calculate number of weeks in a given year

Question

I would like to get the number of weeks in any given year. Even though 52 is accepted as a generalised worldwide answer, the calendars for 2015,

Answer 1

This method calculates the number of weeks a ISO year using the Joda time library.

    import org.joda.time.DateTime;
    import org.joda.time.DateTimeZone;

    public static int weeksInYear(int year) {
        return new DateTime(DateTimeZone.forID("America/Los_Angeles"))
            .withWeekyear(year + 1)
            .withWeekOfWeekyear(1)
            .minusWeeks(1)
            .getWeekOfWeekyear();
    }

Answer 2

@Manjula Weerasinge answer actually introduce a bug for 2016. Here's a better solution.

Calendar cal = Calendar.getInstance();
cal.set(Calendar.YEAR, year);
cal.set(Calendar.MONTH, Calendar.JANUARY);
cal.set(Calendar.DAY_OF_MONTH, 1);
GregorianCalendar gregorianCalendar = new GregorianCalendar();

int weekDay = cal.get(Calendar.DAY_OF_WEEK) - 1;
if (gregorianCalendar.isLeapYear(year)){
   if (weekDay == Calendar.THURSDAY || weekDay == Calendar.WEDNESDAY)
      return 53;
   else
      return 52;
} else {
   if (weekDay == Calendar.THURSDAY)
      return 53;
   else
      return 52;
}

Answer 3

For ISO date format, we can calculate number of weeks as follows:

int getNoOfWeeks(int year) {
    Calendar cal = Calendar.getInstance();
    cal.set(Calendar.YEAR, year);
    cal.setMinimalDaysInFirstWeek(4);
    cal.set(Calendar.DAY_OF_WEEK, Calendar.MONDAY);
    return cal.getActualMaximum(Calendar.WEEK_OF_YEAR);
}

So, for year = 2018, it will return 52, for 2019, it will also return 52, but for 2020 it will return 53 as ISO year has 52 or 53 weeks.