMaximumValue());
        if (today.getDayOfMonth() >= updateDay) {

            // give credits (multiply with months in the rare case this process consecutively fails to run for 2 months or more)
            final int totalAllowance = allowance * allowanceMonths;
            giveCredits(totalAllowance);

            // update day
            lastAllowanceUpdate = lastAllowanceUpdate.plusMonths(allowanceMonths);

            // return the allowance given
            return totalAllowance;

        }

    }

    return 0;
}

Comments

[Bart van Heukelom]

Won't that return 0 if date1 is January 31 and date2 is February 1? I basically need to discard day information and then calculate the difference...oh, wait, that's how I could do it. :p

[Bart van Heukelom]

I posted my solution as answer

[zeddarn]

I used this and gets this org.joda.time.IllegalFieldValueException: Value 0 for dayOfMonth must be in the range [1,28]

[Matt Leonowicz]

@zeddarn Yes. In Yoda Time months start from 1 (days also), as opposed to Calendar 0. Remember to add +1 if you pass from Calendar to Yoda

[Lucas Oliveira]

This solution works for scenarios like "29/01/2016" and "01/02/2016"!