# Class IsoChronology

java.lang.Object
java.time.chrono.AbstractChronology
java.time.chrono.IsoChronology

All Implemented Interfaces:
  `Serializable`, `Comparable<Chronology>`, `Chronology`

public final class IsoChronology extends AbstractChronology implements Serializable
The ISO calendar system.

This chronology defines the rules of the ISO calendar system. This calendar system is based on the ISO-8601 standard, which is the de facto world calendar.

The fields are defined as follows:

- era - There are two eras, 'Current Era' (CE) and 'Before Current Era' (BCE).
- year-of-era - The year-of-era is the same as the proleptic-year for the current CE era. For the BCE era before the ISO epoch the year increases from 1 upwards as time goes backwards.
- proleptic-year - The proleptic year is the same as the year-of-era for the current era. For the previous era, years have zero, then negative values.
- month-of-year - There are 12 months in an ISO year, numbered from 1 to 12.
- day-of-month - There are between 28 and 31 days in each of the ISO month, numbered from 1 to 31. Months 4, 6, 9 and 11 have 30 days, Months 1, 3, 5, 7, 8, 10 and 12 have 31 days. Month 2 has 28 days, or 29 in a leap year.
- day-of-year - There are 365 days in a standard ISO year and 366 in a leap year. The days are numbered from 1 to 365 or 1 to 366.
- leap-year - Leap years occur every 4 years, except where the year is divisble by 100 and not divisble by 400.

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

- ## Field Summary

  Fields
  Modifier and Type
  Field
  Description
  `static final IsoChronology`
  `INSTANCE`
  Singleton instance of the ISO chronology.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `LocalDate`
  `date(int prolepticYear, int month, int dayOfMonth)`
  Obtains an ISO local date from the proleptic-year, month-of-year and day-of-month fields.
  `LocalDate`
  `date(Era era, int yearOfEra, int month, int dayOfMonth)`
  Obtains an ISO local date from the era, year-of-era, month-of-year and day-of-month fields.
  `LocalDate`
  `date(TemporalAccessor temporal)`
  Obtains an ISO local date from another date-time object.
  `LocalDate`
  `dateEpochDay(long epochDay)`
  Obtains an ISO local date from the epoch-day.
  `LocalDate`
  `dateNow()`
  Obtains the current ISO local date from the system clock in the default time-zone.
  `LocalDate`
  `dateNow(Clock clock)`
  Obtains the current ISO local date from the specified clock.
  `LocalDate`
  `dateNow(ZoneId zone)`
  Obtains the current ISO local date from the system clock in the specified time-zone.
  `LocalDate`
  `dateYearDay(int prolepticYear, int dayOfYear)`
  Obtains an ISO local date from the proleptic-year and day-of-year fields.
  `LocalDate`
  `dateYearDay(Era era, int yearOfEra, int dayOfYear)`
  Obtains an ISO local date from the era, year-of-era and day-of-year fields.
  `long`
  `epochSecond(int prolepticYear, int month, int dayOfMonth, int hour, int minute, int second, ZoneOffset zoneOffset)`
  Gets the number of seconds from the epoch of 1970-01-01T00:00:00Z.
  `IsoEra`
  `eraOf(int eraValue)`
  Creates the chronology era object from the numeric value.
  `List<Era>`
  `eras()`
  Gets the list of eras for the chronology.
  `String`
  `getCalendarType()`
  Gets the calendar type of the underlying calendar system - 'iso8601'.
  `String`
  `getId()`
  Gets the ID of the chronology - 'ISO'.
  `boolean`
  `isIsoBased()`
  `IsoChronology` is an ISO based chronology, which supports fields in `IsoFields`, such as `DAY_OF_QUARTER` and `QUARTER_OF_YEAR`.
  `boolean`
  `isLeapYear(long prolepticYear)`
  Checks if the year is a leap year, according to the ISO proleptic calendar system rules.
  `LocalDateTime`
  `localDateTime(TemporalAccessor temporal)`
  Obtains an ISO local date-time from another date-time object.
  `Period`
  `period(int years, int months, int days)`
  Obtains a period for this chronology based on years, months and days.
  `int`
  `prolepticYear(Era era, int yearOfEra)`
  Calculates the proleptic-year given the era and year-of-era.
  `ValueRange`
  `range(ChronoField field)`
  Gets the range of valid values for the specified field.
  `LocalDate`
  `resolveDate(Map<TemporalField, Long> fieldValues, ResolverStyle resolverStyle)`
  Resolves parsed `ChronoField` values into a date during parsing.
  `ZonedDateTime`
  `zonedDateTime(Instant instant, ZoneId zone)`
  Obtains an ISO zoned date-time in this chronology from an `Instant`.
  `ZonedDateTime`
  `zonedDateTime(TemporalAccessor temporal)`
  Obtains an ISO zoned date-time from another date-time object.

  ### Methods declared in class java.time.chrono.AbstractChronology

  `compareTo, equals, hashCode, toString`

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

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

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

  `epochSecond, getDisplayName`

- ## Field Details

  - ### INSTANCE

    public static final IsoChronology INSTANCE
    Singleton instance of the ISO chronology.

- ## Method Details

  - ### getId

    public String getId()
    Gets the ID of the chronology - 'ISO'.

    The ID uniquely identifies the `Chronology`. It can be used to lookup the `Chronology` using `Chronology.of(String)`.

    Specified by:
      `getId` in interface `Chronology`
    Returns:
      the chronology ID - 'ISO'
    See Also:
      - `getCalendarType()`

  - ### getCalendarType

    public String getCalendarType()
    Gets the calendar type of the underlying calendar system - 'iso8601'.

    The calendar type is an identifier defined by the Unicode Locale Data Markup Language (LDML) specification. It can be used to lookup the `Chronology` using `Chronology.of(String)`. It can also be used as part of a locale, accessible via `Locale.getUnicodeLocaleType(String)` with the key 'ca'.

    Specified by:
      `getCalendarType` in interface `Chronology`
    Returns:
      the calendar system type - 'iso8601'
    See Also:
      - `getId()`

  - ### date

    public LocalDate date(Era era, int yearOfEra, int month, int dayOfMonth)
    Obtains an ISO local date from the era, year-of-era, month-of-year and day-of-month fields.
    Specified by:
      `date` in interface `Chronology`
    Parameters:
      `era` - the ISO era, not null
      `yearOfEra` - the ISO year-of-era
      `month` - the ISO month-of-year
      `dayOfMonth` - the ISO day-of-month
    Returns:
      the ISO local date, not null
    Throws:
      `DateTimeException` - if unable to create the date
      `ClassCastException` - if the type of `era` is not `IsoEra`

  - ### date

    public LocalDate date(int prolepticYear, int month, int dayOfMonth)
    Obtains an ISO local date from the proleptic-year, month-of-year and day-of-month fields.

    This is equivalent to `LocalDate.of(int, int, int)`.

    Specified by:
      `date` in interface `Chronology`
    Parameters:
      `prolepticYear` - the ISO proleptic-year
      `month` - the ISO month-of-year
      `dayOfMonth` - the ISO day-of-month
    Returns:
      the ISO local date, not null
    Throws:
      `DateTimeException` - if unable to create the date

  - ### dateYearDay

    public LocalDate dateYearDay(Era era, int yearOfEra, int dayOfYear)
    Obtains an ISO local date from the era, year-of-era and day-of-year fields.
    Specified by:
      `dateYearDay` in interface `Chronology`
    Parameters:
      `era` - the ISO era, not null
      `yearOfEra` - the ISO year-of-era
      `dayOfYear` - the ISO day-of-year
    Returns:
      the ISO local date, not null
    Throws:
      `DateTimeException` - if unable to create the date

  - ### dateYearDay

    public LocalDate dateYearDay(int prolepticYear, int dayOfYear)
    Obtains an ISO local date from the proleptic-year and day-of-year fields.

    This is equivalent to `LocalDate.ofYearDay(int, int)`.

    Specified by:
      `dateYearDay` in interface `Chronology`
    Parameters:
      `prolepticYear` - the ISO proleptic-year
      `dayOfYear` - the ISO day-of-year
    Returns:
      the ISO local date, not null
    Throws:
      `DateTimeException` - if unable to create the date

  - ### dateEpochDay

    public LocalDate dateEpochDay(long epochDay)
    Obtains an ISO local date from the epoch-day.

    This is equivalent to `LocalDate.ofEpochDay(long)`.

    Specified by:
      `dateEpochDay` in interface `Chronology`
    Parameters:
      `epochDay` - the epoch day
    Returns:
      the ISO local date, not null
    Throws:
      `DateTimeException` - if unable to create the date

  - ### date

    public LocalDate date(TemporalAccessor temporal)
    Obtains an ISO local date from another date-time object.

    This is equivalent to `LocalDate.from(TemporalAccessor)`.

    Specified by:
      `date` in interface `Chronology`
    Parameters:
      `temporal` - the date-time object to convert, not null
    Returns:
      the ISO local date, not null
    Throws:
      `DateTimeException` - if unable to create the date
    See Also:
      - `ChronoLocalDate.from(TemporalAccessor)`

  - ### epochSecond

    public long epochSecond(int prolepticYear, int month, int dayOfMonth, int hour, int minute, int second, ZoneOffset zoneOffset)
    Gets the number of seconds from the epoch of 1970-01-01T00:00:00Z.

    The number of seconds is calculated using the year, month, day-of-month, hour, minute, second, and zoneOffset.

    Specified by:
      `epochSecond` in interface `Chronology`
    Parameters:
      `prolepticYear` - the year, from MIN_YEAR to MAX_YEAR
      `month` - the month-of-year, from 1 to 12
      `dayOfMonth` - the day-of-month, from 1 to 31
      `hour` - the hour-of-day, from 0 to 23
      `minute` - the minute-of-hour, from 0 to 59
      `second` - the second-of-minute, from 0 to 59
      `zoneOffset` - the zone offset, not null
    Returns:
      the number of seconds relative to 1970-01-01T00:00:00Z, may be negative
    Throws:
      `DateTimeException` - if the value of any argument is out of range, or if the day-of-month is invalid for the month-of-year
    Since:
      9

  - ### localDateTime

    public LocalDateTime localDateTime(TemporalAccessor temporal)
    Obtains an ISO local date-time from another date-time object.

    This is equivalent to `LocalDateTime.from(TemporalAccessor)`.

    Specified by:
      `localDateTime` in interface `Chronology`
    Parameters:
      `temporal` - the date-time object to convert, not null
    Returns:
      the ISO local date-time, not null
    Throws:
      `DateTimeException` - if unable to create the date-time
    See Also:
      - `ChronoLocalDateTime.from(TemporalAccessor)`

  - ### zonedDateTime

    public ZonedDateTime zonedDateTime(TemporalAccessor temporal)
    Obtains an ISO zoned date-time from another date-time object.

    This is equivalent to `ZonedDateTime.from(TemporalAccessor)`.

    Specified by:
      `zonedDateTime` in interface `Chronology`
    Parameters:
      `temporal` - the date-time object to convert, not null
    Returns:
      the ISO zoned date-time, not null
    Throws:
      `DateTimeException` - if unable to create the date-time
    See Also:
      - `ChronoZonedDateTime.from(TemporalAccessor)`

  - ### zonedDateTime

    public ZonedDateTime zonedDateTime(Instant instant, ZoneId zone)
    Obtains an ISO zoned date-time in this chronology from an `Instant`.

    This is equivalent to `ZonedDateTime.ofInstant(Instant, ZoneId)`.

    Specified by:
      `zonedDateTime` in interface `Chronology`
    Parameters:
      `instant` - the instant to create the date-time from, not null
      `zone` - the time-zone, not null
    Returns:
      the zoned date-time, not null
    Throws:
      `DateTimeException` - if the result exceeds the supported range

  - ### dateNow

    public LocalDate dateNow()
    Obtains the current ISO local date 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.

    Specified by:
      `dateNow` in interface `Chronology`
    Returns:
      the current ISO local date using the system clock and default time-zone, not null
    Throws:
      `DateTimeException` - if unable to create the date

  - ### dateNow

    public LocalDate dateNow(ZoneId zone)
    Obtains the current ISO local date 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.

    Specified by:
      `dateNow` in interface `Chronology`
    Parameters:
      `zone` - the zone ID to use, not null
    Returns:
      the current ISO local date using the system clock, not null
    Throws:
      `DateTimeException` - if unable to create the date

  - ### dateNow

    public LocalDate dateNow(Clock clock)
    Obtains the current ISO local date 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`.

    Specified by:
      `dateNow` in interface `Chronology`
    Parameters:
      `clock` - the clock to use, not null
    Returns:
      the current ISO local date, not null
    Throws:
      `DateTimeException` - if unable to create the date

  - ### isLeapYear

    public boolean isLeapYear(long prolepticYear)
    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.

    Specified by:
      `isLeapYear` in interface `Chronology`
    Parameters:
      `prolepticYear` - the ISO proleptic year to check
    Returns:
      true if the year is leap, false otherwise

  - ### prolepticYear

    public int prolepticYear(Era era, int yearOfEra)
    Description copied from interface: `Chronology`
    Calculates the proleptic-year given the era and year-of-era.

    This combines the era and year-of-era into the single proleptic-year field.

    If the chronology makes active use of eras, such as `JapaneseChronology` then the year-of-era will be validated against the era. For other chronologies, validation is optional.

    Specified by:
      `prolepticYear` in interface `Chronology`
    Parameters:
      `era` - the era of the correct type for the chronology, not null
      `yearOfEra` - the chronology year-of-era
    Returns:
      the proleptic-year

  - ### eraOf

    public IsoEra eraOf(int eraValue)
    Description copied from interface: `Chronology`
    Creates the chronology era object from the numeric value.

    The era is, conceptually, the largest division of the time-line. Most calendar systems have a single epoch dividing the time-line into two eras. However, some have multiple eras, such as one for the reign of each leader. The exact meaning is determined by the chronology according to the following constraints.

    The era in use at 1970-01-01 must have the value 1. Later eras must have sequentially higher values. Earlier eras must have sequentially lower values. Each chronology must refer to an enum or similar singleton to provide the era values.

    This method returns the singleton era of the correct type for the specified era value.

    Specified by:
      `eraOf` in interface `Chronology`
    Parameters:
      `eraValue` - the era value
    Returns:
      the calendar system era, not null

  - ### eras

    public List<Era> eras()
    Description copied from interface: `Chronology`
    Gets the list of eras for the chronology.

    Most calendar systems have an era, within which the year has meaning. If the calendar system does not support the concept of eras, an empty list must be returned.

    Specified by:
      `eras` in interface `Chronology`
    Returns:
      the list of eras for the chronology, may be immutable, not null

  - ### resolveDate

    public LocalDate resolveDate(Map<TemporalField, Long> fieldValues, ResolverStyle resolverStyle)
    Resolves parsed `ChronoField` values into a date during parsing.

    Most `TemporalField` implementations are resolved using the resolve method on the field. By contrast, the `ChronoField` class defines fields that only have meaning relative to the chronology. As such, `ChronoField` date fields are resolved here in the context of a specific chronology.

    `ChronoField` instances on the ISO calendar system are resolved as follows.

    - `EPOCH_DAY` - If present, this is converted to a `LocalDate` and all other date fields are then cross-checked against the date.
    - `PROLEPTIC_MONTH` - If present, then it is split into the `YEAR` and `MONTH_OF_YEAR`. If the mode is strict or smart then the field is validated.
    - `YEAR_OF_ERA` and `ERA` - If both are present, then they are combined to form a `YEAR`. In lenient mode, the `YEAR_OF_ERA` range is not validated, in smart and strict mode it is. The `ERA` is validated for range in all three modes. If only the `YEAR_OF_ERA` is present, and the mode is smart or lenient, then the current era (CE/AD) is assumed. In strict mode, no era is assumed and the `YEAR_OF_ERA` is left untouched. If only the `ERA` is present, then it is left untouched.
    - `YEAR`, `MONTH_OF_YEAR` and `DAY_OF_MONTH` - If all three are present, then they are combined to form a `LocalDate`. In all three modes, the `YEAR` is validated. If the mode is smart or strict, then the month and day are validated, with the day validated from 1 to 31. If the mode is lenient, then the date is combined in a manner equivalent to creating a date on the first of January in the requested year, then adding the difference in months, then the difference in days. If the mode is smart, and the day-of-month is greater than the maximum for the year-month, then the day-of-month is adjusted to the last day-of-month. If the mode is strict, then the three fields must form a valid date.
    - `YEAR` and `DAY_OF_YEAR` - If both are present, then they are combined to form a `LocalDate`. In all three modes, the `YEAR` is validated. If the mode is lenient, then the date is combined in a manner equivalent to creating a date on the first of January in the requested year, then adding the difference in days. If the mode is smart or strict, then the two fields must form a valid date.
    - `YEAR`, `MONTH_OF_YEAR`, `ALIGNED_WEEK_OF_MONTH` and `ALIGNED_DAY_OF_WEEK_IN_MONTH` - If all four are present, then they are combined to form a `LocalDate`. In all three modes, the `YEAR` is validated. If the mode is lenient, then the date is combined in a manner equivalent to creating a date on the first of January in the requested year, then adding the difference in months, then the difference in weeks, then in days. If the mode is smart or strict, then the all four fields are validated to their outer ranges. The date is then combined in a manner equivalent to creating a date on the first day of the requested year and month, then adding the amount in weeks and days to reach their values. If the mode is strict, the date is additionally validated to check that the day and week adjustment did not change the month.
    - `YEAR`, `MONTH_OF_YEAR`, `ALIGNED_WEEK_OF_MONTH` and `DAY_OF_WEEK` - If all four are present, then they are combined to form a `LocalDate`. The approach is the same as described above for years, months and weeks in `ALIGNED_DAY_OF_WEEK_IN_MONTH`. The day-of-week is adjusted as the next or same matching day-of-week once the years, months and weeks have been handled.
    - `YEAR`, `ALIGNED_WEEK_OF_YEAR` and `ALIGNED_DAY_OF_WEEK_IN_YEAR` - If all three are present, then they are combined to form a `LocalDate`. In all three modes, the `YEAR` is validated. If the mode is lenient, then the date is combined in a manner equivalent to creating a date on the first of January in the requested year, then adding the difference in weeks, then in days. If the mode is smart or strict, then the all three fields are validated to their outer ranges. The date is then combined in a manner equivalent to creating a date on the first day of the requested year, then adding the amount in weeks and days to reach their values. If the mode is strict, the date is additionally validated to check that the day and week adjustment did not change the year.
    - `YEAR`, `ALIGNED_WEEK_OF_YEAR` and `DAY_OF_WEEK` - If all three are present, then they are combined to form a `LocalDate`. The approach is the same as described above for years and weeks in `ALIGNED_DAY_OF_WEEK_IN_YEAR`. The day-of-week is adjusted as the next or same matching day-of-week once the years and weeks have been handled.
    Specified by:
      `resolveDate` in interface `Chronology`
    Overrides:
      `resolveDate` in class `AbstractChronology`
    Parameters:
      `fieldValues` - the map of fields to values, which can be updated, not null
      `resolverStyle` - the requested type of resolve, not null
    Returns:
      the resolved date, null if insufficient information to create a date
    Throws:
      `DateTimeException` - if the date cannot be resolved, typically because of a conflict in the input data

  - ### range

    public ValueRange range(ChronoField field)
    Description copied from interface: `Chronology`
    Gets the range of valid values for the specified field.

    All fields can be expressed as a `long` integer. This method returns an object that describes the valid range for that value.

    Note that the result only describes the minimum and maximum valid values and it is important not to read too much into them. For example, there could be values within the range that are invalid for the field.

    This method will return a result whether or not the chronology supports the field.

    Specified by:
      `range` in interface `Chronology`
    Parameters:
      `field` - the field to get the range for, not null
    Returns:
      the range of valid values for the field, not null

  - ### period

    public Period period(int years, int months, int days)
    Obtains a period for this chronology based on years, months and days.

    This returns a period tied to the ISO chronology using the specified years, months and days. See `Period` for further details.

    Specified by:
      `period` in interface `Chronology`
    Parameters:
      `years` - the number of years, may be negative
      `months` - the number of years, may be negative
      `days` - the number of years, may be negative
    Returns:
      the ISO period, not null

  - ### isIsoBased

    public boolean isIsoBased()
    `IsoChronology` is an ISO based chronology, which supports fields in `IsoFields`, such as `DAY_OF_QUARTER` and `QUARTER_OF_YEAR`.
    Specified by:
      `isIsoBased` in interface `Chronology`
    Returns:
      `true`
    Since:
      19
    See Also:
      - `IsoFields`