Module java.base
Package java.time.chrono

# Class JapaneseDate

java.lang.Object
java.time.chrono.JapaneseDate

All Implemented Interfaces:
  `Serializable`, `Comparable<ChronoLocalDate>`, `ChronoLocalDate`, `Temporal`, `TemporalAccessor`, `TemporalAdjuster`

public final class JapaneseDate extends Object implements ChronoLocalDate, Serializable
A date in the Japanese Imperial calendar system.

This date operates using the Japanese Imperial calendar. This calendar system is primarily used in Japan.

The Japanese Imperial calendar system is the same as the ISO calendar system apart from the era-based year numbering. The proleptic-year is defined to be equal to the ISO proleptic-year.

Japan introduced the Gregorian calendar starting with Meiji 6. Only Meiji and later eras are supported; dates before Meiji 6, January 1 are not supported.

For example, the Japanese year "Heisei 24" corresponds to ISO year "2012".
Calling `japaneseDate.get(YEAR_OF_ERA)` will return 24.
Calling `japaneseDate.get(YEAR)` will return 2012.
Calling `japaneseDate.get(ERA)` will return 2, corresponding to `JapaneseChronology.ERA_HEISEI`.

This is a value-based class; programmers should treat instances that are equal as interchangeable and should not use instances for synchronization, or unpredictable behavior may occur. For example, in a future release, synchronization may fail. The `equals` method should be used for comparisons.

Implementation Requirements:
  This class is immutable and thread-safe.
Since:
  1.8
See Also:
  - Serialized Form

- ## Method Summary

  Modifier and Type
  Method
  Description
  `final ChronoLocalDateTime<JapaneseDate>`
  `atTime(LocalTime localTime)`
  Combines this date with a time to create a `ChronoLocalDateTime`.
  `boolean`
  `equals(Object obj)`
  Compares this date to another date, including the chronology.
  `static JapaneseDate`
  `from(TemporalAccessor temporal)`
  Obtains a `JapaneseDate` from a temporal object.
  `JapaneseChronology`
  `getChronology()`
  Gets the chronology of this date, which is the Japanese calendar system.
  `JapaneseEra`
  `getEra()`
  Gets the era applicable at this date.
  `long`
  `getLong(TemporalField field)`
  Gets the value of the specified field as a `long`.
  `int`
  `hashCode()`
  A hash code for this date.
  `boolean`
  `isSupported(TemporalField field)`
  Checks if the specified field is supported.
  `int`
  `lengthOfMonth()`
  Returns the length of the month represented by this date.
  `JapaneseDate`
  `minus(long amountToSubtract, TemporalUnit unit)`
  Returns an object of the same type as this object with the specified period subtracted.
  `JapaneseDate`
  `minus(TemporalAmount amount)`
  Returns an object of the same type as this object with an amount subtracted.
  `static JapaneseDate`
  `now()`
  Obtains the current `JapaneseDate` from the system clock in the default time-zone.
  `static JapaneseDate`
  `now(Clock clock)`
  Obtains the current `JapaneseDate` from the specified clock.
  `static JapaneseDate`
  `now(ZoneId zone)`
  Obtains the current `JapaneseDate` from the system clock in the specified time-zone.
  `static JapaneseDate`
  `of(int prolepticYear, int month, int dayOfMonth)`
  Obtains a `JapaneseDate` representing a date in the Japanese calendar system from the proleptic-year, month-of-year and day-of-month fields.
  `static JapaneseDate`
  `of(JapaneseEra era, int yearOfEra, int month, int dayOfMonth)`
  Obtains a `JapaneseDate` representing a date in the Japanese calendar system from the era, year-of-era, month-of-year and day-of-month fields.
  `JapaneseDate`
  `plus(long amountToAdd, TemporalUnit unit)`
  Returns an object of the same type as this object with the specified period added.
  `JapaneseDate`
  `plus(TemporalAmount amount)`
  Returns an object of the same type as this object with an amount added.
  `String`
  `toString()`
  Returns a string representation of the object.
  `ChronoPeriod`
  `until(ChronoLocalDate endDate)`
  Calculates the period between this date and another date as a `ChronoPeriod`.
  `long`
  `until(Temporal endExclusive, TemporalUnit unit)`
  Calculates the amount of time until another date in terms of the specified unit.
  `JapaneseDate`
  `with(TemporalAdjuster adjuster)`
  Returns an adjusted object of the same type as this object with the adjustment made.
  `JapaneseDate`
  `with(TemporalField field, long newValue)`
  Returns an object of the same type as this object with the specified field altered.

  ### Methods declared in class java.lang.Object

  `clone, finalize, getClass, notify, notifyAll, wait, wait, wait`

  ### Methods declared in interface java.time.chrono.ChronoLocalDate

  `adjustInto, compareTo, format, isAfter, isBefore, isEqual, isLeapYear, isSupported, lengthOfYear, query, toEpochDay, toString, until`

  ### Methods declared in interface java.time.temporal.TemporalAccessor

  `get, range`

- ## Method Details

  - ### now

    public static JapaneseDate now()
    Obtains the current `JapaneseDate` from the system clock in the default time-zone.

    This will query the `system clock` in the default time-zone to obtain the current date.

    Using this method will prevent the ability to use an alternate clock for testing because the clock is hard-coded.

    Returns:
      the current date using the system clock and default time-zone, not null

  - ### now

    public static JapaneseDate now(ZoneId zone)
    Obtains the current `JapaneseDate` from the system clock in the specified time-zone.

    This will query the `system clock` to obtain the current date. 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.

    Parameters:
      `zone` - the zone ID to use, not null
    Returns:
      the current date using the system clock, not null

  - ### now

    public static JapaneseDate now(Clock clock)
    Obtains the current `JapaneseDate` from the specified clock.

    This will query the specified clock to obtain the current date - today. Using this method allows the use of an alternate clock for testing. The alternate clock may be introduced using dependency injection.

    Parameters:
      `clock` - the clock to use, not null
    Returns:
      the current date, not null
    Throws:
      `DateTimeException` - if the current date cannot be obtained

  - ### of

    public static JapaneseDate of(JapaneseEra era, int yearOfEra, int month, int dayOfMonth)
    Obtains a `JapaneseDate` representing a date in the Japanese calendar system from the era, year-of-era, month-of-year and day-of-month fields.

    This returns a `JapaneseDate` with the specified fields. The day must be valid for the year and month, otherwise an exception will be thrown.

    The Japanese month and day-of-month are the same as those in the ISO calendar system. They are not reset when the era changes. For example:

          6th Jan Showa 64 = ISO 1989-01-06
          7th Jan Showa 64 = ISO 1989-01-07
          8th Jan Heisei 1 = ISO 1989-01-08
          9th Jan Heisei 1 = ISO 1989-01-09

    Parameters:
      `era` - the Japanese era, not null
      `yearOfEra` - the Japanese year-of-era
      `month` - the Japanese month-of-year, from 1 to 12
      `dayOfMonth` - the Japanese day-of-month, from 1 to 31
    Returns:
      the date in Japanese calendar system, not null
    Throws:
      `DateTimeException` - if the value of any field is out of range, or if the day-of-month is invalid for the month-year, or if the date is not a Japanese era

  - ### of

    public static JapaneseDate of(int prolepticYear, int month, int dayOfMonth)
    Obtains a `JapaneseDate` representing a date in the Japanese calendar system from the proleptic-year, month-of-year and day-of-month fields.

    This returns a `JapaneseDate` with the specified fields. The day must be valid for the year and month, otherwise an exception will be thrown.

    The Japanese proleptic year, month and day-of-month are the same as those in the ISO calendar system. They are not reset when the era changes.

    Parameters:
      `prolepticYear` - the Japanese proleptic-year
      `month` - the Japanese month-of-year, from 1 to 12
      `dayOfMonth` - the Japanese day-of-month, from 1 to 31
    Returns:
      the date in Japanese calendar system, not null
    Throws:
      `DateTimeException` - if the value of any field is out of range, or if the day-of-month is invalid for the month-year

  - ### from

    public static JapaneseDate from(TemporalAccessor temporal)
    Obtains a `JapaneseDate` from a temporal object.

    This obtains a date in the Japanese calendar system based on the specified temporal. A `TemporalAccessor` represents an arbitrary set of date and time information, which this factory converts to an instance of `JapaneseDate`.

    The conversion typically uses the `EPOCH_DAY` field, which is standardized across calendar systems.

    This method matches the signature of the functional interface `TemporalQuery` allowing it to be used as a query via method reference, `JapaneseDate::from`.

    Parameters:
      `temporal` - the temporal object to convert, not null
    Returns:
      the date in Japanese calendar system, not null
    Throws:
      `DateTimeException` - if unable to convert to a `JapaneseDate`

  - ### getChronology

    public JapaneseChronology getChronology()
    Gets the chronology of this date, which is the Japanese calendar system.

    The `Chronology` represents the calendar system in use. The era and other fields in `ChronoField` are defined by the chronology.

    Specified by:
      `getChronology` in interface `ChronoLocalDate`
    Returns:
      the Japanese chronology, not null

  - ### getEra

    public JapaneseEra getEra()
    Gets the era applicable at this date.

    The Japanese calendar system has multiple eras defined by `JapaneseEra`.

    Specified by:
      `getEra` in interface `ChronoLocalDate`
    Returns:
      the era applicable at this date, not null

  - ### lengthOfMonth

    public int lengthOfMonth()
    Returns the length of the month represented by this date.

    This returns the length of the month in days. Month lengths match those of the ISO calendar system.

    Specified by:
      `lengthOfMonth` in interface `ChronoLocalDate`
    Returns:
      the length of the month in days

  - ### isSupported

    public boolean isSupported(TemporalField field)
    Checks if the specified field is supported.

    This checks if this date can be queried for the specified field. If false, then calling the `range` and `get` methods will throw an exception.

    If the field is a `ChronoField` then the query is implemented here. The supported fields are:

    - `DAY_OF_WEEK`
    - `DAY_OF_MONTH`
    - `DAY_OF_YEAR`
    - `EPOCH_DAY`
    - `MONTH_OF_YEAR`
    - `PROLEPTIC_MONTH`
    - `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.

    Specified by:
      `isSupported` in interface `ChronoLocalDate`
    Specified by:
      `isSupported` in interface `TemporalAccessor`
    Parameters:
      `field` - the field to check, null returns false
    Returns:
      true if the field is supported on this date, false if not

  - ### getLong

    public long getLong(TemporalField field)
    Description copied from interface: `TemporalAccessor`
    Gets the value of the specified field as a `long`.

    This queries the date-time for the value of the specified field. The returned value may be outside the valid range of values for the field. If the date-time cannot return the value, because the field is unsupported or for some other reason, an exception will be thrown.

    Specified by:
      `getLong` in interface `TemporalAccessor`
    Parameters:
      `field` - the field to get, not null
    Returns:
      the value for the field

  - ### with

    public JapaneseDate with(TemporalField field, long newValue)
    Description copied from interface: `ChronoLocalDate`
    Returns an object of the same type as this object with the specified field altered.

    This returns a new object based on this one with the value for the specified field changed. For example, on a `LocalDate`, this could be used to set the year, month or day-of-month. The returned object will have the same observable type as this object.

    In some cases, changing a field is not fully defined. For example, if the target object is a date representing the 31st January, then changing the month to February would be unclear. In cases like this, the field is responsible for resolving the result. Typically it will choose the previous valid date, which would be the last valid day of February in this example.

    Specified by:
      `with` in interface `ChronoLocalDate`
    Specified by:
      `with` in interface `Temporal`
    Parameters:
      `field` - the field to set in the result, not null
      `newValue` - the new value of the field in the result
    Returns:
      an object of the same type with the specified field set, not null

  - ### with

    public JapaneseDate with(TemporalAdjuster adjuster)
    Returns an adjusted object of the same type as this object with the adjustment made.

    This adjusts this date-time according to the rules of the specified adjuster. A simple adjuster might simply set the one of the fields, such as the year field. A more complex adjuster might set the date to the last day of the month. A selection of common adjustments is provided in `TemporalAdjusters`. These include finding the "last day of the month" and "next Wednesday". The adjuster is responsible for handling special cases, such as the varying lengths of month and leap years.

    Some example code indicating how and why this method is used:

          date = date.with(Month.JULY);        // most key classes implement TemporalAdjuster
          date = date.with(lastDayOfMonth());  // static import from Adjusters
          date = date.with(next(WEDNESDAY));   // static import from Adjusters and DayOfWeek

    Specified by:
      `with` in interface `ChronoLocalDate`
    Specified by:
      `with` in interface `Temporal`
    Parameters:
      `adjuster` - the adjuster to use, not null
    Returns:
      an object of the same type with the specified adjustment made, not null
    Throws:
      `DateTimeException` - if unable to make the adjustment
      `ArithmeticException` - if numeric overflow occurs

  - ### plus

    public JapaneseDate plus(TemporalAmount amount)
    Returns an object of the same type as this object with an amount added.

    This adjusts this temporal, adding according to the rules of the specified amount. The amount is typically a `Period` but may be any other type implementing the `TemporalAmount` interface, such as `Duration`.

    Some example code indicating how and why this method is used:

          date = date.plus(period);                // add a Period instance
          date = date.plus(duration);              // add a Duration instance
          date = date.plus(workingDays(6));        // example user-written workingDays method

    Note that calling `plus` followed by `minus` is not guaranteed to return the same date-time.

    Specified by:
      `plus` in interface `ChronoLocalDate`
    Specified by:
      `plus` in interface `Temporal`
    Parameters:
      `amount` - the amount to add, not null
    Returns:
      an object of the same type with the specified adjustment made, not null
    Throws:
      `DateTimeException` - if the addition cannot be made
      `ArithmeticException` - if numeric overflow occurs

  - ### minus

    public JapaneseDate minus(TemporalAmount amount)
    Returns an object of the same type as this object with an amount subtracted.

    This adjusts this temporal, subtracting according to the rules of the specified amount. The amount is typically a `Period` but may be any other type implementing the `TemporalAmount` interface, such as `Duration`.

    Some example code indicating how and why this method is used:

          date = date.minus(period);               // subtract a Period instance
          date = date.minus(duration);             // subtract a Duration instance
          date = date.minus(workingDays(6));       // example user-written workingDays method

    Note that calling `plus` followed by `minus` is not guaranteed to return the same date-time.

    Specified by:
      `minus` in interface `ChronoLocalDate`
    Specified by:
      `minus` in interface `Temporal`
    Parameters:
      `amount` - the amount to subtract, not null
    Returns:
      an object of the same type with the specified adjustment made, not null
    Throws:
      `DateTimeException` - if the subtraction cannot be made
      `ArithmeticException` - if numeric overflow occurs

  - ### plus

    public JapaneseDate plus(long amountToAdd, TemporalUnit unit)
    Description copied from interface: `ChronoLocalDate`
    Returns an object of the same type as this object with the specified period added.

    This method returns a new object based on this one with the specified period added. For example, on a `LocalDate`, this could be used to add a number of years, months or days. The returned object will have the same observable type as this object.

    In some cases, changing a field is not fully defined. For example, if the target object is a date representing the 31st January, then adding one month would be unclear. In cases like this, the field is responsible for resolving the result. Typically it will choose the previous valid date, which would be the last valid day of February in this example.

    Specified by:
      `plus` in interface `ChronoLocalDate`
    Specified by:
      `plus` in interface `Temporal`
    Parameters:
      `amountToAdd` - the amount of the specified unit to add, may be negative
      `unit` - the unit of the amount to add, not null
    Returns:
      an object of the same type with the specified period added, not null

  - ### minus

    public JapaneseDate minus(long amountToSubtract, TemporalUnit unit)
    Description copied from interface: `ChronoLocalDate`
    Returns an object of the same type as this object with the specified period subtracted.

    This method returns a new object based on this one with the specified period subtracted. For example, on a `LocalDate`, this could be used to subtract a number of years, months or days. The returned object will have the same observable type as this object.

    In some cases, changing a field is not fully defined. For example, if the target object is a date representing the 31st March, then subtracting one month would be unclear. In cases like this, the field is responsible for resolving the result. Typically it will choose the previous valid date, which would be the last valid day of February in this example.

    Specified by:
      `minus` in interface `ChronoLocalDate`
    Specified by:
      `minus` in interface `Temporal`
    Parameters:
      `amountToSubtract` - the amount of the specified unit to subtract, may be negative
      `unit` - the unit of the amount to subtract, not null
    Returns:
      an object of the same type with the specified period subtracted, not null

  - ### atTime

    public final ChronoLocalDateTime<JapaneseDate> atTime(LocalTime localTime)
    Description copied from interface: `ChronoLocalDate`
    Combines this date with a time to create a `ChronoLocalDateTime`.

    This returns a `ChronoLocalDateTime` formed from this date at the specified time. All possible combinations of date and time are valid.

    Specified by:
      `atTime` in interface `ChronoLocalDate`
    Parameters:
      `localTime` - the local time to use, not null
    Returns:
      the local date-time formed from this date and the specified time, not null

  - ### until

    public ChronoPeriod until(ChronoLocalDate endDate)
    Description copied from interface: `ChronoLocalDate`
    Calculates the period between this date and another date as a `ChronoPeriod`.

    This calculates the period between two dates. All supplied chronologies calculate the period using years, months and days, however the `ChronoPeriod` API allows the period to be represented using other units.

    The start and end points are `this` and the specified date. The result will be negative if the end is before the start. The negative sign will be the same in each of year, month and day.

    The calculation is performed using the chronology of this date. If necessary, the input date will be converted to match.

    This instance is immutable and unaffected by this method call.

    Specified by:
      `until` in interface `ChronoLocalDate`
    Parameters:
      `endDate` - the end date, exclusive, which may be in any chronology, not null
    Returns:
      the period between this date and the end date, not null

  - ### equals

    public boolean equals(Object obj)
    Compares this date to another date, including the chronology.

    Compares this `JapaneseDate` with another ensuring that the date is the same.

    Only objects of type `JapaneseDate` are compared, other types return false. To compare the dates of two `TemporalAccessor` instances, including dates in two different chronologies, use `ChronoField.EPOCH_DAY` as a comparator.

    Specified by:
      `equals` in interface `ChronoLocalDate`
    Parameters:
      `obj` - the object to check, null returns false
    Returns:
      true if this is equal to the other date
    See Also:
      - `Object.hashCode()`
      - `HashMap`

  - ### hashCode

    public int hashCode()
    A hash code for this date.
    Specified by:
      `hashCode` in interface `ChronoLocalDate`
    Returns:
      a suitable hash code based only on the Chronology and the date
    See Also:
      - `Object.equals(java.lang.Object)`
      - `System.identityHashCode(java.lang.Object)`

  - ### until

    public long until(Temporal endExclusive, TemporalUnit unit)
    Description copied from interface: `ChronoLocalDate`
    Calculates the amount of time until another date in terms of the specified unit.

    This calculates the amount of time between two `ChronoLocalDate` objects in terms of a single `TemporalUnit`. The start and end points are `this` and the specified date. The result will be negative if the end is before the start. The `Temporal` passed to this method is converted to a `ChronoLocalDate` using `Chronology.date(TemporalAccessor)`. The calculation returns a whole number, representing the number of complete units between the two dates. For example, the amount in days between two dates can be calculated using `startDate.until(endDate, DAYS)`.

    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, MONTHS);
           amount = MONTHS.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 `DAYS`, `WEEKS`, `MONTHS`, `YEARS`, `DECADES`, `CENTURIES`, `MILLENNIA` and `ERAS` should be supported by all implementations. 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.

    Specified by:
      `until` in interface `ChronoLocalDate`
    Specified by:
      `until` in interface `Temporal`
    Parameters:
      `endExclusive` - the end date, exclusive, which is converted to a `ChronoLocalDate` in the same chronology, not null
      `unit` - the unit to measure the amount in, not null
    Returns:
      the amount of time between this date and the end date

  - ### toString

    public String toString()
    Description copied from class: `Object`
    Returns a string representation of the object.
    Specified by:
      `toString` in interface `ChronoLocalDate`
    Overrides:
      `toString` in class `Object`
    Returns:
      a string representation of the object.