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# IsoChronology

`public final class IsoChronology`
`` `extends AbstractChronology` `implements Serializable`

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

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.

## Summary

### Fields
`public static final IsoChronology` | `INSTANCE` Singleton instance of the ISO chronology.

### Public methods
`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(ZoneId zone)` Obtains the current ISO local date from the system clock in the specified time-zone.
`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` | `dateYearDay(Era era, int yearOfEra, int dayOfYear)` Obtains an ISO local date from the era, year-of-era and day-of-year fields.
`LocalDate` | `dateYearDay(int prolepticYear, int dayOfYear)` Obtains an ISO local date from the proleptic-year and day-of-year fields.
`IsoEra` | `eraOf(int eraValue)`
`List<Era>` | `eras()`
`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.
`int` | `prolepticYear(Era era, int yearOfEra)`
`ValueRange` | `range(ChronoField field)`
`LocalDate` | `resolveDate(Map<TemporalField, Long> fieldValues, ResolverStyle resolverStyle)` Resolves parsed `ChronoField` values into a date during parsing.
`ZonedDateTime` | `zonedDateTime(TemporalAccessor temporal)` Obtains an ISO zoned date-time from another date-time object.
`ZonedDateTime` | `zonedDateTime(Instant instant, ZoneId zone)` Obtains an ISO zoned date-time in this chronology from an `Instant`.

### Inherited methods
From class `java.time.chrono.AbstractChronology`
`int` | `compareTo(Chronology other)` Compares this chronology to another chronology.
`boolean` | `equals(Object obj)` Checks if this chronology is equal to another chronology.
`int` | `hashCode()` A hash code for this chronology.
`ChronoLocalDate` | `resolveDate(Map<TemporalField, Long> fieldValues, ResolverStyle resolverStyle)` Resolves parsed `ChronoField` values into a date during parsing.
`String` | `toString()` Outputs this chronology as a `String`, using the chronology ID.
From class `java.lang.Object`
`Object` | `clone()` Creates and returns a copy of this object.
`boolean` | `equals(Object obj)` Indicates whether some other object is "equal to" this one.
`void` | `finalize()` Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.
`final Class<?>` | `getClass()` Returns the runtime class of this `Object`.
`int` | `hashCode()` Returns a hash code value for the object.
`final void` | `notify()` Wakes up a single thread that is waiting on this object's monitor.
`final void` | `notifyAll()` Wakes up all threads that are waiting on this object's monitor.
`String` | `toString()` Returns a string representation of the object.
`final void` | `wait(long timeout, int nanos)` Causes the current thread to wait until another thread invokes the `notify()` method or the `notifyAll()` method for this object, or some other thread interrupts the current thread, or a certain amount of real time has elapsed.
`final void` | `wait(long timeout)` Causes the current thread to wait until either another thread invokes the `notify()` method or the `notifyAll()` method for this object, or a specified amount of time has elapsed.
`final void` | `wait()` Causes the current thread to wait until another thread invokes the `notify()` method or the `notifyAll()` method for this object.
From interface `java.time.chrono.Chronology`
`abstract int` | `compareTo(Chronology other)` Compares this chronology to another chronology.
`default ChronoLocalDate` | `date(Era era, int yearOfEra, int month, int dayOfMonth)` Obtains a local date in this chronology from the era, year-of-era, month-of-year and day-of-month fields.
`abstract ChronoLocalDate` | `date(int prolepticYear, int month, int dayOfMonth)` Obtains a local date in this chronology from the proleptic-year, month-of-year and day-of-month fields.
`abstract ChronoLocalDate` | `date(TemporalAccessor temporal)` Obtains a local date in this chronology from another temporal object.
`abstract ChronoLocalDate` | `dateEpochDay(long epochDay)` Obtains a local date in this chronology from the epoch-day.
`default ChronoLocalDate` | `dateNow(Clock clock)` Obtains the current local date in this chronology from the specified clock.
`default ChronoLocalDate` | `dateNow(ZoneId zone)` Obtains the current local date in this chronology from the system clock in the specified time-zone.
`default ChronoLocalDate` | `dateNow()` Obtains the current local date in this chronology from the system clock in the default time-zone.
`default ChronoLocalDate` | `dateYearDay(Era era, int yearOfEra, int dayOfYear)` Obtains a local date in this chronology from the era, year-of-era and day-of-year fields.
`abstract ChronoLocalDate` | `dateYearDay(int prolepticYear, int dayOfYear)` Obtains a local date in this chronology from the proleptic-year and day-of-year fields.
`abstract boolean` | `equals(Object obj)` Checks if this chronology is equal to another chronology.
`abstract Era` | `eraOf(int eraValue)` Creates the chronology era object from the numeric value.
`abstract List<Era>` | `eras()` Gets the list of eras for the chronology.
`static Chronology` | `from(TemporalAccessor temporal)` Obtains an instance of `Chronology` from a temporal object.
`static Set<Chronology>` | `getAvailableChronologies()` Returns the available chronologies.
`abstract String` | `getCalendarType()` Gets the calendar type of the calendar system.
`default String` | `getDisplayName(TextStyle style, Locale locale)` Gets the textual representation of this chronology.
`abstract String` | `getId()` Gets the ID of the chronology.
`abstract int` | `hashCode()` A hash code for this chronology.
`abstract boolean` | `isLeapYear(long prolepticYear)` Checks if the specified year is a leap year.
`default ChronoLocalDateTime<? extends ChronoLocalDate>` | `localDateTime(TemporalAccessor temporal)` Obtains a local date-time in this chronology from another temporal object.
`static Chronology` | `of(String id)` Obtains an instance of `Chronology` from a chronology ID or calendar system type.
`static Chronology` | `ofLocale(Locale locale)` Obtains an instance of `Chronology` from a locale.
`default ChronoPeriod` | `period(int years, int months, int days)` Obtains a period for this chronology based on years, months and days.
`abstract int` | `prolepticYear(Era era, int yearOfEra)` Calculates the proleptic-year given the era and year-of-era.
`abstract ValueRange` | `range(ChronoField field)` Gets the range of valid values for the specified field.
`abstract ChronoLocalDate` | `resolveDate(Map<TemporalField, Long> fieldValues, ResolverStyle resolverStyle)` Resolves parsed `ChronoField` values into a date during parsing.
`abstract String` | `toString()` Outputs this chronology as a `String`.
`default ChronoZonedDateTime<? extends ChronoLocalDate>` | `zonedDateTime(Instant instant, ZoneId zone)` Obtains a `ChronoZonedDateTime` in this chronology from an `Instant`.
`default ChronoZonedDateTime<? extends ChronoLocalDate>` | `zonedDateTime(TemporalAccessor temporal)` Obtains a `ChronoZonedDateTime` in this chronology from another temporal object.
From interface `java.lang.Comparable`
`abstract int` | `compareTo(Chronology o)` Compares this object with the specified object for order.

## Fields

### INSTANCE

    public static final IsoChronology INSTANCE

Singleton instance of the ISO chronology.

## Public methods

### 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)`.

Parameters
`prolepticYear` | `int`: the ISO proleptic-year
`month` | `int`: the ISO month-of-year
`dayOfMonth` | `int`: the ISO day-of-month

Returns
`LocalDate` | the ISO local date, not null

Throws
`DateTimeException` | if unable to create the date

### 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.

Parameters
`era` | `Era`: the ISO era, not null
`yearOfEra` | `int`: the ISO year-of-era
`month` | `int`: the ISO month-of-year
`dayOfMonth` | `int`: the ISO day-of-month

Returns
`LocalDate` | 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 (TemporalAccessor temporal)

Obtains an ISO local date from another date-time object.

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

Parameters
`temporal` | `TemporalAccessor`: the date-time object to convert, not null

Returns
`LocalDate` | 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)`.

Parameters
`epochDay` | `long`: the epoch day

Returns
`LocalDate` | the ISO local date, 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.

Parameters
`zone` | `ZoneId`

Returns
`LocalDate` | the current ISO local date using the system clock, not null

Throws
`DateTimeException` | if unable to create the date

### 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.

Returns
`LocalDate` | 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 (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`.

Parameters
`clock` | `Clock`: the clock to use, not null

Returns
`LocalDate` | the current 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.

Parameters
`era` | `Era`: the ISO era, not null
`yearOfEra` | `int`: the ISO year-of-era
`dayOfYear` | `int`: the ISO day-of-year

Returns
`LocalDate` | 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)`.

Parameters
`prolepticYear` | `int`: the ISO proleptic-year
`dayOfYear` | `int`: the ISO day-of-year

Returns
`LocalDate` | the ISO local date, not null

Throws
`DateTimeException` | if unable to create the date

### eraOf

    public IsoEra eraOf (int eraValue)

Parameters
`eraValue` | `int`

Returns
`IsoEra` |

### eras

    public List<Era> eras ()

Returns
`List<Era>` |

### 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'.

Returns
`String` | the calendar system type - 'iso8601'

See also:

- `getId()`

### 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)`.

Returns
`String` | the chronology ID - 'ISO'

See also:

- `getCalendarType()`

### 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.

Parameters
`prolepticYear` | `long`: the ISO proleptic year to check

Returns
`boolean` | true if the year is leap, false otherwise

### localDateTime

    public LocalDateTime localDateTime (TemporalAccessor temporal)

Obtains an ISO local date-time from another date-time object.

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

Parameters
`temporal` | `TemporalAccessor`: the date-time object to convert, not null

Returns
`LocalDateTime` | the ISO local date-time, not null

Throws
`DateTimeException` | if unable to create the date-time

### 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.

Parameters
`years` | `int`: the number of years, may be negative
`months` | `int`: the number of years, may be negative
`days` | `int`: the number of years, may be negative

Returns
`Period` | the period in terms of this chronology, not nullthe ISO period, not null

### prolepticYear

    public int prolepticYear (Era era,
                    int yearOfEra)

Parameters
`era` | `Era`
`yearOfEra` | `int`

Returns
`int` |

### range

    public ValueRange range (ChronoField field)

Parameters
`field` | `ChronoField`

Returns
`ValueRange` |

### 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.

Parameters
`fieldValues` | `Map`: the map of fields to values, which can be updated, not null
`resolverStyle` | `ResolverStyle`: the requested type of resolve, not null

Returns
`LocalDate` | 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

### zonedDateTime

    public ZonedDateTime zonedDateTime (TemporalAccessor temporal)

Obtains an ISO zoned date-time from another date-time object.

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

Parameters
`temporal` | `TemporalAccessor`: the date-time object to convert, not null

Returns
`ZonedDateTime` | the ISO zoned date-time, not null

Throws
`DateTimeException` | if unable to create the date-time

### 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)`.

Parameters
`instant` | `Instant`: the instant to create the date-time from, not null
`zone` | `ZoneId`: the time-zone, not null

Returns
`ZonedDateTime` | the zoned date-time, not null

Throws
`DateTimeException` | if the result exceeds the supported range

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