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   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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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
   *
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   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions are met:
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   *    this list of conditions and the following disclaimer.
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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;
  
  // Android-changed: removed ValueBased paragraph.
  
  /**
   * 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.
   *
   * @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);
      }
  
  }
  