Julian day of the year in Java

Question

I have seen the \"solution\" at http://www.rgagnon.com/javadetails/java-0506.html, but it doesn\'t work correctly. E.g. yesterday (June 8) should have been 159, but it said

Answer 1

If you're looking for Julian Day as in the day count since 4713 BC, then you can use the following code instead:

private static int daysSince1900(Date date) {
    Calendar c = new GregorianCalendar();
    c.setTime(date);

    int year = c.get(Calendar.YEAR);
    if (year < 1900 || year > 2099) {
        throw new IllegalArgumentException("daysSince1900 - Date must be between 1900 and 2099");
    }
    year -= 1900;
    int month = c.get(Calendar.MONTH) + 1;
    int days = c.get(Calendar.DAY_OF_MONTH);

    if (month < 3) {
        month += 12;
        year--;
    }
    int yearDays = (int) (year * 365.25);
    int monthDays = (int) ((month + 1) * 30.61);

    return (yearDays + monthDays + days - 63);
}

/**
 * Get day count since Monday, January 1, 4713 BC
 * https://en.wikipedia.org/wiki/Julian_day
 * @param date
 * @param time_of_day percentage past midnight, i.e. noon is 0.5
 * @param timezone in hours, i.e. IST (+05:30) is 5.5
 * @return
 */
private static double julianDay(Date date, double time_of_day, double timezone) {
    return daysSince1900(date) + 2415018.5 + time_of_day - timezone / 24;
}

The above code is based on https://stackoverflow.com/a/9593736, and so is limited to dates between 1900 and 2099.