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

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

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/*

 * This file is available under and governed by the GNU General Public

 * License version 2 only, as published by the Free Software Foundation.

 * However, the following notice accompanied the original version of this

 * file:

 *

 * Copyright (c) 2007-2012, Stephen Colebourne & Michael Nascimento Santos

 *

 * All rights reserved.

 *

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions are met:

 *

 *  * Redistributions of source code must retain the above copyright notice,

 *    this list of conditions and the following disclaimer.

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 *    this list of conditions and the following disclaimer in the documentation

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 *  * Neither the name of JSR-310 nor the names of its contributors

 *    may be used to endorse or promote products derived from this software

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package java.time;

import static java.time.temporal.ChronoField.ERA;

import static java.time.temporal.ChronoField.MONTH_OF_YEAR;

import static java.time.temporal.ChronoField.PROLEPTIC_MONTH;

import static java.time.temporal.ChronoField.YEAR;

import static java.time.temporal.ChronoField.YEAR_OF_ERA;

import static java.time.temporal.ChronoUnit.MONTHS;

import java.io.DataInput;

import java.io.DataOutput;

import java.io.IOException;

import java.io.InvalidObjectException;

import java.io.ObjectStreamException;

import java.io.Serializable;

import java.time.chrono.Chronology;

import java.time.chrono.IsoChronology;

import java.time.format.DateTimeFormatter;

import java.time.format.DateTimeFormatterBuilder;

import java.time.format.DateTimeParseException;

import java.time.format.SignStyle;

import java.time.temporal.ChronoField;

import java.time.temporal.ChronoUnit;

import java.time.temporal.Temporal;

import java.time.temporal.TemporalAccessor;

import java.time.temporal.TemporalAdjuster;

import java.time.temporal.TemporalAmount;

import java.time.temporal.TemporalField;

import java.time.temporal.TemporalQuery;

import java.time.temporal.TemporalUnit;

import java.time.temporal.UnsupportedTemporalTypeException;

import java.time.temporal.ValueRange;

import java.util.Objects;

/**

 * A year-month in the ISO-8601 calendar system, such as {@code 2007-12}.

 * <p>

 * {@code YearMonth} is an immutable date-time object that represents the combination

 * of a year and month. Any field that can be derived from a year and month, such as

 * quarter-of-year, can be obtained.

 * <p>

 * This class does not store or represent a day, time or time-zone.

 * For example, the value "October 2007" can be stored in a {@code YearMonth}.

 * <p>

 * The ISO-8601 calendar system is the modern civil calendar system used today

 * in most of the world. It is equivalent to the proleptic Gregorian calendar

 * system, in which today's rules for leap years are applied for all time.

 * For most applications written today, the ISO-8601 rules are entirely suitable.

 * However, any application that makes use of historical dates, and requires them

 * to be accurate will find the ISO-8601 approach unsuitable.

 *

 * This class is immutable and thread-safe.

 *

 * @since 1.8

 */

public final class YearMonth

        implements Temporal, TemporalAdjuster, Comparable<YearMonth>, Serializable {

    /**

     * Serialization version.

     */

    private static final long serialVersionUID = 4183400860270640070L;

    /**

     * Parser.

     */

    private static final DateTimeFormatter PARSER = new DateTimeFormatterBuilder()

        .appendValue(YEAR, 4, 10, SignStyle.EXCEEDS_PAD)

        .appendLiteral('-')

        .appendValue(MONTH_OF_YEAR, 2)

        .toFormatter();

    /**

     * The year.

     */

    private final int year;

    /**

     * The month-of-year, not null.

     */

    private final int month;

    //-----------------------------------------------------------------------

    /**

     * Obtains the current year-month from the system clock in the default time-zone.

     * <p>

     * This will query the {@link java.time.Clock#systemDefaultZone() system clock} in the default

     * time-zone to obtain the current year-month.

     * The zone and offset will be set based on the time-zone in the clock.

     * <p>

     * Using this method will prevent the ability to use an alternate clock for testing

     * because the clock is hard-coded.

     *

     * @return the current year-month using the system clock and default time-zone, not null

     */

    public static YearMonth now() {

        return now(Clock.systemDefaultZone());

    }

    /**

     * Obtains the current year-month from the system clock in the specified time-zone.

     * <p>

     * This will query the {@link Clock#system(java.time.ZoneId) system clock} to obtain the current year-month.

     * Specifying the time-zone avoids dependence on the default time-zone.

     * <p>

     * Using this method will prevent the ability to use an alternate clock for testing

     * because the clock is hard-coded.

     *

     * @param zone  the zone ID to use, not null

     * @return the current year-month using the system clock, not null

     */

    public static YearMonth now(ZoneId zone) {

        return now(Clock.system(zone));

    }

    /**

     * Obtains the current year-month from the specified clock.

     * <p>

     * This will query the specified clock to obtain the current year-month.

     * Using this method allows the use of an alternate clock for testing.

     * The alternate clock may be introduced using {@link Clock dependency injection}.

     *

     * @param clock  the clock to use, not null

     * @return the current year-month, not null

     */

    public static YearMonth now(Clock clock) {

        final LocalDate now = LocalDate.now(clock);  // called once

        return YearMonth.of(now.getYear(), now.getMonth());

    }

    //-----------------------------------------------------------------------

    /**

     * Obtains an instance of {@code YearMonth} from a year and month.

     *

     * @param year  the year to represent, from MIN_YEAR to MAX_YEAR

     * @param month  the month-of-year to represent, not null

     * @return the year-month, not null

     * @throws DateTimeException if the year value is invalid

     */

    public static YearMonth of(int year, Month month) {

        Objects.requireNonNull(month, "month");

        return of(year, month.getValue());

    }

    /**

     * Obtains an instance of {@code YearMonth} from a year and month.

     *

     * @param year  the year to represent, from MIN_YEAR to MAX_YEAR

     * @param month  the month-of-year to represent, from 1 (January) to 12 (December)

     * @return the year-month, not null

     * @throws DateTimeException if either field value is invalid

     */

    public static YearMonth of(int year, int month) {

        YEAR.checkValidValue(year);

        MONTH_OF_YEAR.checkValidValue(month);

        return new YearMonth(year, month);

    }

    //-----------------------------------------------------------------------

    /**

     * Obtains an instance of {@code YearMonth} from a temporal object.

     * <p>

     * This obtains a year-month based on the specified temporal.

     * A {@code TemporalAccessor} represents an arbitrary set of date and time information,

     * which this factory converts to an instance of {@code YearMonth}.

     * <p>

     * The conversion extracts the {@link ChronoField#YEAR YEAR} and

     * {@link ChronoField#MONTH_OF_YEAR MONTH_OF_YEAR} fields.

     * The extraction is only permitted if the temporal object has an ISO

     * chronology, or can be converted to a {@code LocalDate}.

     * <p>

     * This method matches the signature of the functional interface {@link TemporalQuery}

     * allowing it to be used in queries via method reference, {@code YearMonth::from}.

     *

     * @param temporal  the temporal object to convert, not null

     * @return the year-month, not null

     * @throws DateTimeException if unable to convert to a {@code YearMonth}

     */

    public static YearMonth from(TemporalAccessor temporal) {

        if (temporal instanceof YearMonth) {

            return (YearMonth) temporal;

        }

        try {

            if (IsoChronology.INSTANCE.equals(Chronology.from(temporal)) == false) {

                temporal = LocalDate.from(temporal);

            }

            return of(temporal.get(YEAR), temporal.get(MONTH_OF_YEAR));

        } catch (DateTimeException ex) {

            throw new DateTimeException("Unable to obtain YearMonth from TemporalAccessor: " + temporal.getClass(), ex);

        }

    }

    //-----------------------------------------------------------------------

    /**

     * Obtains an instance of {@code YearMonth} from a text string such as {@code 2007-12}.

     * <p>

     * The string must represent a valid year-month.

     * The format must be {@code uuuu-MM}.

     * Years outside the range 0000 to 9999 must be prefixed by the plus or minus symbol.

     *

     * @param text  the text to parse such as "2007-12", not null

     * @return the parsed year-month, not null

     * @throws DateTimeParseException if the text cannot be parsed

     */

    public static YearMonth parse(CharSequence text) {

        return parse(text, PARSER);

    }

    /**

     * Obtains an instance of {@code YearMonth} from a text string using a specific formatter.

     * <p>

     * The text is parsed using the formatter, returning a year-month.

     *

     * @param text  the text to parse, not null

     * @param formatter  the formatter to use, not null

     * @return the parsed year-month, not null

     * @throws DateTimeParseException if the text cannot be parsed

     */

    public static YearMonth parse(CharSequence text, DateTimeFormatter formatter) {

        Objects.requireNonNull(formatter, "formatter");

        return formatter.parse(text, YearMonth::from);

    }

    //-----------------------------------------------------------------------

    /**

     * Constructor.

     *

     * @param year  the year to represent, validated from MIN_YEAR to MAX_YEAR

     * @param month  the month-of-year to represent, validated from 1 (January) to 12 (December)

     */

    private YearMonth(int year, int month) {

        this.year = year;

        this.month = month;

    }

    /**

     * Returns a copy of this year-month with the new year and month, checking

     * to see if a new object is in fact required.

     *

     * @param newYear  the year to represent, validated from MIN_YEAR to MAX_YEAR

     * @param newMonth  the month-of-year to represent, validated not null

     * @return the year-month, not null

     */

    private YearMonth with(int newYear, int newMonth) {

        if (year == newYear && month == newMonth) {

            return this;

        }

        return new YearMonth(newYear, newMonth);

    }

    //-----------------------------------------------------------------------

    /**

     * Checks if the specified field is supported.

     * <p>

     * This checks if this year-month can be queried for the specified field.

     * If false, then calling the {@link #range(TemporalField) range} and

     * {@link #get(TemporalField) get} methods will throw an exception.

     * <p>

     * If the field is a {@link ChronoField} then the query is implemented here.

     * The supported fields are:

     * <ul>

     * <li>{@code MONTH_OF_YEAR}

     * <li>{@code PROLEPTIC_MONTH}

     * <li>{@code YEAR_OF_ERA}

     * <li>{@code YEAR}

     * <li>{@code ERA}

     * </ul>

     * All other {@code ChronoField} instances will return false.

     * <p>

     * If the field is not a {@code ChronoField}, then the result of this method

     * is obtained by invoking {@code TemporalField.isSupportedBy(TemporalAccessor)}

     * passing {@code this} as the argument.

     * Whether the field is supported is determined by the field.

     *

     * @param field  the field to check, null returns false

     * @return true if the field is supported on this year-month, false if not

     */

    @Override

    public boolean isSupported(TemporalField field) {

        if (field instanceof ChronoField) {

            return field == YEAR || field == MONTH_OF_YEAR ||

                    field == PROLEPTIC_MONTH || field == YEAR_OF_ERA || field == ERA;

        }

        return field != null && field.isSupportedBy(this);

    }

    /**

     * Gets the range of valid values for the specified field.

     * <p>

     * The range object expresses the minimum and maximum valid values for a field.

     * This year-month is used to enhance the accuracy of the returned range.

     * If it is not possible to return the range, because the field is not supported

     * or for some other reason, an exception is thrown.

     * <p>

     * If the field is a {@link ChronoField} then the query is implemented here.

     * The {@link #isSupported(TemporalField) supported fields} will return

     * appropriate range instances.

     * All other {@code ChronoField} instances will throw an {@code UnsupportedTemporalTypeException}.

     * <p>

     * If the field is not a {@code ChronoField}, then the result of this method

     * is obtained by invoking {@code TemporalField.rangeRefinedBy(TemporalAccessor)}

     * passing {@code this} as the argument.

     * Whether the range can be obtained is determined by the field.

     *

     * @param field  the field to query the range for, not null

     * @return the range of valid values for the field, not null

     * @throws DateTimeException if the range for the field cannot be obtained

     * @throws UnsupportedTemporalTypeException if the field is not supported

     */

    @Override

    public ValueRange range(TemporalField field) {

        if (field == YEAR_OF_ERA) {

            return (getYear() <= 0 ? ValueRange.of(1, Year.MAX_VALUE + 1) : ValueRange.of(1, Year.MAX_VALUE));

        }

        return Temporal.super.range(field);

    }

    /**

     * Gets the value of the specified field from this year-month as an {@code int}.

     * <p>

     * This queries this year-month for the value for the specified field.

     * The returned value will always be within the valid range of values for the field.

     * If it is not possible to return the value, because the field is not supported

     * or for some other reason, an exception is thrown.

     * <p>

     * If the field is a {@link ChronoField} then the query is implemented here.

     * The {@link #isSupported(TemporalField) supported fields} will return valid

     * values based on this year-month, except {@code PROLEPTIC_MONTH} which is too

     * large to fit in an {@code int} and throw a {@code DateTimeException}.

     * All other {@code ChronoField} instances will throw an {@code UnsupportedTemporalTypeException}.

     * <p>

     * If the field is not a {@code ChronoField}, then the result of this method

     * is obtained by invoking {@code TemporalField.getFrom(TemporalAccessor)}

     * passing {@code this} as the argument. Whether the value can be obtained,

     * and what the value represents, is determined by the field.

     *

     * @param field  the field to get, not null

     * @return the value for the field

     * @throws DateTimeException if a value for the field cannot be obtained or

     *         the value is outside the range of valid values for the field

     * @throws UnsupportedTemporalTypeException if the field is not supported or

     *         the range of values exceeds an {@code int}

     * @throws ArithmeticException if numeric overflow occurs

     */

    @Override  // override for Javadoc

    public int get(TemporalField field) {

        return range(field).checkValidIntValue(getLong(field), field);

    }

    /**

     * Gets the value of the specified field from this year-month as a {@code long}.

     * <p>

     * This queries this year-month for the value for the specified field.

     * If it is not possible to return the value, because the field is not supported

     * or for some other reason, an exception is thrown.

     * <p>

     * If the field is a {@link ChronoField} then the query is implemented here.

     * The {@link #isSupported(TemporalField) supported fields} will return valid

     * values based on this year-month.

     * All other {@code ChronoField} instances will throw an {@code UnsupportedTemporalTypeException}.

     * <p>

     * If the field is not a {@code ChronoField}, then the result of this method

     * is obtained by invoking {@code TemporalField.getFrom(TemporalAccessor)}

     * passing {@code this} as the argument. Whether the value can be obtained,

     * and what the value represents, is determined by the field.

     *

     * @param field  the field to get, not null

     * @return the value for the field

     * @throws DateTimeException if a value for the field cannot be obtained

     * @throws UnsupportedTemporalTypeException if the field is not supported

     * @throws ArithmeticException if numeric overflow occurs

     */

    @Override

    public long getLong(TemporalField field) {

        if (field instanceof ChronoField) {

            switch ((ChronoField) field) {

                case MONTH_OF_YEAR: return month;

                case PROLEPTIC_MONTH: return getProlepticMonth();

                case YEAR_OF_ERA: return (year < 1 ? 1 - year : year);

                case YEAR: return year;

                case ERA: return (year < 1 ? 0 : 1);

            }

            throw new UnsupportedTemporalTypeException("Unsupported field: " + field.getName());

        }

        return field.getFrom(this);

    }

    private long getProlepticMonth() {

        return (year * 12L + month - 1);

    }

    //-----------------------------------------------------------------------

    /**

     * Gets the year field.

     * <p>

     * This method returns the primitive {@code int} value for the year.

     * <p>

     * The year returned by this method is proleptic as per {@code get(YEAR)}.

     *

     * @return the year, from MIN_YEAR to MAX_YEAR

     */

    public int getYear() {

        return year;

    }

    /**

     * Gets the month-of-year field from 1 to 12.

     * <p>

     * This method returns the month as an {@code int} from 1 to 12.

     * Application code is frequently clearer if the enum {@link Month}

     * is used by calling {@link #getMonth()}.

     *

     * @return the month-of-year, from 1 to 12

     * @see #getMonth()

     */

    public int getMonthValue() {

        return month;

    }

    /**

     * Gets the month-of-year field using the {@code Month} enum.

     * <p>

     * This method returns the enum {@link Month} for the month.

     * This avoids confusion as to what {@code int} values mean.

     * If you need access to the primitive {@code int} value then the enum

     * provides the {@link Month#getValue() int value}.

     *

     * @return the month-of-year, not null

     * @see #getMonthValue()

     */

    public Month getMonth() {

        return Month.of(month);

    }

    //-----------------------------------------------------------------------

    /**

     * Checks if the year is a leap year, according to the ISO proleptic

     * calendar system rules.

     * <p>

     * This method applies the current rules for leap years across the whole time-line.

     * In general, a year is a leap year if it is divisible by four without

     * remainder. However, years divisible by 100, are not leap years, with

     * the exception of years divisible by 400 which are.

     * <p>

     * For example, 1904 is a leap year it is divisible by 4.

     * 1900 was not a leap year as it is divisible by 100, however 2000 was a

     * leap year as it is divisible by 400.

     * <p>

     * The calculation is proleptic - applying the same rules into the far future and far past.

     * This is historically inaccurate, but is correct for the ISO-8601 standard.

     *

     * @return true if the year is leap, false otherwise

     */

    public boolean isLeapYear() {

        return IsoChronology.INSTANCE.isLeapYear(year);

    }

    /**

     * Checks if the day-of-month is valid for this year-month.

     * <p>

     * This method checks whether this year and month and the input day form

     * a valid date.

     *

     * @param dayOfMonth  the day-of-month to validate, from 1 to 31, invalid value returns false

     * @return true if the day is valid for this year-month