calculate number of weeks in a given year

According to the wikipedia article on ISO week date format, You can calculate it using following code.

    Calendar cal = Calendar.getInstance();
    cal.set(Calendar.YEAR, 2015);
    cal.set(Calendar.MONTH, Calendar.DECEMBER);
    cal.set(Calendar.DAY_OF_MONTH, 31);

    int ordinalDay = cal.get(Calendar.DAY_OF_YEAR);
    int weekDay = cal.get(Calendar.DAY_OF_WEEK) - 1; // Sunday = 0
    int numberOfWeeks = (ordinalDay - weekDay + 10) / 7;
    System.out.println(numberOfWeeks);

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Update:

Seems the answer from @Samuel https://stackoverflow.com/a/40174287/201986 is better and free from the bug mentioned by Luca

Quick one liner:

Integer weeksOfYear = Calendar.getInstance().getActualMaximum(Calendar.WEEK_OF_YEAR);