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	/*
	* Copyright (c) 2012, 2015, 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
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	* published by the Free Software Foundation. Oracle designates this
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	*
	* This code is distributed in the hope that it will be useful, but WITHOUT
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	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
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	* You should have received a copy of the GNU General Public License version
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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 SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
	* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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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.CENTURIES;
	import static java.time.temporal.ChronoUnit.DECADES;
	import static java.time.temporal.ChronoUnit.ERAS;
	import static java.time.temporal.ChronoUnit.MILLENNIA;
	import static java.time.temporal.ChronoUnit.MONTHS;
	import static java.time.temporal.ChronoUnit.YEARS;

	import java.io.DataInput;
	import java.io.DataOutput;
	import java.io.IOException;
	import java.io.InvalidObjectException;
	import java.io.ObjectInputStream;
	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.TemporalQueries;
	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.
	*
	* <p>
	* This is a <a href="{@docRoot}/java/lang/doc-files/ValueBased.html">value-based</a>
	* class; use of identity-sensitive operations (including reference equality
	* ({@code ==}), identity hash code, or synchronization) on instances of
	* {@code YearMonth} may have unpredictable results and should be avoided.
	* The {@code equals} method should be used for comparisons.
	*
	* @implSpec
	* 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 Clock#systemDefaultZone() system clock} in the default
	* time-zone to obtain the current year-month.
	* <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(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 as a query 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;
	}
	Objects.requireNonNull(temporal, "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 + " of type " + temporal.getClass().getName(), 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},
	* {@link #get(TemporalField) get} and {@link #with(TemporalField, long)}
	* 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);
	}

	/**
	* Checks if the specified unit is supported.
	* <p>
	* This checks if the specified unit can be added to, or subtracted from, this year-month.
	* If false, then calling the {@link #plus(long, TemporalUnit)} and
	* {@link #minus(long, TemporalUnit) minus} methods will throw an exception.
	* <p>
	* If the unit is a {@link ChronoUnit} then the query is implemented here.
	* The supported units are:
	* <ul>
	* <li>{@code MONTHS}
	* <li>{@code YEARS}
	* <li>{@code DECADES}
	* <li>{@code CENTURIES}
	* <li>{@code MILLENNIA}
	* <li>{@code ERAS}
	* </ul>
	* All other {@code ChronoUnit} instances will return false.
	* <p>
	* If the unit is not a {@code ChronoUnit}, then the result of this method
	* is obtained by invoking {@code TemporalUnit.isSupportedBy(Temporal)}
	* passing {@code this} as the argument.
	* Whether the unit is supported is determined by the unit.
	*
	* @param unit the unit to check, null returns false
	* @return true if the unit can be added/subtracted, false if not
	*/
	@Override
	public boolean isSupported(TemporalUnit unit) {
	if (unit instanceof ChronoUnit) {
	return unit == MONTHS \|\| unit == YEARS \|\| unit == DECADES \|\| unit == CENTURIES \|\| unit == MILLENNIA \|\| unit == ERAS;
	}
	return unit != null && unit.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 of 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 of 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);
	}
	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
	*/
	public boolean isValidDay(int dayOfMonth) {
	return dayOfMonth >= 1 && dayOfMonth <= lengthOfMonth();
	}

	/**
	* Returns the length of the month, taking account of the year.
	* <p>
	* This returns the length of the month in days.
	* For example, a date in January would return 31.
	*
	* @return the length of the month in days, from 28 to 31
	*/
	public int lengthOfMonth() {
	return getMonth().length(isLeapYear());
	}

	/**
	* Returns the length of the year.
	* <p>
	* This returns the length of the year in days, either 365 or 366.
	*
	* @return 366 if the year is leap, 365 otherwise
	*/
	public int lengthOfYear() {
	return (isLeapYear() ? 366 : 365);
	}

	//-----------------------------------------------------------------------
	/**
	* Returns an adjusted copy of this year-month.
	* <p>
	* This returns a {@code YearMonth}, based on this one, with the year-month adjusted.
	* The adjustment takes place using the specified adjuster strategy object.
	* Read the documentation of the adjuster to understand what adjustment will be made.
	* <p>
	* A simple adjuster might simply set the one of the fields, such as the year field.
	* A more complex adjuster might set the year-month to the next month that
	* Halley's comet will pass the Earth.
	* <p>
	* The result of this method is obtained by invoking the
	* {@link TemporalAdjuster#adjustInto(Temporal)} method on the
	* specified adjuster passing {@code this} as the argument.
	* <p>
	* This instance is immutable and unaffected by this method call.
	*
	* @param adjuster the adjuster to use, not null
	* @return a {@code YearMonth} based on {@code this} with the adjustment made, not null
	* @throws DateTimeException if the adjustment cannot be made
	* @throws ArithmeticException if numeric overflow occurs
	*/
	@Override
	public YearMonth with(TemporalAdjuster adjuster) {
	return (YearMonth) adjuster.adjustInto(this);
	}

	/**
	* Returns a copy of this year-month with the specified field set to a new value.
	* <p>
	* This returns a {@code YearMonth}, based on this one, with the value
	* for the specified field changed.
	* This can be used to change any supported field, such as the year or month.
	* If it is not possible to set 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 adjustment is implemented here.
	* The supported fields behave as follows:
	* <ul>
	* <li>{@code MONTH_OF_YEAR} -
	* Returns a {@code YearMonth} with the specified month-of-year.
	* The year will be unchanged.
	* <li>{@code PROLEPTIC_MONTH} -
	* Returns a {@code YearMonth} with the specified proleptic-month.
	* This completely replaces the year and month of this object.
	* <li>{@code YEAR_OF_ERA} -
	* Returns a {@code YearMonth} with the specified year-of-era
	* The month and era will be unchanged.
	* <li>{@code YEAR} -
	* Returns a {@code YearMonth} with the specified year.
	* The month will be unchanged.
	* <li>{@code ERA} -
	* Returns a {@code YearMonth} with the specified era.
	* The month and year-of-era will be unchanged.
	* </ul>
	* <p>
	* In all cases, if the new value is outside the valid range of values for the field
	* then a {@code DateTimeException} will be thrown.
	* <p>
	* 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.adjustInto(Temporal, long)}
	* passing {@code this} as the argument. In this case, the field determines
	* whether and how to adjust the instant.
	* <p>
	* This instance is immutable and unaffected by this method call.
	*
	* @param field the field to set in the result, not null
	* @param newValue the new value of the field in the result
	* @return a {@code YearMonth} based on {@code this} with the specified field set, not null
	* @throws DateTimeException if the field cannot be set
	* @throws UnsupportedTemporalTypeException if the field is not supported
	* @throws ArithmeticException if numeric overflow occurs
	*/
	@Override
	public YearMonth with(TemporalField field, long newValue) {
	if (field instanceof ChronoField) {
	ChronoField f = (ChronoField) field;
	f.checkValidValue(newValue);
	switch (f) {
	case MONTH_OF_YEAR: return withMonth((int) newValue);
	case PROLEPTIC_MONTH: return plusMonths(newValue - getProlepticMonth());
	case YEAR_OF_ERA: return withYear((int) (year < 1 ? 1 - newValue : newValue));
	case YEAR: return withYear((int) newValue);
	case ERA: return (getLong(ERA) == newValue ? this : withYear(1 - year));
	}
	throw new UnsupportedTemporalTypeException("Unsupported field: " + field);
	}
	return field.adjustInto(this, newValue);
	}

	//-----------------------------------------------------------------------
	/**
	* Returns a copy of this {@code YearMonth} with the year altered.
	* <p>
	* This instance is immutable and unaffected by this method call.
	*
	* @param year the year to set in the returned year-month, from MIN_YEAR to MAX_YEAR
	* @return a {@code YearMonth} based on this year-month with the requested year, not null
	* @throws DateTimeException if the year value is invalid
	*/
	public YearMonth withYear(int year) {
	YEAR.checkValidValue(year);
	return with(year, month);
	}

	/**
	* Returns a copy of this {@code YearMonth} with the month-of-year altered.
	* <p>
	* This instance is immutable and unaffected by this method call.
	*
	* @param month the month-of-year to set in the returned year-month, from 1 (January) to 12 (December)
	* @return a {@code YearMonth} based on this year-month with the requested month, not null
	* @throws DateTimeException if the month-of-year value is invalid
	*/
	public YearMonth withMonth(int month) {
	MONTH_OF_YEAR.checkValidValue(month);
	return with(year, month);
	}

	//-----------------------------------------------------------------------
	/**
	* Returns a copy of this year-month with the specified amount added.
	* <p>
	* This returns a {@code YearMonth}, based on this one, with the specified amount added.
	* The amount is typically {@link Period} but may be any other type implementing
	* the {@link TemporalAmount} interface.
	* <p>
	* The calculation is delegated to the amount object by calling
	* {@link TemporalAmount#addTo(Temporal)}. The amount implementation is free
	* to implement the addition in any way it wishes, however it typically
	* calls back to {@link #plus(long, TemporalUnit)}. Consult the documentation
	* of the amount implementation to determine if it can be successfully added.
	* <p>
	* This instance is immutable and unaffected by this method call.
	*
	* @param amountToAdd the amount to add, not null
	* @return a {@code YearMonth} based on this year-month with the addition made, not null
	* @throws DateTimeException if the addition cannot be made
	* @throws ArithmeticException if numeric overflow occurs
	*/
	@Override
	public YearMonth plus(TemporalAmount amountToAdd) {
	return (YearMonth) amountToAdd.addTo(this);
	}

	/**
	* Returns a copy of this year-month with the specified amount added.
	* <p>
	* This returns a {@code YearMonth}, based on this one, with the amount
	* in terms of the unit added. If it is not possible to add the amount, because the
	* unit is not supported or for some other reason, an exception is thrown.
	* <p>
	* If the field is a {@link ChronoUnit} then the addition is implemented here.
	* The supported fields behave as follows:
	* <ul>
	* <li>{@code MONTHS} -
	* Returns a {@code YearMonth} with the specified number of months added.
	* This is equivalent to {@link #plusMonths(long)}.
	* <li>{@code YEARS} -
	* Returns a {@code YearMonth} with the specified number of years added.
	* This is equivalent to {@link #plusYears(long)}.
	* <li>{@code DECADES} -
	* Returns a {@code YearMonth} with the specified number of decades added.
	* This is equivalent to calling {@link #plusYears(long)} with the amount
	* multiplied by 10.
	* <li>{@code CENTURIES} -
	* Returns a {@code YearMonth} with the specified number of centuries added.
	* This is equivalent to calling {@link #plusYears(long)} with the amount
	* multiplied by 100.
	* <li>{@code MILLENNIA} -
	* Returns a {@code YearMonth} with the specified number of millennia added.
	* This is equivalent to calling {@link #plusYears(long)} with the amount
	* multiplied by 1,000.
	* <li>{@code ERAS} -
	* Returns a {@code YearMonth} with the specified number of eras added.
	* Only two eras are supported so the amount must be one, zero or minus one.
	* If the amount is non-zero then the year is changed such that the year-of-era
	* is unchanged.
	* </ul>
	* <p>
	* All other {@code ChronoUnit} instances will throw an {@code UnsupportedTemporalTypeException}.
	* <p>
	* If the field is not a {@code ChronoUnit}, then the result of this method
	* is obtained by invoking {@code TemporalUnit.addTo(Temporal, long)}
	* passing {@code this} as the argument. In this case, the unit determines
	* whether and how to perform the addition.
	* <p>
	* This instance is immutable and unaffected by this method call.
	*
	* @param amountToAdd the amount of the unit to add to the result, may be negative
	* @param unit the unit of the amount to add, not null
	* @return a {@code YearMonth} based on this year-month with the specified amount added, not null
	* @throws DateTimeException if the addition cannot be made
	* @throws UnsupportedTemporalTypeException if the unit is not supported
	* @throws ArithmeticException if numeric overflow occurs
	*/
	@Override
	public YearMonth plus(long amountToAdd, TemporalUnit unit) {
	if (unit instanceof ChronoUnit) {
	switch ((ChronoUnit) unit) {
	case MONTHS: return plusMonths(amountToAdd);
	case YEARS: return plusYears(amountToAdd);
	case DECADES: return plusYears(Math.multiplyExact(amountToAdd, 10));
	case CENTURIES: return plusYears(Math.multiplyExact(amountToAdd, 100));
	case MILLENNIA: return plusYears(Math.multiplyExact(amountToAdd, 1000));
	case ERAS: return with(ERA, Math.addExact(getLong(ERA), amountToAdd));
	}
	throw new UnsupportedTemporalTypeException("Unsupported unit: " + unit);
	}
	return unit.addTo(this, amountToAdd);
	}

	/**
	* Returns a copy of this {@code YearMonth} with the specified number of years added.
	* <p>
	* This instance is immutable and unaffected by this method call.
	*
	* @param yearsToAdd the years to add, may be negative
	* @return a {@code YearMonth} based on this year-month with the years added, not null
	* @throws DateTimeException if the result exceeds the supported range
	*/
	public YearMonth plusYears(long yearsToAdd) {
	if (yearsToAdd == 0) {
	return this;
	}
	int newYear = YEAR.checkValidIntValue(year + yearsToAdd); // safe overflow
	return with(newYear, month);
	}

	/**
	* Returns a copy of this {@code YearMonth} with the specified number of months added.
	* <p>
	* This instance is immutable and unaffected by this method call.
	*
	* @param monthsToAdd the months to add, may be negative
	* @return a {@code YearMonth} based on this year-month with the months added, not null
	* @throws DateTimeException if the result exceeds the supported range
	*/
	public YearMonth plusMonths(long monthsToAdd) {
	if (monthsToAdd == 0) {
	return this;
	}
	long monthCount = year * 12L + (month - 1);
	long calcMonths = monthCount + monthsToAdd; // safe overflow
	int newYear = YEAR.checkValidIntValue(Math.floorDiv(calcMonths, 12));
	int newMonth = (int)Math.floorMod(calcMonths, 12) + 1;
	return with(newYear, newMonth);
	}

	//-----------------------------------------------------------------------
	/**
	* Returns a copy of this year-month with the specified amount subtracted.
	* <p>
	* This returns a {@code YearMonth}, based on this one, with the specified amount subtracted.
	* The amount is typically {@link Period} but may be any other type implementing
	* the {@link TemporalAmount} interface.
	* <p>
	* The calculation is delegated to the amount object by calling
	* {@link TemporalAmount#subtractFrom(Temporal)}. The amount implementation is free
	* to implement the subtraction in any way it wishes, however it typically
	* calls back to {@link #minus(long, TemporalUnit)}. Consult the documentation
	* of the amount implementation to determine if it can be successfully subtracted.
	* <p>
	* This instance is immutable and unaffected by this method call.
	*
	* @param amountToSubtract the amount to subtract, not null
	* @return a {@code YearMonth} based on this year-month with the subtraction made, not null
	* @throws DateTimeException if the subtraction cannot be made
	* @throws ArithmeticException if numeric overflow occurs
	*/
	@Override
	public YearMonth minus(TemporalAmount amountToSubtract) {
	return (YearMonth) amountToSubtract.subtractFrom(this);
	}

	/**
	* Returns a copy of this year-month with the specified amount subtracted.
	* <p>
	* This returns a {@code YearMonth}, based on this one, with the amount
	* in terms of the unit subtracted. If it is not possible to subtract the amount,
	* because the unit is not supported or for some other reason, an exception is thrown.
	* <p>
	* This method is equivalent to {@link #plus(long, TemporalUnit)} with the amount negated.
	* See that method for a full description of how addition, and thus subtraction, works.
	* <p>
	* This instance is immutable and unaffected by this method call.
	*
	* @param amountToSubtract the amount of the unit to subtract from the result, may be negative
	* @param unit the unit of the amount to subtract, not null
	* @return a {@code YearMonth} based on this year-month with the specified amount subtracted, not null
	* @throws DateTimeException if the subtraction cannot be made
	* @throws UnsupportedTemporalTypeException if the unit is not supported
	* @throws ArithmeticException if numeric overflow occurs
	*/
	@Override
	public YearMonth minus(long amountToSubtract, TemporalUnit unit) {
	return (amountToSubtract == Long.MIN_VALUE ? plus(Long.MAX_VALUE, unit).plus(1, unit) : plus(-amountToSubtract, unit));
	}

	/**
	* Returns a copy of this {@code YearMonth} with the specified number of years subtracted.
	* <p>
	* This instance is immutable and unaffected by this method call.
	*
	* @param yearsToSubtract the years to subtract, may be negative
	* @return a {@code YearMonth} based on this year-month with the years subtracted, not null
	* @throws DateTimeException if the result exceeds the supported range
	*/
	public YearMonth minusYears(long yearsToSubtract) {
	return (yearsToSubtract == Long.MIN_VALUE ? plusYears(Long.MAX_VALUE).plusYears(1) : plusYears(-yearsToSubtract));
	}

	/**
	* Returns a copy of this {@code YearMonth} with the specified number of months subtracted.
	* <p>
	* This instance is immutable and unaffected by this method call.
	*
	* @param monthsToSubtract the months to subtract, may be negative
	* @return a {@code YearMonth} based on this year-month with the months subtracted, not null
	* @throws DateTimeException if the result exceeds the supported range
	*/
	public YearMonth minusMonths(long monthsToSubtract) {
	return (monthsToSubtract == Long.MIN_VALUE ? plusMonths(Long.MAX_VALUE).plusMonths(1) : plusMonths(-monthsToSubtract));
	}

	//-----------------------------------------------------------------------
	/**
	* Queries this year-month using the specified query.
	* <p>
	* This queries this year-month using the specified query strategy object.
	* The {@code TemporalQuery} object defines the logic to be used to
	* obtain the result. Read the documentation of the query to understand
	* what the result of this method will be.
	* <p>
	* The result of this method is obtained by invoking the
	* {@link TemporalQuery#queryFrom(TemporalAccessor)} method on the
	* specified query passing {@code this} as the argument.
	*
	* @param <R> the type of the result
	* @param query the query to invoke, not null
	* @return the query result, null may be returned (defined by the query)
	* @throws DateTimeException if unable to query (defined by the query)
	* @throws ArithmeticException if numeric overflow occurs (defined by the query)
	*/
	@SuppressWarnings("unchecked")
	@Override
	public <R> R query(TemporalQuery<R> query) {
	if (query == TemporalQueries.chronology()) {
	return (R) IsoChronology.INSTANCE;
	} else if (query == TemporalQueries.precision()) {
	return (R) MONTHS;
	}
	return Temporal.super.query(query);
	}

	/**
	* Adjusts the specified temporal object to have this year-month.
	* <p>
	* This returns a temporal object of the same observable type as the input
	* with the year and month changed to be the same as this.
	* <p>
	* The adjustment is equivalent to using {@link Temporal#with(TemporalField, long)}
	* passing {@link ChronoField#PROLEPTIC_MONTH} as the field.
	* If the specified temporal object does not use the ISO calendar system then
	* a {@code DateTimeException} is thrown.
	* <p>
	* In most cases, it is clearer to reverse the calling pattern by using
	* {@link Temporal#with(TemporalAdjuster)}:
	* <pre>
	* // these two lines are equivalent, but the second approach is recommended
	* temporal = thisYearMonth.adjustInto(temporal);
	* temporal = temporal.with(thisYearMonth);
	* </pre>
	* <p>
	* This instance is immutable and unaffected by this method call.
	*
	* @param temporal the target object to be adjusted, not null
	* @return the adjusted object, not null
	* @throws DateTimeException if unable to make the adjustment
	* @throws ArithmeticException if numeric overflow occurs
	*/
	@Override
	public Temporal adjustInto(Temporal temporal) {
	if (Chronology.from(temporal).equals(IsoChronology.INSTANCE) == false) {
	throw new DateTimeException("Adjustment only supported on ISO date-time");
	}
	return temporal.with(PROLEPTIC_MONTH, getProlepticMonth());
	}

	/**
	* Calculates the amount of time until another year-month in terms of the specified unit.
	* <p>
	* This calculates the amount of time between two {@code YearMonth}
	* objects in terms of a single {@code TemporalUnit}.
	* The start and end points are {@code this} and the specified year-month.
	* The result will be negative if the end is before the start.
	* The {@code Temporal} passed to this method is converted to a
	* {@code YearMonth} using {@link #from(TemporalAccessor)}.
	* For example, the amount in years between two year-months can be calculated
	* using {@code startYearMonth.until(endYearMonth, YEARS)}.
	* <p>
	* The calculation returns a whole number, representing the number of
	* complete units between the two year-months.
	* For example, the amount in decades between 2012-06 and 2032-05
	* will only be one decade as it is one month short of two decades.
	* <p>
	* There are two equivalent ways of using this method.
	* The first is to invoke this method.
	* The second is to use {@link TemporalUnit#between(Temporal, Temporal)}:
	* <pre>
	* // these two lines are equivalent
	* amount = start.until(end, MONTHS);
	* amount = MONTHS.between(start, end);
	* </pre>
	* The choice should be made based on which makes the code more readable.
	* <p>
	* The calculation is implemented in this method for {@link ChronoUnit}.
	* The units {@code MONTHS}, {@code YEARS}, {@code DECADES},
	* {@code CENTURIES}, {@code MILLENNIA} and {@code ERAS} are supported.
	* Other {@code ChronoUnit} values will throw an exception.
	* <p>
	* If the unit is not a {@code ChronoUnit}, then the result of this method
	* is obtained by invoking {@code TemporalUnit.between(Temporal, Temporal)}
	* passing {@code this} as the first argument and the converted input temporal
	* as the second argument.
	* <p>
	* This instance is immutable and unaffected by this method call.
	*
	* @param endExclusive the end date, exclusive, which is converted to a {@code YearMonth}, not null
	* @param unit the unit to measure the amount in, not null
	* @return the amount of time between this year-month and the end year-month
	* @throws DateTimeException if the amount cannot be calculated, or the end
	* temporal cannot be converted to a {@code YearMonth}
	* @throws UnsupportedTemporalTypeException if the unit is not supported
	* @throws ArithmeticException if numeric overflow occurs
	*/
	@Override
	public long until(Temporal endExclusive, TemporalUnit unit) {
	YearMonth end = YearMonth.from(endExclusive);
	if (unit instanceof ChronoUnit) {
	long monthsUntil = end.getProlepticMonth() - getProlepticMonth(); // no overflow
	switch ((ChronoUnit) unit) {
	case MONTHS: return monthsUntil;
	case YEARS: return monthsUntil / 12;
	case DECADES: return monthsUntil / 120;
	case CENTURIES: return monthsUntil / 1200;
	case MILLENNIA: return monthsUntil / 12000;
	case ERAS: return end.getLong(ERA) - getLong(ERA);
	}
	throw new UnsupportedTemporalTypeException("Unsupported unit: " + unit);
	}
	return unit.between(this, end);
	}

	/**
	* Formats this year-month using the specified formatter.
	* <p>
	* This year-month will be passed to the formatter to produce a string.
	*
	* @param formatter the formatter to use, not null
	* @return the formatted year-month string, not null
	* @throws DateTimeException if an error occurs during printing
	*/
	public String format(DateTimeFormatter formatter) {
	Objects.requireNonNull(formatter, "formatter");
	return formatter.format(this);
	}

	//-----------------------------------------------------------------------
	/**
	* Combines this year-month with a day-of-month to create a {@code LocalDate}.
	* <p>
	* This returns a {@code LocalDate} formed from this year-month and the specified day-of-month.
	* <p>
	* The day-of-month value must be valid for the year-month.
	* <p>
	* This method can be used as part of a chain to produce a date:
	* <pre>
	* LocalDate date = year.atMonth(month).atDay(day);
	* </pre>
	*
	* @param dayOfMonth the day-of-month to use, from 1 to 31
	* @return the date formed from this year-month and the specified day, not null
	* @throws DateTimeException if the day is invalid for the year-month
	* @see #isValidDay(int)
	*/
	public LocalDate atDay(int dayOfMonth) {
	return LocalDate.of(year, month, dayOfMonth);
	}

	/**
	* Returns a {@code LocalDate} at the end of the month.
	* <p>
	* This returns a {@code LocalDate} based on this year-month.
	* The day-of-month is set to the last valid day of the month, taking
	* into account leap years.
	* <p>
	* This method can be used as part of a chain to produce a date:
	* <pre>
	* LocalDate date = year.atMonth(month).atEndOfMonth();
	* </pre>
	*
	* @return the last valid date of this year-month, not null
	*/
	public LocalDate atEndOfMonth() {
	return LocalDate.of(year, month, lengthOfMonth());
	}

	//-----------------------------------------------------------------------
	/**
	* Compares this year-month to another year-month.
	* <p>
	* The comparison is based first on the value of the year, then on the value of the month.
	* It is "consistent with equals", as defined by {@link Comparable}.
	*
	* @param other the other year-month to compare to, not null
	* @return the comparator value, negative if less, positive if greater
	*/
	@Override
	public int compareTo(YearMonth other) {
	int cmp = (year - other.year);
	if (cmp == 0) {
	cmp = (month - other.month);
	}
	return cmp;
	}

	/**
	* Checks if this year-month is after the specified year-month.
	*
	* @param other the other year-month to compare to, not null
	* @return true if this is after the specified year-month
	*/
	public boolean isAfter(YearMonth other) {
	return compareTo(other) > 0;
	}

	/**
	* Checks if this year-month is before the specified year-month.
	*
	* @param other the other year-month to compare to, not null
	* @return true if this point is before the specified year-month
	*/
	public boolean isBefore(YearMonth other) {
	return compareTo(other) < 0;
	}

	//-----------------------------------------------------------------------
	/**
	* Checks if this year-month is equal to another year-month.
	* <p>
	* The comparison is based on the time-line position of the year-months.
	*
	* @param obj the object to check, null returns false
	* @return true if this is equal to the other year-month
	*/
	@Override
	public boolean equals(Object obj) {
	if (this == obj) {
	return true;
	}
	if (obj instanceof YearMonth) {
	YearMonth other = (YearMonth) obj;
	return year == other.year && month == other.month;
	}
	return false;
	}

	/**
	* A hash code for this year-month.
	*
	* @return a suitable hash code
	*/
	@Override
	public int hashCode() {
	return year ^ (month << 27);
	}

	//-----------------------------------------------------------------------
	/**
	* Outputs this year-month as a {@code String}, such as {@code 2007-12}.
	* <p>
	* The output will be in the format {@code uuuu-MM}:
	*
	* @return a string representation of this year-month, not null
	*/
	@Override
	public String toString() {
	int absYear = Math.abs(year);
	StringBuilder buf = new StringBuilder(9);
	if (absYear < 1000) {
	if (year < 0) {
	buf.append(year - 10000).deleteCharAt(1);
	} else {
	buf.append(year + 10000).deleteCharAt(0);
	}
	} else {
	buf.append(year);
	}
	return buf.append(month < 10 ? "-0" : "-")
	.append(month)
	.toString();
	}

	//-----------------------------------------------------------------------
	/**
	* Writes the object using a
	* <a href="../../serialized-form.html#java.time.Ser">dedicated serialized form</a>.
	* @serialData
	* <pre>
	* out.writeByte(12); // identifies a YearMonth
	* out.writeInt(year);
	* out.writeByte(month);
	* </pre>
	*
	* @return the instance of {@code Ser}, not null
	*/
	private Object writeReplace() {
	return new Ser(Ser.YEAR_MONTH_TYPE, this);
	}

	/**
	* Defend against malicious streams.
	*
	* @param s the stream to read
	* @throws InvalidObjectException always
	*/
	private void readObject(ObjectInputStream s) throws InvalidObjectException {
	throw new InvalidObjectException("Deserialization via serialization delegate");
	}

	void writeExternal(DataOutput out) throws IOException {
	out.writeInt(year);
	out.writeByte(month);
	}

	static YearMonth readExternal(DataInput in) throws IOException {
	int year = in.readInt();
	byte month = in.readByte();
	return YearMonth.of(year, month);
	}

	}

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