DateComponents.java

  1. /* Copyright 2002-2020 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.text.DecimalFormat;
  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 IRNSS weeks: 1999-08-22. */
  72.     public static final DateComponents IRNSS_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.     /** Serializable UID. */
  105.     private static final long serialVersionUID = -2462694707837970938L;

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

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

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

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

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

  122.     /** Format for years. */
  123.     private static final DecimalFormat FOUR_DIGITS = new DecimalFormat("0000");

  125.     /** Format for months and days. */
  126.     private static final DecimalFormat TWO_DIGITS  = new DecimalFormat("00");

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

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

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

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

  140.     static {
  141.         // this static statement makes sure the reference epoch are initialized
  142.         // once AFTER the various factories have been set up
  143.         JULIAN_EPOCH          = new DateComponents(-4712,  1,  1);
  144.         MODIFIED_JULIAN_EPOCH = new DateComponents(1858, 11, 17);
  145.         FIFTIES_EPOCH         = new DateComponents(1950, 1, 1);
  146.         CCSDS_EPOCH           = new DateComponents(1958, 1, 1);
  147.         GALILEO_EPOCH         = new DateComponents(1999, 8, 22);
  148.         GPS_EPOCH             = new DateComponents(1980, 1, 6);
  149.         QZSS_EPOCH            = new DateComponents(1980, 1, 6);
  150.         IRNSS_EPOCH           = new DateComponents(1999, 8, 22);
  151.         BEIDOU_EPOCH          = new DateComponents(2006, 1, 1);
  152.         GLONASS_EPOCH         = new DateComponents(1996, 1, 1);
  153.         J2000_EPOCH           = new DateComponents(2000, 1, 1);
  154.         JAVA_EPOCH            = new DateComponents(1970, 1, 1);
  155.         MAX_EPOCH             = new DateComponents(Integer.MAX_VALUE);
  156.         MIN_EPOCH             = new DateComponents(Integer.MIN_VALUE);
  157.     }

  159.     /** Year number. */
  160.     private final int year;

  162.     /** Month number. */
  163.     private final int month;

  165.     /** Day number. */
  166.     private final int day;

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

  179.         // very rough range check
  180.         // (just to avoid ArrayOutOfboundException in MonthDayFactory later)
  181.         if ((month < 1) || (month > 12)) {
  182.             throw new OrekitIllegalArgumentException(OrekitMessages.NON_EXISTENT_MONTH, month);
  183.         }

  185.         // start by trusting the parameters
  186.         this.year  = year;
  187.         this.month = month;
  188.         this.day   = day;

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

  193.         // check the parameters for mismatch
  194.         // (i.e. invalid date components, like 29 february on non-leap years)
  195.         if ((year != check.year) || (month != check.month) || (day != check.day)) {
  196.             throw new OrekitIllegalArgumentException(OrekitMessages.NON_EXISTENT_YEAR_MONTH_DAY,
  197.                                                       year, month, day);
  198.         }

  200.     }

  202.     /** Build a date from its components.
  203.      * @param year year number (may be 0 or negative for BC years)
  204.      * @param month month enumerate
  205.      * @param day day number from 1 to 31
  206.      * @exception IllegalArgumentException if inconsistent arguments
  207.      * are given (parameters out of range, february 29 for non-leap years,
  208.      * dates during the gregorian leap in 1582 ...)
  209.      */
  210.     public DateComponents(final int year, final Month month, final int day)
  211.         throws IllegalArgumentException {
  212.         this(year, month.getNumber(), day);
  213.     }

  215.     /** Build a date from a year and day number.
  216.      * @param year year number (may be 0 or negative for BC years)
  217.      * @param dayNumber day number in the year from 1 to 366
  218.      * @exception IllegalArgumentException if dayNumber is out of range
  219.      * with respect to year
  220.      */
  221.     public DateComponents(final int year, final int dayNumber)
  222.         throws IllegalArgumentException {
  223.         this(J2000_EPOCH, new DateComponents(year - 1, 12, 31).getJ2000Day() + dayNumber);
  224.         if (dayNumber != getDayOfYear()) {
  225.             throw new OrekitIllegalArgumentException(OrekitMessages.NON_EXISTENT_DAY_NUMBER_IN_YEAR,
  226.                                                      dayNumber, year);
  227.         }
  228.     }

  230.     /** Build a date from its offset with respect to a {@link #J2000_EPOCH}.
  231.      * @param offset offset with respect to a {@link #J2000_EPOCH}
  232.      * @see #getJ2000Day()
  233.      */
  234.     public DateComponents(final int offset) {

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

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

  258.     }

  260.     /** Build a date from its offset with respect to a reference epoch.
  261.      * <p>This constructor is mainly useful to build a date from a modified
  262.      * julian day (using {@link #MODIFIED_JULIAN_EPOCH}) or a GPS week number
  263.      * (using {@link #GPS_EPOCH}).</p>
  264.      * @param epoch reference epoch
  265.      * @param offset offset with respect to a reference epoch
  266.      * @see #DateComponents(int)
  267.      * @see #getMJD()
  268.      */
  269.     public DateComponents(final DateComponents epoch, final int offset) {
  270.         this(epoch.getJ2000Day() + offset);
  271.     }

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

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

  295.         // check the parameters for invalid date components
  296.         if ((week != d.getCalendarWeek()) || (dayOfWeek != d.getDayOfWeek())) {
  297.             throw new OrekitIllegalArgumentException(OrekitMessages.NON_EXISTENT_WEEK_DATE,
  298.                                                      wYear, week, dayOfWeek);
  299.         }

  301.         return d;

  303.     }

  305.     /** Parse a string in ISO-8601 format to build a date.
  306.      * <p>The supported formats are:
  307.      * <ul>
  308.      *   <li>basic format calendar date: YYYYMMDD</li>
  309.      *   <li>extended format calendar date: YYYY-MM-DD</li>
  310.      *   <li>basic format ordinal date: YYYYDDD</li>
  311.      *   <li>extended format ordinal date: YYYY-DDD</li>
  312.      *   <li>basic format week date: YYYYWwwD</li>
  313.      *   <li>extended format week date: YYYY-Www-D</li>
  314.      * </ul>
  315.      *
  316.      * <p> As shown by the list above, only the complete representations defined in section 4.1
  317.      * of ISO-8601 standard are supported, neither expended representations nor representations
  318.      * with reduced accuracy are supported.
  319.      *
  320.      * <p>
  321.      * Parsing a single integer as a julian day is <em>not</em> supported as it may be ambiguous
  322.      * with either the basic format calendar date or the basic format ordinal date depending
  323.      * on the number of digits.
  324.      * </p>
  325.      * @param string string to parse
  326.      * @return a parsed date
  327.      * @exception IllegalArgumentException if string cannot be parsed
  328.      */
  329.     public static  DateComponents parseDate(final String string) {

  331.         // is the date a calendar date ?
  332.         final Matcher calendarMatcher = CALENDAR_FORMAT.matcher(string);
  333.         if (calendarMatcher.matches()) {
  334.             return new DateComponents(Integer.parseInt(calendarMatcher.group(1)),
  335.                                       Integer.parseInt(calendarMatcher.group(2)),
  336.                                       Integer.parseInt(calendarMatcher.group(3)));
  337.         }

  339.         // is the date an ordinal date ?
  340.         final Matcher ordinalMatcher = ORDINAL_FORMAT.matcher(string);
  341.         if (ordinalMatcher.matches()) {
  342.             return new DateComponents(Integer.parseInt(ordinalMatcher.group(1)),
  343.                                       Integer.parseInt(ordinalMatcher.group(2)));
  344.         }

  346.         // is the date a week date ?
  347.         final Matcher weekMatcher = WEEK_FORMAT.matcher(string);
  348.         if (weekMatcher.matches()) {
  349.             return createFromWeekComponents(Integer.parseInt(weekMatcher.group(1)),
  350.                                             Integer.parseInt(weekMatcher.group(2)),
  351.                                             Integer.parseInt(weekMatcher.group(3)));
  352.         }

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

  356.     }

  358.     /** Get the year number.
  359.      * @return year number (may be 0 or negative for BC years)
  360.      */
  361.     public int getYear() {
  362.         return year;
  363.     }

  365.     /** Get the month.
  366.      * @return month number from 1 to 12
  367.      */
  368.     public int getMonth() {
  369.         return month;
  370.     }

  372.     /** Get the month as an enumerate.
  373.      * @return month as an enumerate
  374.      */
  375.     public Month getMonthEnum() {
  376.         return Month.getMonth(month);
  377.     }

  379.     /** Get the day.
  380.      * @return day number from 1 to 31
  381.      */
  382.     public int getDay() {
  383.         return day;
  384.     }

  386.     /** Get the day number with respect to J2000 epoch.
  387.      * @return day number with respect to J2000 epoch
  388.      */
  389.     public int getJ2000Day() {
  390.         YearFactory yFactory = GREGORIAN_FACTORY;
  391.         if (year < 1583) {
  392.             if (year < 1) {
  393.                 yFactory = PROLEPTIC_JULIAN_FACTORY;
  394.             } else if ((year < 1582) || (month < 10) || ((month < 11) && (day < 5))) {
  395.                 yFactory = JULIAN_FACTORY;
  396.             }
  397.         }
  398.         final MonthDayFactory mdFactory =
  399.             yFactory.isLeap(year) ? LEAP_YEAR_FACTORY : COMMON_YEAR_FACTORY;
  400.         return yFactory.getLastJ2000DayOfYear(year - 1) +
  401.                mdFactory.getDayInYear(month, day);
  402.     }

  404.     /** Get the modified julian day.
  405.      * @return modified julian day
  406.      */
  407.     public int getMJD() {
  408.         return MJD_TO_J2000 + getJ2000Day();
  409.     }

  411.     /** Get the calendar week number.
  412.      * <p>The calendar week number is a number between 1 and 52 or 53 depending
  413.      * on the year. Week 1 is defined by ISO as the one that includes the first
  414.      * Thursday of a year. Week 1 may therefore start the previous year and week
  415.      * 52 or 53 may end in the next year. As an example calendar date 1995-01-01
  416.      * corresponds to week date 1994-W52-7 (i.e. Sunday in the last week of 1994
  417.      * is in fact the first day of year 1995). Another example is calendar date
  418.      * 1996-12-31 which corresponds to week date 1997-W01-2 (i.e. Tuesday in the
  419.      * first week of 1997 is in fact the last day of year 1996).</p>
  420.      * @return calendar week number
  421.      */
  422.     public int getCalendarWeek() {
  423.         final int firstWeekMonday = getFirstWeekMonday(year);
  424.         int daysSincefirstMonday = getJ2000Day() - firstWeekMonday;
  425.         if (daysSincefirstMonday < 0) {
  426.             // we are still in a week from previous year
  427.             daysSincefirstMonday += firstWeekMonday - getFirstWeekMonday(year - 1);
  428.         } else if (daysSincefirstMonday > 363) {
  429.             // up to three days at end of year may belong to first week of next year
  430.             // (by chance, there is no need for a specific check in year 1582 ...)
  431.             final int weekYearLength = getFirstWeekMonday(year + 1) - firstWeekMonday;
  432.             if (daysSincefirstMonday >= weekYearLength) {
  433.                 daysSincefirstMonday -= weekYearLength;
  434.             }
  435.         }
  436.         return 1 + daysSincefirstMonday / 7;
  437.     }

  439.     /** Get the monday of a year first week.
  440.      * @param year year to consider
  441.      * @return day of the monday of the first weak of year
  442.      */
  443.     private static int getFirstWeekMonday(final int year) {
  444.         final int yearFirst = new DateComponents(year, 1, 1).getJ2000Day();
  445.         final int offsetToMonday = 4 - (yearFirst + 2) % 7;
  446.         return yearFirst + offsetToMonday + ((offsetToMonday > 3) ? -7 : 0);
  447.     }

  449.     /** Get the day of week.
  450.      * <p>Day of week is a number between 1 (Monday) and 7 (Sunday).</p>
  451.      * @return day of week
  452.      */
  453.     public int getDayOfWeek() {
  454.         final int dow = (getJ2000Day() + 6) % 7; // result is between -6 and +6
  455.         return (dow < 1) ? (dow + 7) : dow;
  456.     }

  458.     /** Get the day number in year.
  459.      * <p>Day number in year is between 1 (January 1st) and either 365 or
  460.      * 366 inclusive depending on year.</p>
  461.      * @return day number in year
  462.      */
  463.     public int getDayOfYear() {
  464.         return getJ2000Day() - new DateComponents(year - 1, 12, 31).getJ2000Day();
  465.     }

  467.     /** Get a string representation (ISO-8601) of the date.
  468.      * @return string representation of the date.
  469.      */
  470.     public String toString() {
  471.         return new StringBuffer().
  472.                append(FOUR_DIGITS.format(year)).append('-').
  473.                append(TWO_DIGITS.format(month)).append('-').
  474.                append(TWO_DIGITS.format(day)).
  475.                toString();
  476.     }

  478.     /** {@inheritDoc} */
  479.     public int compareTo(final DateComponents other) {
  480.         final int j2000Day = getJ2000Day();
  481.         final int otherJ2000Day = other.getJ2000Day();
  482.         if (j2000Day < otherJ2000Day) {
  483.             return -1;
  484.         } else if (j2000Day > otherJ2000Day) {
  485.             return 1;
  486.         }
  487.         return 0;
  488.     }

  490.     /** {@inheritDoc} */
  491.     public boolean equals(final Object other) {
  492.         try {
  493.             final DateComponents otherDate = (DateComponents) other;
  494.             return (otherDate != null) && (year == otherDate.year) &&
  495.                    (month == otherDate.month) && (day == otherDate.day);
  496.         } catch (ClassCastException cce) {
  497.             return false;
  498.         }
  499.     }

  501.     /** {@inheritDoc} */
  502.     public int hashCode() {
  503.         return (year << 16) ^ (month << 8) ^ day;
  504.     }

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

  509.         /** Get the year number for a given day number with respect to J2000 epoch.
  510.          * @param j2000Day day number with respect to J2000 epoch
  511.          * @return year number
  512.          */
  513.         int getYear(int j2000Day);

  515.         /** Get the day number with respect to J2000 epoch for new year's Eve.
  516.          * @param year year number
  517.          * @return day number with respect to J2000 epoch for new year's Eve
  518.          */
  519.         int getLastJ2000DayOfYear(int year);

  521.         /** Check if a year is a leap or common year.
  522.          * @param year year number
  523.          * @return true if year is a leap year
  524.          */
  525.         boolean isLeap(int year);

  527.     }

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

  532.         /** {@inheritDoc} */
  533.         public int getYear(final int j2000Day) {
  534.             return  (int) -((-4l * j2000Day - 2920488l) / 1461l);
  535.         }

  537.         /** {@inheritDoc} */
  538.         public int getLastJ2000DayOfYear(final int year) {
  539.             return 365 * year + (year + 1) / 4 - 730123;
  540.         }

  542.         /** {@inheritDoc} */
  543.         public boolean isLeap(final int year) {
  544.             return (year % 4) == 0;
  545.         }

  547.     }

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

  552.         /** {@inheritDoc} */
  553.         public int getYear(final int j2000Day) {
  554.             return  (int) ((4l * j2000Day + 2921948l) / 1461l);
  555.         }

  557.         /** {@inheritDoc} */
  558.         public int getLastJ2000DayOfYear(final int year) {
  559.             return 365 * year + year / 4 - 730122;
  560.         }

  562.         /** {@inheritDoc} */
  563.         public boolean isLeap(final int year) {
  564.             return (year % 4) == 0;
  565.         }

  567.     }

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

  572.         /** {@inheritDoc} */
  573.         public int getYear(final int j2000Day) {

  575.             // year estimate
  576.             int year = (int) ((400l * j2000Day + 292194288l) / 146097l);

  578.             // the previous estimate is one unit too high in some rare cases
  579.             // (240 days in the 400 years gregorian cycle, about 0.16%)
  580.             if (j2000Day <= getLastJ2000DayOfYear(year - 1)) {
  581.                 --year;
  582.             }

  584.             // exact year
  585.             return year;

  587.         }

  589.         /** {@inheritDoc} */
  590.         public int getLastJ2000DayOfYear(final int year) {
  591.             return 365 * year + year / 4 - year / 100 + year / 400 - 730120;
  592.         }

  594.         /** {@inheritDoc} */
  595.         public boolean isLeap(final int year) {
  596.             return ((year % 4) == 0) && (((year % 400) == 0) || ((year % 100) != 0));
  597.         }

  599.     }

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

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

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

  617.         /** Get the day number within year for given month and day numbers.
  618.          * @param month month number
  619.          * @param day day number
  620.          * @return day number within year
  621.          */
  622.         int getDayInYear(int month, int day);

  624.     }

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

  629.         /** Months succession definition. */
  630.         private static final int[] PREVIOUS_MONTH_END_DAY = {
  631.             0, 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335
  632.         };

  634.         /** {@inheritDoc} */
  635.         public int getMonth(final int dayInYear) {
  636.             return (dayInYear < 32) ? 1 : (10 * dayInYear + 313) / 306;
  637.         }

  639.         /** {@inheritDoc} */
  640.         public int getDay(final int dayInYear, final int month) {
  641.             return dayInYear - PREVIOUS_MONTH_END_DAY[month];
  642.         }

  644.         /** {@inheritDoc} */
  645.         public int getDayInYear(final int month, final int day) {
  646.             return day + PREVIOUS_MONTH_END_DAY[month];
  647.         }

  649.     }

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

  654.         /** Months succession definition. */
  655.         private static final int[] PREVIOUS_MONTH_END_DAY = {
  656.             0, 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334
  657.         };

  659.         /** {@inheritDoc} */
  660.         public int getMonth(final int dayInYear) {
  661.             return (dayInYear < 32) ? 1 : (10 * dayInYear + 323) / 306;
  662.         }

  664.         /** {@inheritDoc} */
  665.         public int getDay(final int dayInYear, final int month) {
  666.             return dayInYear - PREVIOUS_MONTH_END_DAY[month];
  667.         }

  669.         /** {@inheritDoc} */
  670.         public int getDayInYear(final int month, final int day) {
  671.             return day + PREVIOUS_MONTH_END_DAY[month];
  672.         }

  674.     }

  676. }
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