/*

 * Copyright (c) 1996, 2019, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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/*

 * (C) Copyright Taligent, Inc. 1996-1998 - All Rights Reserved

 * (C) Copyright IBM Corp. 1996-1998 - All Rights Reserved

 *

 *   The original version of this source code and documentation is copyrighted

 * and owned by Taligent, Inc., a wholly-owned subsidiary of IBM. These

 * materials are provided under terms of a License Agreement between Taligent

 * and Sun. This technology is protected by multiple US and International

 * patents. This notice and attribution to Taligent may not be removed.

 *   Taligent is a registered trademark of Taligent, Inc.

 *

 */

package java.util;

import java.io.IOException;

import java.io.ObjectInputStream;

import java.time.Instant;

import java.time.ZonedDateTime;

import java.time.temporal.ChronoField;

import sun.util.calendar.BaseCalendar;

import sun.util.calendar.CalendarDate;

import sun.util.calendar.CalendarSystem;

import sun.util.calendar.CalendarUtils;

import sun.util.calendar.Era;

import sun.util.calendar.Gregorian;

import sun.util.calendar.JulianCalendar;

import sun.util.calendar.ZoneInfo;

/**

 * {@code GregorianCalendar} is a concrete subclass of

 * {@code Calendar} and provides the standard calendar system

 * used by most of the world.

 *

 * <p> {@code GregorianCalendar} is a hybrid calendar that

 * supports both the Julian and Gregorian calendar systems with the

 * support of a single discontinuity, which corresponds by default to

 * the Gregorian date when the Gregorian calendar was instituted

 * (October 15, 1582 in some countries, later in others).  The cutover

 * date may be changed by the caller by calling {@link

 * #setGregorianChange(Date) setGregorianChange()}.

 *

 * <p>

 * Historically, in those countries which adopted the Gregorian calendar first,

 * October 4, 1582 (Julian) was thus followed by October 15, 1582 (Gregorian). This calendar models

 * this correctly.  Before the Gregorian cutover, {@code GregorianCalendar}

 * implements the Julian calendar.  The only difference between the Gregorian

 * and the Julian calendar is the leap year rule. The Julian calendar specifies

 * leap years every four years, whereas the Gregorian calendar omits century

 * years which are not divisible by 400.

 *

 * <p>

 * {@code GregorianCalendar} implements <em>proleptic</em> Gregorian and

 * Julian calendars. That is, dates are computed by extrapolating the current

 * rules indefinitely far backward and forward in time. As a result,

 * {@code GregorianCalendar} may be used for all years to generate

 * meaningful and consistent results. However, dates obtained using

 * {@code GregorianCalendar} are historically accurate only from March 1, 4

 * AD onward, when modern Julian calendar rules were adopted.  Before this date,

 * leap year rules were applied irregularly, and before 45 BC the Julian

 * calendar did not even exist.

 *

 * <p>

 * Prior to the institution of the Gregorian calendar, New Year's Day was

 * March 25. To avoid confusion, this calendar always uses January 1. A manual

 * adjustment may be made if desired for dates that are prior to the Gregorian

 * changeover and which fall between January 1 and March 24.

 *

 * <h2><a id="week_and_year">Week Of Year and Week Year</a></h2>

 *

 * <p>Values calculated for the {@link Calendar#WEEK_OF_YEAR

 * WEEK_OF_YEAR} field range from 1 to 53. The first week of a

 * calendar year is the earliest seven day period starting on {@link

 * Calendar#getFirstDayOfWeek() getFirstDayOfWeek()} that contains at

 * least {@link Calendar#getMinimalDaysInFirstWeek()

 * getMinimalDaysInFirstWeek()} days from that year. It thus depends

 * on the values of {@code getMinimalDaysInFirstWeek()}, {@code

 * getFirstDayOfWeek()}, and the day of the week of January 1. Weeks

 * between week 1 of one year and week 1 of the following year

 * (exclusive) are numbered sequentially from 2 to 52 or 53 (except

 * for year(s) involved in the Julian-Gregorian transition).

 *

 * <p>The {@code getFirstDayOfWeek()} and {@code

 * getMinimalDaysInFirstWeek()} values are initialized using

 * locale-dependent resources when constructing a {@code

 * GregorianCalendar}. <a id="iso8601_compatible_setting">The week

 * determination is compatible</a> with the ISO 8601 standard when {@code

 * getFirstDayOfWeek()} is {@code MONDAY} and {@code

 * getMinimalDaysInFirstWeek()} is 4, which values are used in locales

 * where the standard is preferred. These values can explicitly be set by

 * calling {@link Calendar#setFirstDayOfWeek(int) setFirstDayOfWeek()} and

 * {@link Calendar#setMinimalDaysInFirstWeek(int)

 * setMinimalDaysInFirstWeek()}.

 *

 * <p>A <a id="week_year"><em>week year</em></a> is in sync with a

 * {@code WEEK_OF_YEAR} cycle. All weeks between the first and last

 * weeks (inclusive) have the same <em>week year</em> value.

 * Therefore, the first and last days of a week year may have

 * different calendar year values.

 *

 * <p>For example, January 1, 1998 is a Thursday. If {@code

 * getFirstDayOfWeek()} is {@code MONDAY} and {@code

 * getMinimalDaysInFirstWeek()} is 4 (ISO 8601 standard compatible

 * setting), then week 1 of 1998 starts on December 29, 1997, and ends

 * on January 4, 1998. The week year is 1998 for the last three days

 * of calendar year 1997. If, however, {@code getFirstDayOfWeek()} is

 * {@code SUNDAY}, then week 1 of 1998 starts on January 4, 1998, and

 * ends on January 10, 1998; the first three days of 1998 then are

 * part of week 53 of 1997 and their week year is 1997.

 *

 * <h3>Week Of Month</h3>

 *

 * <p>Values calculated for the {@code WEEK_OF_MONTH} field range from 0

 * to 6.  Week 1 of a month (the days with <code>WEEK_OF_MONTH =

 * 1</code>) is the earliest set of at least

 * {@code getMinimalDaysInFirstWeek()} contiguous days in that month,

 * ending on the day before {@code getFirstDayOfWeek()}.  Unlike

 * week 1 of a year, week 1 of a month may be shorter than 7 days, need

 * not start on {@code getFirstDayOfWeek()}, and will not include days of

 * the previous month.  Days of a month before week 1 have a

 * {@code WEEK_OF_MONTH} of 0.

 *

 * <p>For example, if {@code getFirstDayOfWeek()} is {@code SUNDAY}

 * and {@code getMinimalDaysInFirstWeek()} is 4, then the first week of

 * January 1998 is Sunday, January 4 through Saturday, January 10.  These days

 * have a {@code WEEK_OF_MONTH} of 1.  Thursday, January 1 through

 * Saturday, January 3 have a {@code WEEK_OF_MONTH} of 0.  If

 * {@code getMinimalDaysInFirstWeek()} is changed to 3, then January 1

 * through January 3 have a {@code WEEK_OF_MONTH} of 1.

 *

 * <h3>Default Fields Values</h3>

 *

 * <p>The {@code clear} method sets calendar field(s)

 * undefined. {@code GregorianCalendar} uses the following

 * default value for each calendar field if its value is undefined.

 *

 * <table class="striped" style="text-align: left; width: 66%;">

 * <caption style="display:none">GregorianCalendar default field values</caption>

 *   <thead>

 *     <tr>

 *       <th scope="col">

 *          Field

 *       </th>

 *       <th scope="col">

            Default Value

 *       </th>

 *     </tr>

 *   </thead>

 *   <tbody>

 *     <tr>

 *       <th scope="row">

 *              {@code ERA}

 *       </th>

 *       <td>

 *              {@code AD}

 *       </td>

 *     </tr>

 *     <tr>

 *       <th scope="row">

 *              {@code YEAR}

 *       </th>

 *       <td>

 *              {@code 1970}

 *       </td>

 *     </tr>

 *     <tr>

 *       <th scope="row">

 *              {@code MONTH}

 *       </th>

 *       <td>

 *              {@code JANUARY}

 *       </td>

 *     </tr>

 *     <tr>

 *       <th scope="row">

 *              {@code DAY_OF_MONTH}

 *       </th>

 *       <td>

 *              {@code 1}

 *       </td>

 *     </tr>

 *     <tr>

 *       <th scope="row">

 *              {@code DAY_OF_WEEK}

 *       </th>

 *       <td>

 *              {@code the first day of week}

 *       </td>

 *     </tr>

 *     <tr>

 *       <th scope="row">

 *              {@code WEEK_OF_MONTH}

 *       </th>

 *       <td>

 *              {@code 0}

 *       </td>

 *     </tr>

 *     <tr>

 *       <th scope="row">

 *              {@code DAY_OF_WEEK_IN_MONTH}

 *       </th>

 *       <td>

 *              {@code 1}

 *       </td>

 *     </tr>

 *     <tr>

 *       <th scope="row">

 *              {@code AM_PM}

 *       </th>

 *       <td>

 *              {@code AM}

 *       </td>

 *     </tr>

 *     <tr>

 *       <th scope="row">

 *              {@code HOUR, HOUR_OF_DAY, MINUTE, SECOND, MILLISECOND}

 *       </th>

 *       <td>

 *              {@code 0}

 *       </td>

 *     </tr>

 *   </tbody>

 * </table>

 * <br>Default values are not applicable for the fields not listed above.

 *

 * <p>

 * <strong>Example:</strong>

 * <blockquote>

 * <pre>

 * // get the supported ids for GMT-08:00 (Pacific Standard Time)

 * String[] ids = TimeZone.getAvailableIDs(-8 * 60 * 60 * 1000);

 * // if no ids were returned, something is wrong. get out.

 * if (ids.length == 0)

 *     System.exit(0);

 *

 *  // begin output

 * System.out.println("Current Time");

 *

 * // create a Pacific Standard Time time zone

 * SimpleTimeZone pdt = new SimpleTimeZone(-8 * 60 * 60 * 1000, ids[0]);

 *

 * // set up rules for Daylight Saving Time

 * pdt.setStartRule(Calendar.APRIL, 1, Calendar.SUNDAY, 2 * 60 * 60 * 1000);

 * pdt.setEndRule(Calendar.OCTOBER, -1, Calendar.SUNDAY, 2 * 60 * 60 * 1000);

 *

 * // create a GregorianCalendar with the Pacific Daylight time zone

 * // and the current date and time

 * Calendar calendar = new GregorianCalendar(pdt);

 * Date trialTime = new Date();

 * calendar.setTime(trialTime);

 *

 * // print out a bunch of interesting things

 * System.out.println("ERA: " + calendar.get(Calendar.ERA));

 * System.out.println("YEAR: " + calendar.get(Calendar.YEAR));

 * System.out.println("MONTH: " + calendar.get(Calendar.MONTH));

 * System.out.println("WEEK_OF_YEAR: " + calendar.get(Calendar.WEEK_OF_YEAR));

 * System.out.println("WEEK_OF_MONTH: " + calendar.get(Calendar.WEEK_OF_MONTH));

 * System.out.println("DATE: " + calendar.get(Calendar.DATE));

 * System.out.println("DAY_OF_MONTH: " + calendar.get(Calendar.DAY_OF_MONTH));

 * System.out.println("DAY_OF_YEAR: " + calendar.get(Calendar.DAY_OF_YEAR));

 * System.out.println("DAY_OF_WEEK: " + calendar.get(Calendar.DAY_OF_WEEK));

 * System.out.println("DAY_OF_WEEK_IN_MONTH: "

 *                    + calendar.get(Calendar.DAY_OF_WEEK_IN_MONTH));

 * System.out.println("AM_PM: " + calendar.get(Calendar.AM_PM));

 * System.out.println("HOUR: " + calendar.get(Calendar.HOUR));

 * System.out.println("HOUR_OF_DAY: " + calendar.get(Calendar.HOUR_OF_DAY));

 * System.out.println("MINUTE: " + calendar.get(Calendar.MINUTE));

 * System.out.println("SECOND: " + calendar.get(Calendar.SECOND));

 * System.out.println("MILLISECOND: " + calendar.get(Calendar.MILLISECOND));

 * System.out.println("ZONE_OFFSET: "

 *                    + (calendar.get(Calendar.ZONE_OFFSET)/(60*60*1000)));

 * System.out.println("DST_OFFSET: "

 *                    + (calendar.get(Calendar.DST_OFFSET)/(60*60*1000)));

 * System.out.println("Current Time, with hour reset to 3");

 * calendar.clear(Calendar.HOUR_OF_DAY); // so doesn't override

 * calendar.set(Calendar.HOUR, 3);

 * System.out.println("ERA: " + calendar.get(Calendar.ERA));

 * System.out.println("YEAR: " + calendar.get(Calendar.YEAR));

 * System.out.println("MONTH: " + calendar.get(Calendar.MONTH));

 * System.out.println("WEEK_OF_YEAR: " + calendar.get(Calendar.WEEK_OF_YEAR));

 * System.out.println("WEEK_OF_MONTH: " + calendar.get(Calendar.WEEK_OF_MONTH));

 * System.out.println("DATE: " + calendar.get(Calendar.DATE));

 * System.out.println("DAY_OF_MONTH: " + calendar.get(Calendar.DAY_OF_MONTH));

 * System.out.println("DAY_OF_YEAR: " + calendar.get(Calendar.DAY_OF_YEAR));

 * System.out.println("DAY_OF_WEEK: " + calendar.get(Calendar.DAY_OF_WEEK));

 * System.out.println("DAY_OF_WEEK_IN_MONTH: "

 *                    + calendar.get(Calendar.DAY_OF_WEEK_IN_MONTH));

 * System.out.println("AM_PM: " + calendar.get(Calendar.AM_PM));

 * System.out.println("HOUR: " + calendar.get(Calendar.HOUR));

 * System.out.println("HOUR_OF_DAY: " + calendar.get(Calendar.HOUR_OF_DAY));

 * System.out.println("MINUTE: " + calendar.get(Calendar.MINUTE));

 * System.out.println("SECOND: " + calendar.get(Calendar.SECOND));

 * System.out.println("MILLISECOND: " + calendar.get(Calendar.MILLISECOND));

 * System.out.println("ZONE_OFFSET: "

 *        + (calendar.get(Calendar.ZONE_OFFSET)/(60*60*1000))); // in hours

 * System.out.println("DST_OFFSET: "

 *        + (calendar.get(Calendar.DST_OFFSET)/(60*60*1000))); // in hours

 * </pre>

 * </blockquote>

 *

 * @see          TimeZone

 * @author David Goldsmith, Mark Davis, Chen-Lieh Huang, Alan Liu

 * @since 1.1

 */

public class GregorianCalendar extends Calendar {

    /*

     * Implementation Notes

     *

     * The epoch is the number of days or milliseconds from some defined

     * starting point. The epoch for java.util.Date is used here; that is,

     * milliseconds from January 1, 1970 (Gregorian), midnight UTC.  Other

     * epochs which are used are January 1, year 1 (Gregorian), which is day 1

     * of the Gregorian calendar, and December 30, year 0 (Gregorian), which is

     * day 1 of the Julian calendar.

     *

     * We implement the proleptic Julian and Gregorian calendars.  This means we

     * implement the modern definition of the calendar even though the

     * historical usage differs.  For example, if the Gregorian change is set

     * to new Date(Long.MIN_VALUE), we have a pure Gregorian calendar which

     * labels dates preceding the invention of the Gregorian calendar in 1582 as

     * if the calendar existed then.

     *

     * Likewise, with the Julian calendar, we assume a consistent

     * 4-year leap year rule, even though the historical pattern of

     * leap years is irregular, being every 3 years from 45 BCE

     * through 9 BCE, then every 4 years from 8 CE onwards, with no

     * leap years in-between.  Thus date computations and functions

     * such as isLeapYear() are not intended to be historically

     * accurate.

     */

//////////////////

// Class Variables

//////////////////

    /**

     * Value of the {@code ERA} field indicating

     * the period before the common era (before Christ), also known as BCE.

     * The sequence of years at the transition from {@code BC} to {@code AD} is

     * ..., 2 BC, 1 BC, 1 AD, 2 AD,...

     *

     * @see #ERA

     */

    public static final int BC = 0;

    /**

     * Value of the {@link #ERA} field indicating

     * the period before the common era, the same value as {@link #BC}.

     *

     * @see #CE

     */

    static final int BCE = 0;

    /**

     * Value of the {@code ERA} field indicating

     * the common era (Anno Domini), also known as CE.

     * The sequence of years at the transition from {@code BC} to {@code AD} is

     * ..., 2 BC, 1 BC, 1 AD, 2 AD,...

     *

     * @see #ERA

     */

    public static final int AD = 1;

    /**

     * Value of the {@link #ERA} field indicating

     * the common era, the same value as {@link #AD}.

     *

     * @see #BCE

     */

    static final int CE = 1;

    private static final int EPOCH_OFFSET   = 719163; // Fixed date of January 1, 1970 (Gregorian)

    private static final int EPOCH_YEAR     = 1970;

    static final int MONTH_LENGTH[]

        = {31,28,31,30,31,30,31,31,30,31,30,31}; // 0-based

    static final int LEAP_MONTH_LENGTH[]

        = {31,29,31,30,31,30,31,31,30,31,30,31}; // 0-based

    // Useful millisecond constants.  Although ONE_DAY and ONE_WEEK can fit

    // into ints, they must be longs in order to prevent arithmetic overflow

    // when performing (bug 4173516).

    private static final int  ONE_SECOND = 1000;

    private static final int  ONE_MINUTE = 60*ONE_SECOND;

    private static final int  ONE_HOUR   = 60*ONE_MINUTE;

    private static final long ONE_DAY    = 24*ONE_HOUR;

    private static final long ONE_WEEK   = 7*ONE_DAY;

    /*

     * <pre>

     *                            Greatest       Least

     * Field name        Minimum   Minimum     Maximum     Maximum

     * ----------        -------   -------     -------     -------

     * ERA                     0         0           1           1

     * YEAR                    1         1   292269054   292278994

     * MONTH                   0         0          11          11

     * WEEK_OF_YEAR            1         1          52*         53

     * WEEK_OF_MONTH           0         0           4*          6

     * DAY_OF_MONTH            1         1          28*         31

     * DAY_OF_YEAR             1         1         365*        366

     * DAY_OF_WEEK             1         1           7           7

     * DAY_OF_WEEK_IN_MONTH    1         1           4*          6

     * AM_PM                   0         0           1           1

     * HOUR                    0         0          11          11

     * HOUR_OF_DAY             0         0          23          23

     * MINUTE                  0         0          59          59

     * SECOND                  0         0          59          59

     * MILLISECOND             0         0         999         999

     * ZONE_OFFSET        -13:00    -13:00       14:00       14:00

     * DST_OFFSET           0:00      0:00        0:20        2:00

     * </pre>

     * *: depends on the Gregorian change date

     */

    static final int MIN_VALUES[] = {

        BCE,            // ERA

        1,              // YEAR

        JANUARY,        // MONTH

        1,              // WEEK_OF_YEAR

        0,              // WEEK_OF_MONTH

        1,              // DAY_OF_MONTH

        1,              // DAY_OF_YEAR

        SUNDAY,         // DAY_OF_WEEK

        1,              // DAY_OF_WEEK_IN_MONTH

        AM,             // AM_PM

        0,              // HOUR

        0,              // HOUR_OF_DAY

        0,              // MINUTE

        0,              // SECOND

        0,              // MILLISECOND

        -13*ONE_HOUR,   // ZONE_OFFSET (UNIX compatibility)

        0               // DST_OFFSET

    };

    static final int LEAST_MAX_VALUES[] = {

        CE,             // ERA

        292269054,      // YEAR

        DECEMBER,       // MONTH

        52,             // WEEK_OF_YEAR

        4,              // WEEK_OF_MONTH

        28,             // DAY_OF_MONTH

        365,            // DAY_OF_YEAR

        SATURDAY,       // DAY_OF_WEEK

        4,              // DAY_OF_WEEK_IN

        PM,             // AM_PM

        11,             // HOUR

        23,             // HOUR_OF_DAY

        59,             // MINUTE

        59,             // SECOND

        999,            // MILLISECOND

        14*ONE_HOUR,    // ZONE_OFFSET

        20*ONE_MINUTE   // DST_OFFSET (historical least maximum)

    };

    static final int MAX_VALUES[] = {

        CE,             // ERA

        292278994,      // YEAR

        DECEMBER,       // MONTH

        53,             // WEEK_OF_YEAR

        6,              // WEEK_OF_MONTH

        31,             // DAY_OF_MONTH

        366,            // DAY_OF_YEAR

        SATURDAY,       // DAY_OF_WEEK

        6,              // DAY_OF_WEEK_IN

        PM,             // AM_PM

        11,             // HOUR

        23,             // HOUR_OF_DAY

        59,             // MINUTE

        59,             // SECOND

        999,            // MILLISECOND

        14*ONE_HOUR,    // ZONE_OFFSET

        2*ONE_HOUR      // DST_OFFSET (double summer time)

    };

    // Proclaim serialization compatibility with JDK 1.1

    @SuppressWarnings("FieldNameHidesFieldInSuperclass")

    @java.io.Serial

    static final long serialVersionUID = -8125100834729963327L;

    // Reference to the sun.util.calendar.Gregorian instance (singleton).

    private static final Gregorian gcal =

                                CalendarSystem.getGregorianCalendar();

    // Reference to the JulianCalendar instance (singleton), set as needed. See

    // getJulianCalendarSystem().

    private static JulianCalendar jcal;

    // JulianCalendar eras. See getJulianCalendarSystem().