DateComponents.java

  1. /* Copyright 2002-2025 CS GROUP
  2.  * Licensed to CS GROUP (CS) under one or more
  3.  * contributor license agreements.  See the NOTICE file distributed with
  4.  * this work for additional information regarding copyright ownership.
  5.  * CS licenses this file to You under the Apache License, Version 2.0
  6.  * (the "License"); you may not use this file except in compliance with
  7.  * the License.  You may obtain a copy of the License at
  8.  *
  9.  *   http://www.apache.org/licenses/LICENSE-2.0
  10.  *
  11.  * Unless required by applicable law or agreed to in writing, software
  12.  * distributed under the License is distributed on an "AS IS" BASIS,
  13.  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  14.  * See the License for the specific language governing permissions and
  15.  * limitations under the License.
  16.  */
  17. package org.orekit.time;

  19. import java.io.Serializable;
  20. import java.util.Locale;
  21. import java.util.regex.Matcher;
  22. import java.util.regex.Pattern;

  24. import org.orekit.errors.OrekitIllegalArgumentException;
  25. import org.orekit.errors.OrekitMessages;

  27. /** Class representing a date broken up as year, month and day components.
  28.  * <p>This class uses the astronomical convention for calendars,
  29.  * which is also the convention used by <code>java.util.Date</code>:
  30.  * a year zero is present between years -1 and +1, and 10 days are
  31.  * missing in 1582. The calendar used around these special dates are:</p>
  32.  * <ul>
  33.  *   <li>up to 0000-12-31 : proleptic julian calendar</li>
  34.  *   <li>from 0001-01-01 to 1582-10-04: julian calendar</li>
  35.  *   <li>from 1582-10-15: gregorian calendar</li>
  36.  * </ul>
  37.  * <p>Instances of this class are guaranteed to be immutable.</p>
  38.  * @see TimeComponents
  39.  * @see DateTimeComponents
  40.  * @author Luc Maisonobe
  41.  */
  42. public class DateComponents implements Serializable, Comparable<DateComponents> {

  44.     /** Reference epoch for julian dates: -4712-01-01.
  45.      * <p>Both <code>java.util.Date</code> and {@link DateComponents} classes
  46.      * follow the astronomical conventions and consider a year 0 between
  47.      * years -1 and +1, hence this reference date lies in year -4712 and not
  48.      * in year -4713 as can be seen in other documents or programs that obey
  49.      * a different convention (for example the <code>convcal</code> utility).</p>
  50.      */
  51.     public static final DateComponents JULIAN_EPOCH;

  53.     /** Reference epoch for modified julian dates: 1858-11-17. */
  54.     public static final DateComponents MODIFIED_JULIAN_EPOCH;

  56.     /** Reference epoch for 1950 dates: 1950-01-01. */
  57.     public static final DateComponents FIFTIES_EPOCH;

  59.     /** Reference epoch for CCSDS Time Code Format (CCSDS 301.0-B-4): 1958-01-01. */
  60.     public static final DateComponents CCSDS_EPOCH;

  62.     /** Reference epoch for Galileo System Time: 1999-08-22. */
  63.     public static final DateComponents GALILEO_EPOCH;

  65.     /** Reference epoch for GPS weeks: 1980-01-06. */
  66.     public static final DateComponents GPS_EPOCH;

  68.     /** Reference epoch for QZSS weeks: 1980-01-06. */
  69.     public static final DateComponents QZSS_EPOCH;

  71.     /** Reference epoch for NavIC weeks: 1999-08-22. */
  72.     public static final DateComponents NAVIC_EPOCH;

  74.     /** Reference epoch for BeiDou weeks: 2006-01-01. */
  75.     public static final DateComponents BEIDOU_EPOCH;

  77.     /** Reference epoch for GLONASS four-year interval number: 1996-01-01. */
  78.     public static final DateComponents GLONASS_EPOCH;

  80.     /** J2000.0 Reference epoch: 2000-01-01. */
  81.     public static final DateComponents J2000_EPOCH;

  83.     /** Java Reference epoch: 1970-01-01. */
  84.     public static final DateComponents JAVA_EPOCH;

  86.     /** Maximum supported date.
  87.      * <p>
  88.      * This is date 5881610-07-11 which corresponds to {@code Integer.MAX_VALUE}
  89.      * days after {@link #J2000_EPOCH}.
  90.      * </p>
  91.      * @since 9.0
  92.      */
  93.     public static final DateComponents MAX_EPOCH;

  95.     /** Maximum supported date.
  96.      * <p>
  97.      * This is date -5877490-03-03, which corresponds to {@code Integer.MIN_VALUE}
  98.      * days before {@link #J2000_EPOCH}.
  99.      * </p>
  100.      * @since 9.0
  101.      */
  102.     public static final DateComponents MIN_EPOCH;

  104.     /** Offset between julian day epoch and modified julian day epoch. */
  105.     public static final double JD_TO_MJD = 2400000.5;

  107.     /** Serializable UID. */
  108.     private static final long serialVersionUID = -2462694707837970938L;

  110.     /** Factory for proleptic julian calendar (up to 0000-12-31). */
  111.     private static final YearFactory PROLEPTIC_JULIAN_FACTORY = new ProlepticJulianFactory();

  113.     /** Factory for julian calendar (from 0001-01-01 to 1582-10-04). */
  114.     private static final YearFactory JULIAN_FACTORY           = new JulianFactory();

  116.     /** Factory for gregorian calendar (from 1582-10-15). */
  117.     private static final YearFactory GREGORIAN_FACTORY        = new GregorianFactory();

  119.     /** Factory for leap years. */
  120.     private static final MonthDayFactory LEAP_YEAR_FACTORY    = new LeapYearFactory();

  122.     /** Factory for non-leap years. */
  123.     private static final MonthDayFactory COMMON_YEAR_FACTORY  = new CommonYearFactory();

  125.     /** Offset between J2000 epoch and modified julian day epoch. */
  126.     private static final int MJD_TO_J2000 = 51544;


  129.     /** Basic and extended format calendar date. */
  130.     private static final Pattern CALENDAR_FORMAT = Pattern.compile("^(-?\\d\\d\\d\\d)-?(\\d\\d)-?(\\d\\d)$");

  132.     /** Basic and extended format ordinal date. */
  133.     private static final Pattern ORDINAL_FORMAT = Pattern.compile("^(-?\\d\\d\\d\\d)-?(\\d\\d\\d)$");

  135.     /** Basic and extended format week date. */
  136.     private static final Pattern WEEK_FORMAT = Pattern.compile("^(-?\\d\\d\\d\\d)-?W(\\d\\d)-?(\\d)$");

  138.     static {
  139.         // this static statement makes sure the reference epoch are initialized
  140.         // once AFTER the various factories have been set up
  141.         JULIAN_EPOCH          = new DateComponents(-4712,  1,  1);
  142.         MODIFIED_JULIAN_EPOCH = new DateComponents(1858, 11, 17);
  143.         FIFTIES_EPOCH         = new DateComponents(1950, 1, 1);
  144.         CCSDS_EPOCH           = new DateComponents(1958, 1, 1);
  145.         GALILEO_EPOCH         = new DateComponents(1999, 8, 22);
  146.         GPS_EPOCH             = new DateComponents(1980, 1, 6);
  147.         QZSS_EPOCH            = new DateComponents(1980, 1, 6);
  148.         NAVIC_EPOCH           = new DateComponents(1999, 8, 22);
  149.         BEIDOU_EPOCH          = new DateComponents(2006, 1, 1);
  150.         GLONASS_EPOCH         = new DateComponents(1996, 1, 1);
  151.         J2000_EPOCH           = new DateComponents(2000, 1, 1);
  152.         JAVA_EPOCH            = new DateComponents(1970, 1, 1);
  153.         MAX_EPOCH             = new DateComponents(Integer.MAX_VALUE);
  154.         MIN_EPOCH             = new DateComponents(Integer.MIN_VALUE);
  155.     }

  157.     /** Year number. */
  158.     private final int year;

  160.     /** Month number. */
  161.     private final int month;

  163.     /** Day number. */
  164.     private final int day;

  166.     /** Build a date from its components.
  167.      * @param year year number (may be 0 or negative for BC years)
  168.      * @param month month number from 1 to 12
  169.      * @param day day number from 1 to 31
  170.      * @exception IllegalArgumentException if inconsistent arguments
  171.      * are given (parameters out of range, february 29 for non-leap years,
  172.      * dates during the gregorian leap in 1582 ...)
  173.      */
  174.     public DateComponents(final int year, final int month, final int day)
  175.         throws IllegalArgumentException {

  177.         // very rough range check
  178.         // (just to avoid ArrayOutOfboundException in MonthDayFactory later)
  179.         if (month < 1 || month > 12) {
  180.             throw new OrekitIllegalArgumentException(OrekitMessages.NON_EXISTENT_MONTH, month);
  181.         }

  183.         // start by trusting the parameters
  184.         this.year  = year;
  185.         this.month = month;
  186.         this.day   = day;

  188.         // build a check date from the J2000 day
  189.         final DateComponents check = new DateComponents(getJ2000Day());

  191.         // check the parameters for mismatch
  192.         // (i.e. invalid date components, like 29 february on non-leap years)
  193.         if (year != check.year || month != check.month || day != check.day) {
  194.             throw new OrekitIllegalArgumentException(OrekitMessages.NON_EXISTENT_YEAR_MONTH_DAY,
  195.                                                       year, month, day);
  196.         }

  198.     }

  200.     /** Build a date from its components.
  201.      * @param year year number (may be 0 or negative for BC years)
  202.      * @param month month enumerate
  203.      * @param day day number from 1 to 31
  204.      * @exception IllegalArgumentException if inconsistent arguments
  205.      * are given (parameters out of range, february 29 for non-leap years,
  206.      * dates during the gregorian leap in 1582 ...)
  207.      */
  208.     public DateComponents(final int year, final Month month, final int day)
  209.         throws IllegalArgumentException {
  210.         this(year, month.getNumber(), day);
  211.     }

  213.     /** Build a date from a year and day number.
  214.      * @param year year number (may be 0 or negative for BC years)
  215.      * @param dayNumber day number in the year from 1 to 366
  216.      * @exception IllegalArgumentException if dayNumber is out of range
  217.      * with respect to year
  218.      */
  219.     public DateComponents(final int year, final int dayNumber)
  220.         throws IllegalArgumentException {
  221.         this(J2000_EPOCH, new DateComponents(year - 1, 12, 31).getJ2000Day() + dayNumber);
  222.         if (dayNumber != getDayOfYear()) {
  223.             throw new OrekitIllegalArgumentException(OrekitMessages.NON_EXISTENT_DAY_NUMBER_IN_YEAR,
  224.                                                      dayNumber, year);
  225.         }
  226.     }

  228.     /** Build a date from its offset with respect to a {@link #J2000_EPOCH}.
  229.      * @param offset offset with respect to a {@link #J2000_EPOCH}
  230.      * @see #getJ2000Day()
  231.      */
  232.     public DateComponents(final int offset) {

  234.         // we follow the astronomical convention for calendars:
  235.         // we consider a year zero and 10 days are missing in 1582
  236.         // from 1582-10-15: gregorian calendar
  237.         // from 0001-01-01 to 1582-10-04: julian calendar
  238.         // up to 0000-12-31 : proleptic julian calendar
  239.         YearFactory yFactory = GREGORIAN_FACTORY;
  240.         if (offset < -152384) {
  241.             if (offset > -730122) {
  242.                 yFactory = JULIAN_FACTORY;
  243.             } else {
  244.                 yFactory = PROLEPTIC_JULIAN_FACTORY;
  245.             }
  246.         }
  247.         year = yFactory.getYear(offset);
  248.         final int dayInYear = offset - yFactory.getLastJ2000DayOfYear(year - 1);

  250.         // handle month/day according to the year being a common or leap year
  251.         final MonthDayFactory mdFactory =
  252.             yFactory.isLeap(year) ? LEAP_YEAR_FACTORY : COMMON_YEAR_FACTORY;
  253.         month = mdFactory.getMonth(dayInYear);
  254.         day   = mdFactory.getDay(dayInYear, month);

  256.     }

  258.     /** Build a date from its offset with respect to a reference epoch.
  259.      * <p>This constructor is mainly useful to build a date from a modified
  260.      * julian day (using {@link #MODIFIED_JULIAN_EPOCH}) or a GPS week number
  261.      * (using {@link #GPS_EPOCH}).</p>
  262.      * @param epoch reference epoch
  263.      * @param offset offset with respect to a reference epoch
  264.      * @see #DateComponents(int)
  265.      * @see #getMJD()
  266.      */
  267.     public DateComponents(final DateComponents epoch, final int offset) {
  268.         this(epoch.getJ2000Day() + offset);
  269.     }

  271.     /** Build a date from week components.
  272.      * <p>The calendar week number is a number between 1 and 52 or 53 depending
  273.      * on the year. Week 1 is defined by ISO as the one that includes the first
  274.      * Thursday of a year. Week 1 may therefore start the previous year and week
  275.      * 52 or 53 may end in the next year. As an example calendar date 1995-01-01
  276.      * corresponds to week date 1994-W52-7 (i.e. Sunday in the last week of 1994
  277.      * is in fact the first day of year 1995). This date would beAnother example is calendar date
  278.      * 1996-12-31 which corresponds to week date 1997-W01-2 (i.e. Tuesday in the
  279.      * first week of 1997 is in fact the last day of year 1996).</p>
  280.      * @param wYear year associated to week numbering
  281.      * @param week week number in year, from 1 to 52 or 53
  282.      * @param dayOfWeek day of week, from 1 (Monday) to 7 (Sunday)
  283.      * @return a builded date
  284.      * @exception IllegalArgumentException if inconsistent arguments
  285.      * are given (parameters out of range, week 53 on a 52 weeks year ...)
  286.      */
  287.     public static DateComponents createFromWeekComponents(final int wYear, final int week, final int dayOfWeek)
  288.         throws IllegalArgumentException {

  290.         final DateComponents firstWeekMonday = new DateComponents(getFirstWeekMonday(wYear));
  291.         final DateComponents d = new DateComponents(firstWeekMonday, 7 * week + dayOfWeek - 8);

  293.         // check the parameters for invalid date components
  294.         if (week != d.getCalendarWeek() || dayOfWeek != d.getDayOfWeek()) {
  295.             throw new OrekitIllegalArgumentException(OrekitMessages.NON_EXISTENT_WEEK_DATE,
  296.                                                      wYear, week, dayOfWeek);
  297.         }

  299.         return d;

  301.     }

  303.     /** Parse a string in ISO-8601 format to build a date.
  304.      * <p>The supported formats are:
  305.      * <ul>
  306.      *   <li>basic format calendar date: YYYYMMDD</li>
  307.      *   <li>extended format calendar date: YYYY-MM-DD</li>
  308.      *   <li>basic format ordinal date: YYYYDDD</li>
  309.      *   <li>extended format ordinal date: YYYY-DDD</li>
  310.      *   <li>basic format week date: YYYYWwwD</li>
  311.      *   <li>extended format week date: YYYY-Www-D</li>
  312.      * </ul>
  313.      *
  314.      * <p> As shown by the list above, only the complete representations defined in section 4.1
  315.      * of ISO-8601 standard are supported, neither expended representations nor representations
  316.      * with reduced accuracy are supported.
  317.      *
  318.      * <p>
  319.      * Parsing a single integer as a julian day is <em>not</em> supported as it may be ambiguous
  320.      * with either the basic format calendar date or the basic format ordinal date depending
  321.      * on the number of digits.
  322.      * </p>
  323.      * @param string string to parse
  324.      * @return a parsed date
  325.      * @exception IllegalArgumentException if string cannot be parsed
  326.      */
  327.     public static  DateComponents parseDate(final String string) {

  329.         // is the date a calendar date ?
  330.         final Matcher calendarMatcher = CALENDAR_FORMAT.matcher(string);
  331.         if (calendarMatcher.matches()) {
  332.             return new DateComponents(Integer.parseInt(calendarMatcher.group(1)),
  333.                                       Integer.parseInt(calendarMatcher.group(2)),
  334.                                       Integer.parseInt(calendarMatcher.group(3)));
  335.         }

  337.         // is the date an ordinal date ?
  338.         final Matcher ordinalMatcher = ORDINAL_FORMAT.matcher(string);
  339.         if (ordinalMatcher.matches()) {
  340.             return new DateComponents(Integer.parseInt(ordinalMatcher.group(1)),
  341.                                       Integer.parseInt(ordinalMatcher.group(2)));
  342.         }

  344.         // is the date a week date ?
  345.         final Matcher weekMatcher = WEEK_FORMAT.matcher(string);
  346.         if (weekMatcher.matches()) {
  347.             return createFromWeekComponents(Integer.parseInt(weekMatcher.group(1)),
  348.                                             Integer.parseInt(weekMatcher.group(2)),
  349.                                             Integer.parseInt(weekMatcher.group(3)));
  350.         }

  352.         throw new OrekitIllegalArgumentException(OrekitMessages.NON_EXISTENT_DATE, string);

  354.     }

  356.     /** Get the year number.
  357.      * @return year number (may be 0 or negative for BC years)
  358.      */
  359.     public int getYear() {
  360.         return year;
  361.     }

  363.     /** Get the month.
  364.      * @return month number from 1 to 12
  365.      */
  366.     public int getMonth() {
  367.         return month;
  368.     }

  370.     /** Get the month as an enumerate.
  371.      * @return month as an enumerate
  372.      */
  373.     public Month getMonthEnum() {
  374.         return Month.getMonth(month);
  375.     }

  377.     /** Get the day.
  378.      * @return day number from 1 to 31
  379.      */
  380.     public int getDay() {
  381.         return day;
  382.     }

  384.     /** Get the day number with respect to J2000 epoch.
  385.      * @return day number with respect to J2000 epoch
  386.      */
  387.     public int getJ2000Day() {
  388.         YearFactory yFactory = GREGORIAN_FACTORY;
  389.         if (year < 1583) {
  390.             if (year < 1) {
  391.                 yFactory = PROLEPTIC_JULIAN_FACTORY;
  392.             } else if (year < 1582 || month < 10 || month < 11 && day < 5) {
  393.                 yFactory = JULIAN_FACTORY;
  394.             }
  395.         }
  396.         final MonthDayFactory mdFactory =
  397.             yFactory.isLeap(year) ? LEAP_YEAR_FACTORY : COMMON_YEAR_FACTORY;
  398.         return yFactory.getLastJ2000DayOfYear(year - 1) +
  399.                mdFactory.getDayInYear(month, day);
  400.     }

  402.     /** Get the modified julian day.
  403.      * @return modified julian day
  404.      */
  405.     public int getMJD() {
  406.         return MJD_TO_J2000 + getJ2000Day();
  407.     }

  409.     /** Get the calendar week number.
  410.      * <p>The calendar week number is a number between 1 and 52 or 53 depending
  411.      * on the year. Week 1 is defined by ISO as the one that includes the first
  412.      * Thursday of a year. Week 1 may therefore start the previous year and week
  413.      * 52 or 53 may end in the next year. As an example calendar date 1995-01-01
  414.      * corresponds to week date 1994-W52-7 (i.e. Sunday in the last week of 1994
  415.      * is in fact the first day of year 1995). Another example is calendar date
  416.      * 1996-12-31 which corresponds to week date 1997-W01-2 (i.e. Tuesday in the
  417.      * first week of 1997 is in fact the last day of year 1996).</p>
  418.      * @return calendar week number
  419.      */
  420.     public int getCalendarWeek() {
  421.         final int firstWeekMonday = getFirstWeekMonday(year);
  422.         int daysSincefirstMonday = getJ2000Day() - firstWeekMonday;
  423.         if (daysSincefirstMonday < 0) {
  424.             // we are still in a week from previous year
  425.             daysSincefirstMonday += firstWeekMonday - getFirstWeekMonday(year - 1);
  426.         } else if (daysSincefirstMonday > 363) {
  427.             // up to three days at end of year may belong to first week of next year
  428.             // (by chance, there is no need for a specific check in year 1582 ...)
  429.             final int weekYearLength = getFirstWeekMonday(year + 1) - firstWeekMonday;
  430.             if (daysSincefirstMonday >= weekYearLength) {
  431.                 daysSincefirstMonday -= weekYearLength;
  432.             }
  433.         }
  434.         return 1 + daysSincefirstMonday / 7;
  435.     }

  437.     /** Get the monday of a year first week.
  438.      * @param year year to consider
  439.      * @return day of the monday of the first weak of year
  440.      */
  441.     private static int getFirstWeekMonday(final int year) {
  442.         final int yearFirst = new DateComponents(year, 1, 1).getJ2000Day();
  443.         final int offsetToMonday = 4 - (yearFirst + 2) % 7;
  444.         return yearFirst + offsetToMonday + ((offsetToMonday > 3) ? -7 : 0);
  445.     }

  447.     /** Get the day of week.
  448.      * <p>Day of week is a number between 1 (Monday) and 7 (Sunday).</p>
  449.      * @return day of week
  450.      */
  451.     public int getDayOfWeek() {
  452.         final int dow = (getJ2000Day() + 6) % 7; // result is between -6 and +6
  453.         return (dow < 1) ? (dow + 7) : dow;
  454.     }

  456.     /** Get the day number in year.
  457.      * <p>Day number in year is between 1 (January 1st) and either 365 or
  458.      * 366 inclusive depending on year.</p>
  459.      * @return day number in year
  460.      */
  461.     public int getDayOfYear() {
  462.         return getJ2000Day() - new DateComponents(year - 1, 12, 31).getJ2000Day();
  463.     }

  465.     /** Get a string representation (ISO-8601) of the date.
  466.      * @return string representation of the date.
  467.      */
  468.     public String toString() {
  469.         return String.format(Locale.US, "%04d-%02d-%02d", year, month, day);
  470.     }

  472.     /** {@inheritDoc} */
  473.     public int compareTo(final DateComponents other) {
  474.         final int j2000Day = getJ2000Day();
  475.         final int otherJ2000Day = other.getJ2000Day();
  476.         if (j2000Day < otherJ2000Day) {
  477.             return -1;
  478.         } else if (j2000Day > otherJ2000Day) {
  479.             return 1;
  480.         }
  481.         return 0;
  482.     }

  484.     /** {@inheritDoc} */
  485.     public boolean equals(final Object other) {
  486.         try {
  487.             final DateComponents otherDate = (DateComponents) other;
  488.             return otherDate != null && year == otherDate.year &&
  489.                    month == otherDate.month && day == otherDate.day;
  490.         } catch (ClassCastException cce) {
  491.             return false;
  492.         }
  493.     }

  495.     /** {@inheritDoc} */
  496.     public int hashCode() {
  497.         return (year << 16) ^ (month << 8) ^ day;
  498.     }

  500.     /** Interface for dealing with years sequences according to some calendar. */
  501.     private interface YearFactory {

  503.         /** Get the year number for a given day number with respect to J2000 epoch.
  504.          * @param j2000Day day number with respect to J2000 epoch
  505.          * @return year number
  506.          */
  507.         int getYear(int j2000Day);

  509.         /** Get the day number with respect to J2000 epoch for new year's Eve.
  510.          * @param year year number
  511.          * @return day number with respect to J2000 epoch for new year's Eve
  512.          */
  513.         int getLastJ2000DayOfYear(int year);

  515.         /** Check if a year is a leap or common year.
  516.          * @param year year number
  517.          * @return true if year is a leap year
  518.          */
  519.         boolean isLeap(int year);

  521.     }

  523.     /** Class providing a years sequence compliant with the proleptic Julian calendar. */
  524.     private static class ProlepticJulianFactory implements YearFactory {

  526.         /** {@inheritDoc} */
  527.         public int getYear(final int j2000Day) {
  528.             return  (int) -((-4L * j2000Day - 2920488L) / 1461L);
  529.         }

  531.         /** {@inheritDoc} */
  532.         public int getLastJ2000DayOfYear(final int year) {
  533.             return 365 * year + (year + 1) / 4 - 730123;
  534.         }

  536.         /** {@inheritDoc} */
  537.         public boolean isLeap(final int year) {
  538.             return (year % 4) == 0;
  539.         }

  541.     }

  543.     /** Class providing a years sequence compliant with the Julian calendar. */
  544.     private static class JulianFactory implements YearFactory {

  546.         /** {@inheritDoc} */
  547.         public int getYear(final int j2000Day) {
  548.             return  (int) ((4L * j2000Day + 2921948L) / 1461L);
  549.         }

  551.         /** {@inheritDoc} */
  552.         public int getLastJ2000DayOfYear(final int year) {
  553.             return 365 * year + year / 4 - 730122;
  554.         }

  556.         /** {@inheritDoc} */
  557.         public boolean isLeap(final int year) {
  558.             return (year % 4) == 0;
  559.         }

  561.     }

  563.     /** Class providing a years sequence compliant with the Gregorian calendar. */
  564.     private static class GregorianFactory implements YearFactory {

  566.         /** {@inheritDoc} */
  567.         public int getYear(final int j2000Day) {

  569.             // year estimate
  570.             int year = (int) ((400L * j2000Day + 292194288L) / 146097L);

  572.             // the previous estimate is one unit too high in some rare cases
  573.             // (240 days in the 400 years gregorian cycle, about 0.16%)
  574.             if (j2000Day <= getLastJ2000DayOfYear(year - 1)) {
  575.                 --year;
  576.             }

  578.             // exact year
  579.             return year;

  581.         }

  583.         /** {@inheritDoc} */
  584.         public int getLastJ2000DayOfYear(final int year) {
  585.             return 365 * year + year / 4 - year / 100 + year / 400 - 730120;
  586.         }

  588.         /** {@inheritDoc} */
  589.         public boolean isLeap(final int year) {
  590.             return (year % 4) == 0 && ((year % 400) == 0 || (year % 100) != 0);
  591.         }

  593.     }

  595.     /** Interface for dealing with months sequences according to leap/common years. */
  596.     private interface MonthDayFactory {

  598.         /** Get the month number for a given day number within year.
  599.          * @param dayInYear day number within year
  600.          * @return month number
  601.          */
  602.         int getMonth(int dayInYear);

  604.         /** Get the day number for given month and day number within year.
  605.          * @param dayInYear day number within year
  606.          * @param month month number
  607.          * @return day number
  608.          */
  609.         int getDay(int dayInYear, int month);

  611.         /** Get the day number within year for given month and day numbers.
  612.          * @param month month number
  613.          * @param day day number
  614.          * @return day number within year
  615.          */
  616.         int getDayInYear(int month, int day);

  618.     }

  620.     /** Class providing the months sequence for leap years. */
  621.     private static class LeapYearFactory implements MonthDayFactory {

  623.         /** Months succession definition. */
  624.         private static final int[] PREVIOUS_MONTH_END_DAY = {
  625.             0, 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335
  626.         };

  628.         /** {@inheritDoc} */
  629.         public int getMonth(final int dayInYear) {
  630.             return (dayInYear < 32) ? 1 : (10 * dayInYear + 313) / 306;
  631.         }

  633.         /** {@inheritDoc} */
  634.         public int getDay(final int dayInYear, final int month) {
  635.             return dayInYear - PREVIOUS_MONTH_END_DAY[month];
  636.         }

  638.         /** {@inheritDoc} */
  639.         public int getDayInYear(final int month, final int day) {
  640.             return day + PREVIOUS_MONTH_END_DAY[month];
  641.         }

  643.     }

  645.     /** Class providing the months sequence for common years. */
  646.     private static class CommonYearFactory implements MonthDayFactory {

  648.         /** Months succession definition. */
  649.         private static final int[] PREVIOUS_MONTH_END_DAY = {
  650.             0, 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334
  651.         };

  653.         /** {@inheritDoc} */
  654.         public int getMonth(final int dayInYear) {
  655.             return (dayInYear < 32) ? 1 : (10 * dayInYear + 323) / 306;
  656.         }

  658.         /** {@inheritDoc} */
  659.         public int getDay(final int dayInYear, final int month) {
  660.             return dayInYear - PREVIOUS_MONTH_END_DAY[month];
  661.         }

  663.         /** {@inheritDoc} */
  664.         public int getDayInYear(final int month, final int day) {
  665.             return day + PREVIOUS_MONTH_END_DAY[month];
  666.         }

  668.     }

  670. }
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