如何在 Java 日历 API 中使用儒略日数?

The following code defines functions that facilitate using either Julian Day Numbers or Modified Julian Day Numbers with the Java Date/Time/Calendar API. The code is based on algorithms published in Jean Meeus's "Astronomical Algorithms", 1st ed., 1991.

public class JulianDay {

    private static final int YEAR = 0;
    private static final int MONTH = 1;
    private static final int DAY = 2;
    private static final int HOURS = 3;
    private static final int MINUTES = 4;
    private static final int SECONDS = 5;
    private static final int MILLIS = 6;

    :
    :

    // Converts a timestamp presented as an array of integers in the following
    // order (from index 0 to 6): year,month,day,hours,minutes,seconds,millis
    // month (1-12), day (1-28 or 29), hours (0-23), min/sec (0-59) to a
    // Modified Julian Day Number.
    // For clarity and simplicity, the input values are assumed to be well-formed;
    // error checking is not implemented in the snippet.

    public static double toMJD(int[] ymd_hms) {

        int y = ymd_hms[YEAR];
        int m = ymd_hms[MONTH];
        double d = (double) ymd_hms[DAY];

        d = d + ((ymd_hms[HOURS] / 24.0) +
                 (ymd_hms[MINUTES] / 1440.0) +
                 (ymd_hms[SECONDS] / 86400.0) +
                 (ymd_hms[MILLIS] / 86400000.0));

        if (m == 1 || m == 2) {
            y--;
            m = m + 12;
        }

        double a = Math.floor(y / 100);
        double b = 2 - a + Math.floor(a / 4);

        return (Math.floor(365.25 * (y + 4716.0)) +
               Math.floor(30.6001 * (m + 1)) +
               d + b - 1524.5) - 2400000.5;  // for Julian Day omit the 2400000.5 term
    }

    // Converts an Modified Julian Day Number (double) to an integer array representing
    // a timestamp (year,month,day,hours,mins,secs,millis). Works for all positive JDN

    public static int[] toTimestamp(double mjd) {

        int ymd_hms[] = { -1, -1, -1, -1, -1, -1, -1 };
        int a, b, c, d, e, z;

        double jd = mjd + 2400000.5 + 0.5;  // if a JDN is passed as argument,
                                            // omit the 2400000.5 term
        double f, x;

        z = (int) Math.floor(jd);
        f = jd - z;

        if (z >= 2299161) {
            int alpha = (int) Math.floor((z - 1867216.25) / 36524.25);
            a = z + 1 + alpha - (int) Math.floor(alpha / 4);
        } else {
            a = z;
        }

        b = a + 1524;
        c = (int) Math.floor((b - 122.1) / 365.25);
        d = (int) Math.floor(365.25 * c);
        e = (int) Math.floor((b - d) / 30.6001);

        ymd_hms[DAY] = b - d - (int) Math.floor(30.6001 * e);
        ymd_hms[MONTH] = (e < 14)
                ? (e - 1)
                : (e - 13);
        ymd_hms[YEAR] = (ymd_hms[MONTH] > 2)
                ? (c - 4716)
                : (c - 4715);

        for (int i = HOURS; i <= MILLIS; i++) {
            switch(i) {
                case HOURS:
                    f = f * 24.0;
                    break;
                case MINUTES: case SECONDS:
                    f = f * 60.0;
                    break;
                case MILLIS:
                    f = f * 1000.0;
                    break;  
            }
            x = Math.floor(f);
            ymd_hms[i] = (int) x;
            f = f - x;
        }   

        return ymd_hms;
    }
}

这里也提供了这个答案:如何在 Java 日期和儒略日数之间进行转换?.在当前帖子中，提供了该算法的参考资料以及更多讨论.上述算法的实现也不包含 Java API 依赖项(除了数学函数).

JulianDateStamp julianStamp = new JulianDateStamp(julianDays);
JDateTime jdate = new JDateTime(julianStamp);
Date date = new Date(jdate.getTimeInMillis());