Module java.base
Package java.time.chrono

## 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 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.
    `String` | `getCalendarType()` | Gets the calendar type of the underlying calendar system - 'iso8601'.
    `String` | `getId()` | Gets the ID of the chronology - 'ISO'.
    `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.
    `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, eraOf, eras, getDisplayName, prolepticYear, range`

- - ### Field Detail

    - #### INSTANCE

          public static final IsoChronology INSTANCE

      Singleton instance of the ISO chronology.

  - ### Method Detail

    - #### 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

    - #### 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

    - #### 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