Java calculate days in year, or between two dates

Question

Is there a method in any native Java class to calculate how many days were/will be in a specific year? As in, was it a Leap year (366 days) or a normal year (365 days)?

Answer 1

You can use the TimeUnit class. For your specific needs this should do:

public static int daysBetween(Date a, Date b) {
    final long dMs = a.getTime() - b.getTime();
    return TimeUnit.DAYS.convert(dMs, TimeUnit.MILLISECONDS);
}

Honestly, I don't see where leap years play any role in this calculation, though. Maybe I missed some aspect of your question?

Edit: Stupid me, the leap years magic happens in the Date.getTime(). Anyway, you don't have to deal with it this way.

Answer 2

GregorianCalendar.isLeapYear(int year)

Answer 3

Another way to do it is to ask the Calendar class for the actual maximum days in a given year:

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

int numOfDays = cal.getActualMaximum(Calendar.DAY_OF_YEAR);
System.out.println(numOfDays);

This will return 366 for a bisestile year, 365 for a normal one.

Note, I used getActualMaximum instead of getMaximum, which will always returns 366.