java/11 : java.base/java/time/Year.java

Year
https://openjdk.java.net/
GPLv2 + Classpath Exception
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 * However, the following notice accompanied the original version of this
 * file:
 *
 * Copyright (c) 2007-2012, Stephen Colebourne & Michael Nascimento Santos
 *
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package java.time;

import static java.time.temporal.ChronoField.ERA;
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.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 in the ISO-8601 calendar system, such as 2007.  Year is an immutable date-time object that represents a year. Any field that can be derived from a year can be obtained. 

Note that years in the ISO chronology only align with years in the
Gregorian-Julian system for modern years. Parts of Russia did not switch to the
modern Gregorian/ISO rules until 1920.
As such, historical years must be treated with caution.
 This class does not store or represent a month, day, time or time-zone. For example, the value "2007" can be stored in a Year. 

Years represented by this class follow the ISO-8601 standard and use
the proleptic numbering system. Year 1 is preceded by year 0, then by year -1.

The ISO-8601 calendar system is the modern civil calendar system used today
in most of the world. It is equivalent to the proleptic Gregorian calendar
system, in which today's rules for leap years are applied for all time.
For most applications written today, the ISO-8601 rules are entirely suitable.
However, any application that makes use of historical dates, and requires them
to be accurate will find the ISO-8601 approach unsuitable.

This is a value-based class; use of identity-sensitive operations (including reference equality (==), identity hash code, or synchronization) on instances of Year may have unpredictable results and should be avoided. The equals method should be used for comparisons. 
Implementation Requirements: 
This class is immutable and thread-safe.
Since: 1.8/**
 * A year in the ISO-8601 calendar system, such as {@code 2007}.
 * <p>
 * {@code Year} is an immutable date-time object that represents a year.
 * Any field that can be derived from a year can be obtained.
 * <p>
 * <b>Note that years in the ISO chronology only align with years in the
 * Gregorian-Julian system for modern years. Parts of Russia did not switch to the
 * modern Gregorian/ISO rules until 1920.
 * As such, historical years must be treated with caution.</b>
 * <p>
 * This class does not store or represent a month, day, time or time-zone.
 * For example, the value "2007" can be stored in a {@code Year}.
 * <p>
 * Years represented by this class follow the ISO-8601 standard and use
 * the proleptic numbering system. Year 1 is preceded by year 0, then by year -1.
 * <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.base/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 Year} 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 Year
        implements Temporal, TemporalAdjuster, Comparable<Year>, Serializable {

    The minimum supported year, '-999,999,999'.
/**
     * The minimum supported year, '-999,999,999'.
     */
    public static final int MIN_VALUE = -999_999_999;
    The maximum supported year, '+999,999,999'.
/**
     * The maximum supported year, '+999,999,999'.
     */
    public static final int MAX_VALUE = 999_999_999;

    Serialization version.
/**
     * Serialization version.
     */
    private static final long serialVersionUID = -23038383694477807L;
    Parser.
/**
     * Parser.
     */
    private static final DateTimeFormatter PARSER = new DateTimeFormatterBuilder()
        .appendValue(YEAR, 4, 10, SignStyle.EXCEEDS_PAD)
        .toFormatter();

    The year being represented.
/**
     * The year being represented.
     */
    private final int year;

    //-----------------------------------------------------------------------
    Obtains the current year from the system clock in the default time-zone.
 This will query the system clock in the default time-zone to obtain the current year. 

Using this method will prevent the ability to use an alternate clock for testing
because the clock is hard-coded.
Returns: the current year using the system clock and default time-zone, not null/**
     * Obtains the current year 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.
     * <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 using the system clock and default time-zone, not null
     */
    public static Year now() {
        return now(Clock.systemDefaultZone());
    }

    Obtains the current year from the system clock in the specified time-zone.
 This will query the system clock to obtain the current year. Specifying the time-zone avoids dependence on the default time-zone. 

Using this method will prevent the ability to use an alternate clock for testing
because the clock is hard-coded.
Params: zone –  the zone ID to use, not null
Returns: the current year using the system clock, not null/**
     * Obtains the current year 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.
     * 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 using the system clock, not null
     */
    public static Year now(ZoneId zone) {
        return now(Clock.system(zone));
    }

    Obtains the current year from the specified clock.
 This will query the specified clock to obtain the current year. Using this method allows the use of an alternate clock for testing. The alternate clock may be introduced using dependency injection. 
Params: clock –  the clock to use, not null
Returns: the current year, not null/**
     * Obtains the current year from the specified clock.
     * <p>
     * This will query the specified clock to obtain the current year.
     * 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, not null
     */
    public static Year now(Clock clock) {
        final LocalDate now = LocalDate.now(clock);  // called once
        return Year.of(now.getYear());
    }

    //-----------------------------------------------------------------------
    Obtains an instance of Year. 
This method accepts a year value from the proleptic ISO calendar system.

The year 2AD/CE is represented by 2.

The year 1AD/CE is represented by 1.

The year 1BC/BCE is represented by 0.

The year 2BC/BCE is represented by -1.

Params: isoYear –  the ISO proleptic year to represent, from MIN_VALUE to MAX_VALUE
Throws: DateTimeException – if the field is invalid
Returns: the year, not null/**
     * Obtains an instance of {@code Year}.
     * <p>
     * This method accepts a year value from the proleptic ISO calendar system.
     * <p>
     * The year 2AD/CE is represented by 2.<br>
     * The year 1AD/CE is represented by 1.<br>
     * The year 1BC/BCE is represented by 0.<br>
     * The year 2BC/BCE is represented by -1.<br>
     *
     * @param isoYear  the ISO proleptic year to represent, from {@code MIN_VALUE} to {@code MAX_VALUE}
     * @return the year, not null
     * @throws DateTimeException if the field is invalid
     */
    public static Year of(int isoYear) {
        YEAR.checkValidValue(isoYear);
        return new Year(isoYear);
    }

    //-----------------------------------------------------------------------
    Obtains an instance of Year from a temporal object.  This obtains a year based on the specified temporal. A TemporalAccessor represents an arbitrary set of date and time information, which this factory converts to an instance of Year. 
 The conversion extracts the year field. The extraction is only permitted if the temporal object has an ISO chronology, or can be converted to a LocalDate. 
 This method matches the signature of the functional interface TemporalQuery allowing it to be used as a query via method reference, Year::from. 
Params: temporal –  the temporal object to convert, not null
Throws: DateTimeException – if unable to convert to a Year
Returns: the year, not null/**
     * Obtains an instance of {@code Year} from a temporal object.
     * <p>
     * This obtains a year 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 Year}.
     * <p>
     * The conversion extracts the {@link ChronoField#YEAR year} field.
     * 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 Year::from}.
     *
     * @param temporal  the temporal object to convert, not null
     * @return the year, not null
     * @throws DateTimeException if unable to convert to a {@code Year}
     */
    public static Year from(TemporalAccessor temporal) {
        if (temporal instanceof Year) {
            return (Year) temporal;
        }
        Objects.requireNonNull(temporal, "temporal");
        try {
            if (IsoChronology.INSTANCE.equals(Chronology.from(temporal)) == false) {
                temporal = LocalDate.from(temporal);
            }
            return of(temporal.get(YEAR));
        } catch (DateTimeException ex) {
            throw new DateTimeException("Unable to obtain Year from TemporalAccessor: " +
                    temporal + " of type " + temporal.getClass().getName(), ex);
        }
    }

    //-----------------------------------------------------------------------
    Obtains an instance of Year from a text string such as 2007. 
The string must represent a valid year.
Years outside the range 0000 to 9999 must be prefixed by the plus or minus symbol.
Params: text –  the text to parse such as "2007", not null
Throws: DateTimeParseException – if the text cannot be parsed
Returns: the parsed year, not null/**
     * Obtains an instance of {@code Year} from a text string such as {@code 2007}.
     * <p>
     * The string must represent a valid year.
     * 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", not null
     * @return the parsed year, not null
     * @throws DateTimeParseException if the text cannot be parsed
     */
    public static Year parse(CharSequence text) {
        return parse(text, PARSER);
    }

    Obtains an instance of Year from a text string using a specific formatter. 
The text is parsed using the formatter, returning a year.
Params: text –  the text to parse, not null
formatter –  the formatter to use, not null
Throws: DateTimeParseException – if the text cannot be parsed
Returns: the parsed year, not null/**
     * Obtains an instance of {@code Year} from a text string using a specific formatter.
     * <p>
     * The text is parsed using the formatter, returning a year.
     *
     * @param text  the text to parse, not null
     * @param formatter  the formatter to use, not null
     * @return the parsed year, not null
     * @throws DateTimeParseException if the text cannot be parsed
     */
    public static Year parse(CharSequence text, DateTimeFormatter formatter) {
        Objects.requireNonNull(formatter, "formatter");
        return formatter.parse(text, Year::from);
    }

    //-------------------------------------------------------------------------
    Checks if the year is a leap year, according to the ISO proleptic
calendar system rules.

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.

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.

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.
Params: year –  the year to check
Returns: true if the year is leap, false otherwise/**
     * 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.
     *
     * @param year  the year to check
     * @return true if the year is leap, false otherwise
     */
    public static boolean isLeap(long year) {
        return ((year & 3) == 0) && ((year % 100) != 0 || (year % 400) == 0);
    }

    //-----------------------------------------------------------------------
    Constructor.
Params: year –  the year to represent/**
     * Constructor.
     *
     * @param year  the year to represent
     */
    private Year(int year) {
        this.year = year;
    }

    //-----------------------------------------------------------------------
    Gets the year value.
 The year returned by this method is proleptic as per get(YEAR). 
Returns: the year, MIN_VALUE to MAX_VALUE/**
     * Gets the year value.
     * <p>
     * The year returned by this method is proleptic as per {@code get(YEAR)}.
     *
     * @return the year, {@code MIN_VALUE} to {@code MAX_VALUE}
     */
    public int getValue() {
        return year;
    }

    //-----------------------------------------------------------------------
    Checks if the specified field is supported.
 This checks if this year can be queried for the specified field. If false, then calling the range, get and with(TemporalField, long) methods will throw an exception. 
 If the field is a ChronoField then the query is implemented here. The supported fields are: 

YEAR_OF_ERA 
YEAR 
ERA 
 All other ChronoField instances will return false.  If the field is not a ChronoField, then the result of this method is obtained by invoking TemporalField.isSupportedBy(TemporalAccessor) passing this as the argument. Whether the field is supported is determined by the field. 
Params: field –  the field to check, null returns false
Returns: true if the field is supported on this year, false if not/**
     * Checks if the specified field is supported.
     * <p>
     * This checks if this year 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 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, false if not
     */
    @Override
    public boolean isSupported(TemporalField field) {
        if (field instanceof ChronoField) {
            return field == YEAR || field == YEAR_OF_ERA || field == ERA;
        }
        return field != null && field.isSupportedBy(this);
    }

    Checks if the specified unit is supported.
 This checks if the specified unit can be added to, or subtracted from, this year. If false, then calling the plus(long, TemporalUnit) and minus methods will throw an exception. 
 If the unit is a ChronoUnit then the query is implemented here. The supported units are: 

YEARS 
DECADES 
CENTURIES 
MILLENNIA 
ERAS 
 All other ChronoUnit instances will return false.  If the unit is not a ChronoUnit, then the result of this method is obtained by invoking TemporalUnit.isSupportedBy(Temporal) passing this as the argument. Whether the unit is supported is determined by the unit. 
Params: unit –  the unit to check, null returns false
Returns: true if the unit can be added/subtracted, false if not/**
     * Checks if the specified unit is supported.
     * <p>
     * This checks if the specified unit can be added to, or subtracted from, this year.
     * 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 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 == 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.

The range object expresses the minimum and maximum valid values for a field.
This year 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.
 If the field is a ChronoField then the query is implemented here. The supported fields will return appropriate range instances. All other ChronoField instances will throw an UnsupportedTemporalTypeException. 
 If the field is not a ChronoField, then the result of this method is obtained by invoking TemporalField.rangeRefinedBy(TemporalAccessor) passing this as the argument. Whether the range can be obtained is determined by the field. 
Params: field –  the field to query the range for, not null
Throws: DateTimeException – if the range for the field cannot be obtained
UnsupportedTemporalTypeException – if the field is not supported
Returns: the range of valid values for the field, not null/**
     * 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 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 (year <= 0 ? ValueRange.of(1, MAX_VALUE + 1) : ValueRange.of(1, MAX_VALUE));
        }
        return Temporal.super.range(field);
    }

    Gets the value of the specified field from this year as an int. 
This queries this year 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.
 If the field is a ChronoField then the query is implemented here. The supported fields will return valid values based on this year. All other ChronoField instances will throw an UnsupportedTemporalTypeException. 
 If the field is not a ChronoField, then the result of this method is obtained by invoking TemporalField.getFrom(TemporalAccessor) passing this as the argument. Whether the value can be obtained, and what the value represents, is determined by the field. 
Params: field –  the field to get, not null
Throws: DateTimeException – if a value for the field cannot be obtained or
        the value is outside the range of valid values for the field
UnsupportedTemporalTypeException – if the field is not supported or the range of values exceeds an int
ArithmeticException – if numeric overflow occurs
Returns: the value for the field/**
     * Gets the value of the specified field from this year as an {@code int}.
     * <p>
     * This queries this year 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.
     * 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 as a long. 
This queries this year 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.
 If the field is a ChronoField then the query is implemented here. The supported fields will return valid values based on this year. All other ChronoField instances will throw an UnsupportedTemporalTypeException. 
 If the field is not a ChronoField, then the result of this method is obtained by invoking TemporalField.getFrom(TemporalAccessor) passing this as the argument. Whether the value can be obtained, and what the value represents, is determined by the field. 
Params: field –  the field to get, not null
Throws: DateTimeException – if a value for the field cannot be obtained
UnsupportedTemporalTypeException – if the field is not supported
ArithmeticException – if numeric overflow occurs
Returns: the value for the field/**
     * Gets the value of the specified field from this year as a {@code long}.
     * <p>
     * This queries this year 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.
     * 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 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);
    }

    //-----------------------------------------------------------------------
    Checks if the year is a leap year, according to the ISO proleptic
calendar system rules.

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.

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.

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.
Returns: true if the year is leap, false otherwise/**
     * 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 isLeap() {
        return Year.isLeap(year);
    }

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

This method checks whether this year and the input month and day form
a valid date.
Params: monthDay –  the month-day to validate, null returns false
Returns: true if the month and day are valid for this year/**
     * Checks if the month-day is valid for this year.
     * <p>
     * This method checks whether this year and the input month and day form
     * a valid date.
     *
     * @param monthDay  the month-day to validate, null returns false
     * @return true if the month and day are valid for this year
     */
    public boolean isValidMonthDay(MonthDay monthDay) {
        return monthDay != null && monthDay.isValidYear(year);
    }

    Gets the length of this year in days.
Returns: the length of this year in days, 365 or 366/**
     * Gets the length of this year in days.
     *
     * @return the length of this year in days, 365 or 366
     */
    public int length() {
        return isLeap() ? 366 : 365;
    }

    //-----------------------------------------------------------------------
    Returns an adjusted copy of this year.
 This returns a Year, based on this one, with the year adjusted. The adjustment takes place using the specified adjuster strategy object. Read the documentation of the adjuster to understand what adjustment will be made. 
 The result of this method is obtained by invoking the TemporalAdjuster.adjustInto(Temporal) method on the specified adjuster passing this as the argument. 

This instance is immutable and unaffected by this method call.
Params: adjuster – the adjuster to use, not null
Throws: DateTimeException – if the adjustment cannot be made
ArithmeticException – if numeric overflow occurs
Returns: a Year based on this with the adjustment made, not null/**
     * Returns an adjusted copy of this year.
     * <p>
     * This returns a {@code Year}, based on this one, with the year 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>
     * 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 Year} 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 Year with(TemporalAdjuster adjuster) {
        return (Year) adjuster.adjustInto(this);
    }

    Returns a copy of this year with the specified field set to a new value.
 This returns a Year, based on this one, with the value for the specified field changed. If it is not possible to set the value, because the field is not supported or for some other reason, an exception is thrown. 
 If the field is a ChronoField then the adjustment is implemented here. The supported fields behave as follows: 

YEAR_OF_ERA - Returns a Year with the specified year-of-era The era will be unchanged. 
YEAR - Returns a Year with the specified year. This completely replaces the date and is equivalent to of(int). 
ERA - Returns a Year with the specified era. The year-of-era will be unchanged. 
 In all cases, if the new value is outside the valid range of values for the field then a DateTimeException will be thrown. 
 All other ChronoField instances will throw an UnsupportedTemporalTypeException. 
 If the field is not a ChronoField, then the result of this method is obtained by invoking TemporalField.adjustInto(Temporal, long) passing this as the argument. In this case, the field determines whether and how to adjust the instant. 

This instance is immutable and unaffected by this method call.
Params: field –  the field to set in the result, not null
newValue –  the new value of the field in the result
Throws: DateTimeException – if the field cannot be set
UnsupportedTemporalTypeException – if the field is not supported
ArithmeticException – if numeric overflow occurs
Returns: a Year based on this with the specified field set, not null/**
     * Returns a copy of this year with the specified field set to a new value.
     * <p>
     * This returns a {@code Year}, based on this one, with the value
     * for the specified field changed.
     * 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 YEAR_OF_ERA} -
     *  Returns a {@code Year} with the specified year-of-era
     *  The era will be unchanged.
     * <li>{@code YEAR} -
     *  Returns a {@code Year} with the specified year.
     *  This completely replaces the date and is equivalent to {@link #of(int)}.
     * <li>{@code ERA} -
     *  Returns a {@code Year} with the specified era.
     *  The 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 Year} 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 Year with(TemporalField field, long newValue) {
        if (field instanceof ChronoField) {
            ChronoField f = (ChronoField) field;
            f.checkValidValue(newValue);
            switch (f) {
                case YEAR_OF_ERA: return Year.of((int) (year < 1 ? 1 - newValue : newValue));
                case YEAR: return Year.of((int) newValue);
                case ERA: return (getLong(ERA) == newValue ? this : Year.of(1 - year));
            }
            throw new UnsupportedTemporalTypeException("Unsupported field: " + field);
        }
        return field.adjustInto(this, newValue);
    }

    //-----------------------------------------------------------------------
    Returns a copy of this year with the specified amount added.
 This returns a Year, based on this one, with the specified amount added. The amount is typically Period but may be any other type implementing the TemporalAmount interface. 
 The calculation is delegated to the amount object by calling TemporalAmount.addTo(Temporal). The amount implementation is free to implement the addition in any way it wishes, however it typically calls back to plus(long, TemporalUnit). Consult the documentation of the amount implementation to determine if it can be successfully added. 

This instance is immutable and unaffected by this method call.
Params: amountToAdd –  the amount to add, not null
Throws: DateTimeException – if the addition cannot be made
ArithmeticException – if numeric overflow occurs
Returns: a Year based on this year with the addition made, not null/**
     * Returns a copy of this year with the specified amount added.
     * <p>
     * This returns a {@code Year}, 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 Year} based on this year with the addition made, not null
     * @throws DateTimeException if the addition cannot be made
     * @throws ArithmeticException if numeric overflow occurs
     */
    @Override
    public Year plus(TemporalAmount amountToAdd) {
        return (Year) amountToAdd.addTo(this);
    }

    Returns a copy of this year with the specified amount added.
 This returns a Year, 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. 
 If the field is a ChronoUnit then the addition is implemented here. The supported fields behave as follows: 

YEARS - Returns a Year with the specified number of years added. This is equivalent to plusYears(long). 
DECADES - Returns a Year with the specified number of decades added. This is equivalent to calling plusYears(long) with the amount multiplied by 10. 
CENTURIES - Returns a Year with the specified number of centuries added. This is equivalent to calling plusYears(long) with the amount multiplied by 100. 
MILLENNIA - Returns a Year with the specified number of millennia added. This is equivalent to calling plusYears(long) with the amount multiplied by 1,000. 
ERAS - Returns a Year 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. 
 All other ChronoUnit instances will throw an UnsupportedTemporalTypeException. 
 If the field is not a ChronoUnit, then the result of this method is obtained by invoking TemporalUnit.addTo(Temporal, long) passing this as the argument. In this case, the unit determines whether and how to perform the addition. 

This instance is immutable and unaffected by this method call.
Params: amountToAdd –  the amount of the unit to add to the result, may be negative
unit –  the unit of the amount to add, not null
Throws: DateTimeException – if the addition cannot be made
UnsupportedTemporalTypeException – if the unit is not supported
ArithmeticException – if numeric overflow occurs
Returns: a Year based on this year with the specified amount added, not null/**
     * Returns a copy of this year with the specified amount added.
     * <p>
     * This returns a {@code Year}, 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 YEARS} -
     *  Returns a {@code Year} with the specified number of years added.
     *  This is equivalent to {@link #plusYears(long)}.
     * <li>{@code DECADES} -
     *  Returns a {@code Year} 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 Year} 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 Year} 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 Year} 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 Year} based on this year 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 Year plus(long amountToAdd, TemporalUnit unit) {
        if (unit instanceof ChronoUnit) {
            switch ((ChronoUnit) unit) {
                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 Year with the specified number of years added. 
This instance is immutable and unaffected by this method call.
Params: yearsToAdd –  the years to add, may be negative
Throws: DateTimeException – if the result exceeds the supported range
Returns: a Year based on this year with the years added, not null/**
     * Returns a copy of this {@code Year} 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 Year} based on this year with the years added, not null
     * @throws DateTimeException if the result exceeds the supported range
     */
    public Year plusYears(long yearsToAdd) {
        if (yearsToAdd == 0) {
            return this;
        }
        return of(YEAR.checkValidIntValue(year + yearsToAdd));  // overflow safe
    }

    //-----------------------------------------------------------------------
    Returns a copy of this year with the specified amount subtracted.
 This returns a Year, based on this one, with the specified amount subtracted. The amount is typically Period but may be any other type implementing the TemporalAmount interface. 
 The calculation is delegated to the amount object by calling TemporalAmount.subtractFrom(Temporal). The amount implementation is free to implement the subtraction in any way it wishes, however it typically calls back to minus(long, TemporalUnit). Consult the documentation of the amount implementation to determine if it can be successfully subtracted. 

This instance is immutable and unaffected by this method call.
Params: amountToSubtract –  the amount to subtract, not null
Throws: DateTimeException – if the subtraction cannot be made
ArithmeticException – if numeric overflow occurs
Returns: a Year based on this year with the subtraction made, not null/**
     * Returns a copy of this year with the specified amount subtracted.
     * <p>
     * This returns a {@code Year}, 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 Year} based on this year with the subtraction made, not null
     * @throws DateTimeException if the subtraction cannot be made
     * @throws ArithmeticException if numeric overflow occurs
     */
    @Override
    public Year minus(TemporalAmount amountToSubtract) {
        return (Year) amountToSubtract.subtractFrom(this);
    }

    Returns a copy of this year with the specified amount subtracted.
 This returns a Year, 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. 
 This method is equivalent to plus(long, TemporalUnit) with the amount negated. See that method for a full description of how addition, and thus subtraction, works. 

This instance is immutable and unaffected by this method call.
Params: amountToSubtract –  the amount of the unit to subtract from the result, may be negative
unit –  the unit of the amount to subtract, not null
Throws: DateTimeException – if the subtraction cannot be made
UnsupportedTemporalTypeException – if the unit is not supported
ArithmeticException – if numeric overflow occurs
Returns: a Year based on this year with the specified amount subtracted, not null/**
     * Returns a copy of this year with the specified amount subtracted.
     * <p>
     * This returns a {@code Year}, 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 Year} based on this year 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 Year 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 Year with the specified number of years subtracted. 
This instance is immutable and unaffected by this method call.
Params: yearsToSubtract –  the years to subtract, may be negative
Throws: DateTimeException – if the result exceeds the supported range
Returns: a Year based on this year with the year subtracted, not null/**
     * Returns a copy of this {@code Year} 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 Year} based on this year with the year subtracted, not null
     * @throws DateTimeException if the result exceeds the supported range
     */
    public Year minusYears(long yearsToSubtract) {
        return (yearsToSubtract == Long.MIN_VALUE ? plusYears(Long.MAX_VALUE).plusYears(1) : plusYears(-yearsToSubtract));
    }

    //-----------------------------------------------------------------------
    Queries this year using the specified query.
 This queries this year using the specified query strategy object. The 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. 
 The result of this method is obtained by invoking the TemporalQuery.queryFrom(TemporalAccessor) method on the specified query passing this as the argument. 
Params: query –  the query to invoke, not null
Type parameters: <R> – the type of the result
Throws: DateTimeException – if unable to query (defined by the query)
ArithmeticException – if numeric overflow occurs (defined by the query)
Returns: the query result, null may be returned (defined by the query)/**
     * Queries this year using the specified query.
     * <p>
     * This queries this year 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) YEARS;
        }
        return Temporal.super.query(query);
    }

    Adjusts the specified temporal object to have this year.

This returns a temporal object of the same observable type as the input
with the year changed to be the same as this.
 The adjustment is equivalent to using Temporal.with(TemporalField, long) passing ChronoField.YEAR as the field. If the specified temporal object does not use the ISO calendar system then a DateTimeException is thrown. 
 In most cases, it is clearer to reverse the calling pattern by using Temporal.with(TemporalAdjuster): 
  // these two lines are equivalent, but the second approach is recommended
  temporal = thisYear.adjustInto(temporal);
  temporal = temporal.with(thisYear);


This instance is immutable and unaffected by this method call.
Params: temporal –  the target object to be adjusted, not null
Throws: DateTimeException – if unable to make the adjustment
ArithmeticException – if numeric overflow occurs
Returns: the adjusted object, not null/**
     * Adjusts the specified temporal object to have this year.
     * <p>
     * This returns a temporal object of the same observable type as the input
     * with the year changed to be the same as this.
     * <p>
     * The adjustment is equivalent to using {@link Temporal#with(TemporalField, long)}
     * passing {@link ChronoField#YEAR} 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 = thisYear.adjustInto(temporal);
     *   temporal = temporal.with(thisYear);
     * </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(YEAR, year);
    }

    Calculates the amount of time until another year in terms of the specified unit.
 This calculates the amount of time between two Year objects in terms of a single TemporalUnit. The start and end points are this and the specified year. The result will be negative if the end is before the start. The Temporal passed to this method is converted to a Year using from(TemporalAccessor). For example, the amount in decades between two year can be calculated using startYear.until(endYear, DECADES). 

The calculation returns a whole number, representing the number of
complete units between the two years.
For example, the amount in decades between 2012 and 2031
will only be one decade as it is one year short of two decades.
 There are two equivalent ways of using this method. The first is to invoke this method. The second is to use TemporalUnit.between(Temporal, Temporal): 
  // these two lines are equivalent
  amount = start.until(end, YEARS);
  amount = YEARS.between(start, end);

The choice should be made based on which makes the code more readable.
 The calculation is implemented in this method for ChronoUnit. The units YEARS, DECADES, CENTURIES, MILLENNIA and ERAS are supported. Other ChronoUnit values will throw an exception. 
 If the unit is not a ChronoUnit, then the result of this method is obtained by invoking TemporalUnit.between(Temporal, Temporal) passing this as the first argument and the converted input temporal as the second argument. 

This instance is immutable and unaffected by this method call.
Params: endExclusive –  the end date, exclusive, which is converted to a Year, not null
unit –  the unit to measure the amount in, not null
Throws: DateTimeException – if the amount cannot be calculated, or the end temporal cannot be converted to a Year
UnsupportedTemporalTypeException – if the unit is not supported
ArithmeticException – if numeric overflow occurs
Returns: the amount of time between this year and the end year/**
     * Calculates the amount of time until another year in terms of the specified unit.
     * <p>
     * This calculates the amount of time between two {@code Year}
     * objects in terms of a single {@code TemporalUnit}.
     * The start and end points are {@code this} and the specified year.
     * The result will be negative if the end is before the start.
     * The {@code Temporal} passed to this method is converted to a
     * {@code Year} using {@link #from(TemporalAccessor)}.
     * For example, the amount in decades between two year can be calculated
     * using {@code startYear.until(endYear, DECADES)}.
     * <p>
     * The calculation returns a whole number, representing the number of
     * complete units between the two years.
     * For example, the amount in decades between 2012 and 2031
     * will only be one decade as it is one year 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, YEARS);
     *   amount = YEARS.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 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 Year}, not null
     * @param unit  the unit to measure the amount in, not null
     * @return the amount of time between this year and the end year
     * @throws DateTimeException if the amount cannot be calculated, or the end
     *  temporal cannot be converted to a {@code Year}
     * @throws UnsupportedTemporalTypeException if the unit is not supported
     * @throws ArithmeticException if numeric overflow occurs
     */
    @Override
    public long until(Temporal endExclusive, TemporalUnit unit) {
        Year end = Year.from(endExclusive);
        if (unit instanceof ChronoUnit) {
            long yearsUntil = ((long) end.year) - year;  // no overflow
            switch ((ChronoUnit) unit) {
                case YEARS: return yearsUntil;
                case DECADES: return yearsUntil / 10;
                case CENTURIES: return yearsUntil / 100;
                case MILLENNIA: return yearsUntil / 1000;
                case ERAS: return end.getLong(ERA) - getLong(ERA);
            }
            throw new UnsupportedTemporalTypeException("Unsupported unit: " + unit);
        }
        return unit.between(this, end);
    }

    Formats this year using the specified formatter.

This year will be passed to the formatter to produce a string.
Params: formatter –  the formatter to use, not null
Throws: DateTimeException – if an error occurs during printing
Returns: the formatted year string, not null/**
     * Formats this year using the specified formatter.
     * <p>
     * This year will be passed to the formatter to produce a string.
     *
     * @param formatter  the formatter to use, not null
     * @return the formatted year 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 with a day-of-year to create a LocalDate.  This returns a LocalDate formed from this year and the specified day-of-year. 

The day-of-year value 366 is only valid in a leap year.
Params: dayOfYear –  the day-of-year to use, from 1 to 365-366
Throws: DateTimeException – if the day of year is zero or less, 366 or greater or equal
 to 366 and this is not a leap year
Returns: the local date formed from this year and the specified date of year, not null/**
     * Combines this year with a day-of-year to create a {@code LocalDate}.
     * <p>
     * This returns a {@code LocalDate} formed from this year and the specified day-of-year.
     * <p>
     * The day-of-year value 366 is only valid in a leap year.
     *
     * @param dayOfYear  the day-of-year to use, from 1 to 365-366
     * @return the local date formed from this year and the specified date of year, not null
     * @throws DateTimeException if the day of year is zero or less, 366 or greater or equal
     *  to 366 and this is not a leap year
     */
    public LocalDate atDay(int dayOfYear) {
        return LocalDate.ofYearDay(year, dayOfYear);
    }

    Combines this year with a month to create a YearMonth.  This returns a YearMonth formed from this year and the specified month. All possible combinations of year and month are valid. 

This method can be used as part of a chain to produce a date:
 LocalDate date = year.atMonth(month).atDay(day);

Params: month –  the month-of-year to use, not null
Returns: the year-month formed from this year and the specified month, not null/**
     * Combines this year with a month to create a {@code YearMonth}.
     * <p>
     * This returns a {@code YearMonth} formed from this year and the specified month.
     * All possible combinations of year and month are valid.
     * <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 month  the month-of-year to use, not null
     * @return the year-month formed from this year and the specified month, not null
     */
    public YearMonth atMonth(Month month) {
        return YearMonth.of(year, month);
    }

    Combines this year with a month to create a YearMonth.  This returns a YearMonth formed from this year and the specified month. All possible combinations of year and month are valid. 

This method can be used as part of a chain to produce a date:
 LocalDate date = year.atMonth(month).atDay(day);

Params: month –  the month-of-year to use, from 1 (January) to 12 (December)
Throws: DateTimeException – if the month is invalid
Returns: the year-month formed from this year and the specified month, not null/**
     * Combines this year with a month to create a {@code YearMonth}.
     * <p>
     * This returns a {@code YearMonth} formed from this year and the specified month.
     * All possible combinations of year and month are valid.
     * <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 month  the month-of-year to use, from 1 (January) to 12 (December)
     * @return the year-month formed from this year and the specified month, not null
     * @throws DateTimeException if the month is invalid
     */
    public YearMonth atMonth(int month) {
        return YearMonth.of(year, month);
    }

    Combines this year with a month-day to create a LocalDate.  This returns a LocalDate formed from this year and the specified month-day. 

A month-day of February 29th will be adjusted to February 28th in the resulting
date if the year is not a leap year.
Params: monthDay –  the month-day to use, not null
Returns: the local date formed from this year and the specified month-day, not null/**
     * Combines this year with a month-day to create a {@code LocalDate}.
     * <p>
     * This returns a {@code LocalDate} formed from this year and the specified month-day.
     * <p>
     * A month-day of February 29th will be adjusted to February 28th in the resulting
     * date if the year is not a leap year.
     *
     * @param monthDay  the month-day to use, not null
     * @return the local date formed from this year and the specified month-day, not null
     */
    public LocalDate atMonthDay(MonthDay monthDay) {
        return monthDay.atYear(year);
    }

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

    Checks if this year is after the specified year.
Params: other –  the other year to compare to, not null
Returns: true if this is after the specified year/**
     * Checks if this year is after the specified year.
     *
     * @param other  the other year to compare to, not null
     * @return true if this is after the specified year
     */
    public boolean isAfter(Year other) {
        return year > other.year;
    }

    Checks if this year is before the specified year.
Params: other –  the other year to compare to, not null
Returns: true if this point is before the specified year/**
     * Checks if this year is before the specified year.
     *
     * @param other  the other year to compare to, not null
     * @return true if this point is before the specified year
     */
    public boolean isBefore(Year other) {
        return year < other.year;
    }

    //-----------------------------------------------------------------------
    Checks if this year is equal to another year.

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

    A hash code for this year.
Returns: a suitable hash code/**
     * A hash code for this year.
     *
     * @return a suitable hash code
     */
    @Override
    public int hashCode() {
        return year;
    }

    //-----------------------------------------------------------------------
    Outputs this year as a String. 
Returns: a string representation of this year, not null/**
     * Outputs this year as a {@code String}.
     *
     * @return a string representation of this year, not null
     */
    @Override
    public String toString() {
        return Integer.toString(year);
    }

    //-----------------------------------------------------------------------
    Writes the object using a
dedicated serialized form.
@serialData 
 out.writeByte(11);  // identifies a Year
 out.writeInt(year);
Returns: the instance of Ser, not null/**
     * Writes the object using a
     * <a href="../../serialized-form.html#java.time.Ser">dedicated serialized form</a>.
     * @serialData
     * <pre>
     *  out.writeByte(11);  // identifies a Year
     *  out.writeInt(year);
     * </pre>
     *
     * @return the instance of {@code Ser}, not null
     */
    private Object writeReplace() {
        return new Ser(Ser.YEAR_TYPE, this);
    }

    Defend against malicious streams.
Params: s – the stream to read
Throws: InvalidObjectException – always/**
     * 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);
    }

    static Year readExternal(DataInput in) throws IOException {
        return Year.of(in.readInt());
    }

}
Implementation Requirements:	This class is immutable and thread-safe.
Since:	1.8
Params:	zone – the zone ID to use, not null
Returns:	the current year using the system clock, not null
Params:	clock – the clock to use, not null
Returns:	the current year, not null
Params:	isoYear – the ISO proleptic year to represent, from `MIN_VALUE` to `MAX_VALUE`
Throws:	DateTimeException – if the field is invalid
Returns:	the year, not null
Params:	temporal – the temporal object to convert, not null
Throws:	DateTimeException – if unable to convert to a `Year`
Returns:	the year, not null
Params:	text – the text to parse such as "2007", not null
Throws:	DateTimeParseException – if the text cannot be parsed
Returns:	the parsed year, not null
Params:	text – the text to parse, not null formatter – the formatter to use, not null
Throws:	DateTimeParseException – if the text cannot be parsed
Returns:	the parsed year, not null
Params:	year – the year to check
Returns:	true if the year is leap, false otherwise
Params:	field – the field to check, null returns false
Returns:	true if the field is supported on this year, false if not
Params:	unit – the unit to check, null returns false
Returns:	true if the unit can be added/subtracted, false if not
Params:	field – the field to query the range for, not null
Throws:	DateTimeException – if the range for the field cannot be obtained UnsupportedTemporalTypeException – if the field is not supported
Returns:	the range of valid values for the field, not null
Params:	field – the field to get, not null
Throws:	DateTimeException – if a value for the field cannot be obtained or the value is outside the range of valid values for the field UnsupportedTemporalTypeException – if the field is not supported or the range of values exceeds an `int` ArithmeticException – if numeric overflow occurs
Returns:	the value for the field
Params:	monthDay – the month-day to validate, null returns false
Returns:	true if the month and day are valid for this year
Params:	adjuster – the adjuster to use, not null
Throws:	DateTimeException – if the adjustment cannot be made ArithmeticException – if numeric overflow occurs
Returns:	a `Year` based on `this` with the adjustment made, not null
Params:	field – the field to set in the result, not null newValue – the new value of the field in the result
Throws:	DateTimeException – if the field cannot be set UnsupportedTemporalTypeException – if the field is not supported ArithmeticException – if numeric overflow occurs
Returns:	a `Year` based on `this` with the specified field set, not null
Params:	amountToAdd – the amount to add, not null
Throws:	DateTimeException – if the addition cannot be made ArithmeticException – if numeric overflow occurs
Returns:	a `Year` based on this year with the addition made, not null
Params:	amountToAdd – the amount of the unit to add to the result, may be negative unit – the unit of the amount to add, not null
Throws:	DateTimeException – if the addition cannot be made UnsupportedTemporalTypeException – if the unit is not supported ArithmeticException – if numeric overflow occurs
Returns:	a `Year` based on this year with the specified amount added, not null
Params:	yearsToAdd – the years to add, may be negative
Throws:	DateTimeException – if the result exceeds the supported range
Returns:	a `Year` based on this year with the years added, not null
Params:	amountToSubtract – the amount to subtract, not null
Throws:	DateTimeException – if the subtraction cannot be made ArithmeticException – if numeric overflow occurs
Returns:	a `Year` based on this year with the subtraction made, not null
Params:	amountToSubtract – the amount of the unit to subtract from the result, may be negative unit – the unit of the amount to subtract, not null
Throws:	DateTimeException – if the subtraction cannot be made UnsupportedTemporalTypeException – if the unit is not supported ArithmeticException – if numeric overflow occurs
Returns:	a `Year` based on this year with the specified amount subtracted, not null
/

java/ 11/ java.base/java/time/Year.java
