Chronology (ThreeTen backport for java.time package 1.0.0 API)

java.lang.Object
- java.time.chrono.Chronology

All Implemented Interfaces:

java.lang.Comparable<Chronology>

Direct Known Subclasses:

AbstractChronology, HijrahChronology, IsoChronology, JapaneseChronology, MinguoChronology, ThaiBuddhistChronology
```
public abstract class Chronology
extends java.lang.Object
implements java.lang.Comparable<Chronology>
```
A calendar system, used to organize and identify dates.
The main date and time API is built on the ISO calendar system. This class operates behind the scenes to represent the general concept of a calendar system. For example, the Japanese, Minguo, Thai Buddhist and others.
Most other calendar systems also operate on the shared concepts of year, month and day, linked to the cycles of the Earth around the Sun, and the Moon around the Earth. These shared concepts are defined by ChronoField and are availalbe for use by any Chronology implementation:
```
   LocalDate isoDate = ...
   ChronoLocalDate<ThaiBuddhistChrono> minguoDate = ...
   int isoYear = isoDate.get(ChronoField.YEAR);
   int thaiYear = thaiDate.get(ChronoField.YEAR);
 
```
As shown, although the date objects are in different calendar systems, represented by different Chronology instances, both can be queried using the same constant on ChronoField. For a full discussion of the implications of this, see ChronoLocalDate. In general, the advice is to use the known ISO-based LocalDate, rather than ChronoLocalDate.
While a Chronology object typically uses ChronoField and is based on an era, year-of-era, month-of-year, day-of-month model of a date, this is not required. A Chronology instance may represent a totally different kind of calendar system, such as the Mayan.
In practical terms, the Chronology instance also acts as a factory. The of(String) method allows an instance to be looked up by identifier, while the ofLocale(Locale) method allows lookup by locale.
The Chronology instance provides a set of methods to create ChronoLocalDate instances. The date classes are used to manipulate specific dates.
Adding New Calendars
The set of available chronologies can be extended by applications. Adding a new calendar system requires the writing of an implementation of Chronology, ChronoLocalDate and Era. The majority of the logic specific to the calendar system will be in ChronoLocalDate. The Chronology subclass acts as a factory.
To permit the discovery of additional chronologies, the ServiceLoader is used. A file must be added to the META-INF/services directory with the name 'java.bp.chrono.Chrono' listing the implementation classes. See the ServiceLoader for more details on service loading. For lookup by id or calendarType, the system provided calendars are found first followed by application provided calendars.
Each chronology must define a chronology ID that is unique within the system. If the chronology represents a calendar system defined by the Unicode Locale Data Markup Language (LDML) specification then that calendar type should also be specified.
Specification for implementors
This class must be implemented with care to ensure other classes operate correctly. All implementations that can be instantiated must be final, immutable and thread-safe. Subclasses should be Serializable wherever possible.
In JDK 8, this is an interface with default methods. Since there are no default methods in JDK 7, an abstract class is used.

Field Summary

Fields
Modifier and Type Field and Description

static TemporalQuery<Chronology> FROM
Simulate JDK 8 method reference Chronology::from.

Fields
Modifier and Type	Field and Description
`static TemporalQuery<Chronology>`	`FROM` Simulate JDK 8 method reference Chronology::from.

Constructor Summary

Constructors
Modifier Constructor and Description

protected Chronology()
Creates an instance.

Constructors
Modifier	Constructor and Description
`protected`	`Chronology()` Creates an instance.

Method Summary

Methods
Modifier and Type	Method and Description
`int`	`compareTo(Chronology other)` Compares this chronology to another chronology.
`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.
`ChronoLocalDate`	`dateNow()` Obtains the current local date in this chronology from the system clock in the default time-zone.
`ChronoLocalDate`	`dateNow(Clock clock)` Obtains the current local date in this chronology from the specified clock.
`ChronoLocalDate`	`dateNow(ZoneId zone)` Obtains the current local date in this chronology from the system clock in the specified time-zone.
`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.
`boolean`	`equals(java.lang.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 java.util.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 java.util.Set<Chronology>`	`getAvailableChronologies()` Returns the available chronologies.
`abstract java.lang.String`	`getCalendarType()` Gets the calendar type of the underlying calendar system.
`java.lang.String`	`getDisplayName(TextStyle style, java.util.Locale locale)` Gets the textual representation of this chronology.
`abstract java.lang.String`	`getId()` Gets the ID of the chronology.
`int`	`hashCode()` A hash code for this chronology.
`abstract boolean`	`isLeapYear(long prolepticYear)` Checks if the specified year is a leap year.
`ChronoLocalDateTime<?>`	`localDateTime(TemporalAccessor temporal)` Obtains a local date-time in this chronology from another temporal object.
`static Chronology`	`of(java.lang.String id)` Obtains an instance of `Chronology` from a chronology ID or calendar system type.
`static Chronology`	`ofLocale(java.util.Locale locale)` Obtains an instance of `Chronology` from a locale.
`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.
`ChronoLocalDate`	`resolveDate(java.util.Map<TemporalField,java.lang.Long> fieldValues, ResolverStyle resolverStyle)` Resolves parsed `ChronoField` values into a date during parsing.
`java.lang.String`	`toString()` Outputs this chronology as a `String`, using the ID.
`ChronoZonedDateTime<?>`	`zonedDateTime(Instant instant, ZoneId zone)` Obtains a zoned date-time in this chronology from an `Instant`.
`ChronoZonedDateTime<?>`	`zonedDateTime(TemporalAccessor temporal)` Obtains a zoned date-time in this chronology from another temporal object.

Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait

- Field Detail
  - FROM
```
public static final TemporalQuery<Chronology> FROM
```
    Simulate JDK 8 method reference Chronology::from.
- Constructor Detail
  - Chronology
```
protected Chronology()
```
    Creates an instance.
- Method Detail
  - from
```
public static Chronology from(TemporalAccessor temporal)
```
    Obtains an instance of Chronology from a temporal object.
    A TemporalAccessor represents some form of date and time information. This factory converts the arbitrary temporal object to an instance of Chronology. If the specified temporal object does not have a chronology, IsoChronology is returned.
    The conversion will obtain the chronology using TemporalQueries.chronology().
    This method matches the signature of the functional interface TemporalQuery allowing it to be used in queries via method reference, Chrono::from.
    
    Parameters:
    temporal - the temporal to convert, not null
    
    Returns:
    the chronology, not null
    
    Throws:
    
    DateTimeException - if unable to convert to an Chronology
  - ofLocale
```
public static Chronology ofLocale(java.util.Locale locale)
```
    Obtains an instance of Chronology from a locale.
    This returns a Chronology based on the specified locale, typically returning IsoChronology. Other calendar systems are only returned if they are explicitly selected within the locale.
    The Locale class provide access to a range of information useful for localizing an application. This includes the language and region, such as "en-GB" for English as used in Great Britain.
    The Locale class also supports an extension mechanism that can be used to identify a calendar system. The mechanism is a form of key-value pairs, where the calendar system has the key "ca". For example, the locale "en-JP-u-ca-japanese" represents the English language as used in Japan with the Japanese calendar system.
    This method finds the desired calendar system by in a manner equivalent to passing "ca" to Locale.getUnicodeLocaleType(String). If the "ca" key is not present, then IsoChronology is returned.
    Note that the behavior of this method differs from the older Calendar.getInstance(Locale) method. If that method receives a locale of "th_TH" it will return BuddhistCalendar. By contrast, this method will return IsoChronology. Passing the locale "th-TH-u-ca-buddhist" into either method will result in the Thai Buddhist calendar system and is therefore the recommended approach going forward for Thai calendar system localization.
    A similar, but simpler, situation occurs for the Japanese calendar system. The locale "jp_JP_JP" has previously been used to access the calendar. However, unlike the Thai locale, "ja_JP_JP" is automatically converted by Locale to the modern and recommended form of "ja-JP-u-ca-japanese". Thus, there is no difference in behavior between this method and Calendar#getInstance(Locale).
    
    Parameters:
    locale - the locale to use to obtain the calendar system, not null
    
    Returns:
    the calendar system associated with the locale, not null
    
    Throws:
    
    DateTimeException - if the locale-specified calendar cannot be found
  - of
```
public static Chronology of(java.lang.String id)
```
    Obtains an instance of Chronology from a chronology ID or calendar system type.
    This returns a chronology based on either the ID or the type. The chronology ID uniquely identifies the chronology. The calendar system type is defined by the LDML specification.
    The chronology may be a system chronology or a chronology provided by the application via ServiceLoader configuration.
    Since some calendars can be customized, the ID or type typically refers to the default customization. For example, the Gregorian calendar can have multiple cutover dates from the Julian, but the lookup only provides the default cutover date.
    
    Parameters:
    id - the chronology ID or calendar system type, not null
    
    Returns:
    the chronology with the identifier requested, not null
    
    Throws:
    
    DateTimeException - if the chronology cannot be found
  - getAvailableChronologies
```
public static java.util.Set<Chronology> getAvailableChronologies()
```
    Returns the available chronologies.
    Each returned Chronology is available for use in the system.
    
    Returns:
    the independent, modifiable set of the available chronology IDs, not null
  - getId
```
public abstract java.lang.String getId()
```
    Gets the ID of the chronology.
    The ID uniquely identifies the Chronology. It can be used to lookup the Chronology using of(String).
    
    Returns:
    the chronology ID, not null
    See Also:
    getCalendarType()
  - getCalendarType
```
public abstract java.lang.String getCalendarType()
```
    Gets the calendar type of the underlying calendar system.
    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 of(String). It can also be used as part of a locale, accessible via Locale.getUnicodeLocaleType(String) with the key 'ca'.
    
    Returns:
    the calendar system type, null if the calendar is not defined by LDML
    See Also:
    getId()
  - date
```
public 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.
    
    Parameters:
    era - the era of the correct type for the chronology, not null
    yearOfEra - the chronology year-of-era
    month - the chronology month-of-year
    dayOfMonth - the chronology day-of-month
    
    Returns:
    the local date in this chronology, not null
    
    Throws:
    
    DateTimeException - if unable to create the date
    
    java.lang.ClassCastException - if the era is not of the correct type for the chronology
  - date
```
public 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.
    
    Parameters:
    prolepticYear - the chronology proleptic-year
    month - the chronology month-of-year
    dayOfMonth - the chronology day-of-month
    
    Returns:
    the local date in this chronology, not null
    
    Throws:
    
    DateTimeException - if unable to create the date
  - dateYearDay
```
public 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.
    
    Parameters:
    era - the era of the correct type for the chronology, not null
    yearOfEra - the chronology year-of-era
    dayOfYear - the chronology day-of-year
    
    Returns:
    the local date in this chronology, not null
    
    Throws:
    
    DateTimeException - if unable to create the date
    
    java.lang.ClassCastException - if the era is not of the correct type for the chronology
  - dateYearDay
```
public abstract ChronoLocalDate dateYearDay(int prolepticYear,
                          int dayOfYear)
```
    Obtains a local date in this chronology from the proleptic-year and day-of-year fields.
    
    Parameters:
    prolepticYear - the chronology proleptic-year
    dayOfYear - the chronology day-of-year
    
    Returns:
    the local date in this chronology, not null
    
    Throws:
    
    DateTimeException - if unable to create the date
  - dateEpochDay
```
public abstract ChronoLocalDate dateEpochDay(long epochDay)
```
    Obtains a local date in this chronology from the epoch-day.
    The definition of EPOCH_DAY is the same for all calendar systems, thus it can be used for conversion.
    
    Parameters:
    epochDay - the epoch day
    
    Returns:
    the local date in this chronology, not null
    
    Throws:
    
    DateTimeException - if unable to create the date
  - date
```
public abstract ChronoLocalDate date(TemporalAccessor temporal)
```
    Obtains a local date in this chronology from another temporal object.
    This creates a date in this chronology based on the specified TemporalAccessor.
    The standard mechanism for conversion between date types is the local epoch-day field.
    
    Parameters:
    temporal - the temporal object to convert, not null
    
    Returns:
    the local date in this chronology, not null
    
    Throws:
    
    DateTimeException - if unable to create the date
  - dateNow
```
public ChronoLocalDate dateNow()
```
    Obtains the current local date in this chronology 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.
    This implementation uses dateNow(Clock).
    
    Returns:
    the current local date using the system clock and default time-zone, not null
    
    Throws:
    
    DateTimeException - if unable to create the date
  - dateNow
```
public ChronoLocalDate dateNow(ZoneId zone)
```
    Obtains the current local date in this chronology 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 local date using the system clock, not null
    
    Throws:
    
    DateTimeException - if unable to create the date
  - dateNow
```
public ChronoLocalDate dateNow(Clock clock)
```
    Obtains the current local date in this chronology 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 local date, not null
    
    Throws:
    
    DateTimeException - if unable to create the date
  - localDateTime
```
public ChronoLocalDateTime<?> localDateTime(TemporalAccessor temporal)
```
    Obtains a local date-time in this chronology from another temporal object.
    This creates a date-time in this chronology based on the specified TemporalAccessor.
    The date of the date-time should be equivalent to that obtained by calling date(TemporalAccessor). The standard mechanism for conversion between time types is the nano-of-day field.
    
    Parameters:
    temporal - the temporal object to convert, not null
    
    Returns:
    the local date-time in this chronology, not null
    
    Throws:
    
    DateTimeException - if unable to create the date-time
  - zonedDateTime
```
public ChronoZonedDateTime<?> zonedDateTime(TemporalAccessor temporal)
```
    Obtains a zoned date-time in this chronology from another temporal object.
    This creates a date-time in this chronology based on the specified TemporalAccessor.
    This should obtain a ZoneId using ZoneId.from(TemporalAccessor). The date-time should be obtained by obtaining an Instant. If that fails, the local date-time should be used.
    
    Parameters:
    temporal - the temporal object to convert, not null
    
    Returns:
    the zoned date-time in this chronology, not null
    
    Throws:
    
    DateTimeException - if unable to create the date-time
  - zonedDateTime
```
public ChronoZonedDateTime<?> zonedDateTime(Instant instant,
                                   ZoneId zone)
```
    Obtains a zoned date-time in this chronology from an Instant.
    This creates a zoned date-time with the same instant as that specified.
    
    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
  - period
```
public ChronoPeriod 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 this chronology using the specified years, months and days. All supplied chronologies use periods based on years, months and days, however the ChronoPeriod API allows the period to be represented using other units.
    The default implementation returns an implementation class suitable for most calendar systems. It is based solely on the three units. Normalization, addition and subtraction derive the number of months in a year from the range(ChronoField). If the number of months within a year is fixed, then the calculation approach for addition, subtraction and normalization is slightly different.
    If implementing an unusual calendar system that is not based on years, months and days, or where you want direct control, then the ChronoPeriod interface must be directly implemented.
    The returned period is immutable and thread-safe.
    
    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 period in terms of this chronology, not null
  - isLeapYear
```
public abstract boolean isLeapYear(long prolepticYear)
```
    Checks if the specified year is a leap year.
    A leap-year is a year of a longer length than normal. The exact meaning is determined by the chronology according to the following constraints.
    - a leap-year must imply a year-length longer than a non leap-year.
    - a chronology that does not support the concept of a year must return false.
    Parameters:
    prolepticYear - the proleptic-year to check, not validated for range
    
    Returns:
    true if the year is a leap year
  - prolepticYear
```
public abstract int prolepticYear(Era era,
                int yearOfEra)
```
    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.
    
    Parameters:
    era - the era of the correct type for the chronology, not null
    yearOfEra - the chronology year-of-era
    
    Returns:
    the proleptic-year
    
    Throws:
    
    DateTimeException - if unable to convert
    
    java.lang.ClassCastException - if the era is not of the correct type for the chronology
  - eraOf
```
public abstract Era eraOf(int eraValue)
```
    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.
    
    Parameters:
    eraValue - the era value
    
    Returns:
    the calendar system era, not null
    
    Throws:
    
    DateTimeException - if unable to create the era
  - eras
```
public abstract java.util.List<Era> eras()
```
    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.
    
    Returns:
    the list of eras for the chronology, may be immutable, not null
  - range
```
public abstract ValueRange range(ChronoField field)
```
    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.
    
    Parameters:
    field - the field to get the range for, not null
    
    Returns:
    the range of valid values for the field, not null
    
    Throws:
    
    DateTimeException - if the range for the field cannot be obtained
  - getDisplayName
```
public java.lang.String getDisplayName(TextStyle style,
                              java.util.Locale locale)
```
    Gets the textual representation of this chronology.
    This returns the textual name used to identify the chronology. The parameters control the style of the returned text and the locale.
    
    Parameters:
    style - the style of the text required, not null
    locale - the locale to use, not null
    
    Returns:
    the text value of the chronology, not null
  - resolveDate
```
public ChronoLocalDate resolveDate(java.util.Map<TemporalField,java.lang.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.
    The default implementation, which explains typical resolve behaviour, is provided in 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
  - compareTo
```
public int compareTo(Chronology other)
```
    Compares this chronology to another chronology.
    The comparison order first by the chronology ID string, then by any additional information specific to the subclass. It is "consistent with equals", as defined by Comparable.
    The default implementation compares the chronology ID. Subclasses must compare any additional state that they store.
    
    Specified by:
    
    compareTo in interface java.lang.Comparable<Chronology>
    
    Parameters:
    other - the other chronology to compare to, not null
    
    Returns:
    the comparator value, negative if less, positive if greater
  - equals
```
public boolean equals(java.lang.Object obj)
```
    Checks if this chronology is equal to another chronology.
    The comparison is based on the entire state of the object.
    The default implementation checks the type and calls compareTo(Chronology).
    
    Overrides:
    
    equals in class java.lang.Object
    
    Parameters:
    obj - the object to check, null returns false
    
    Returns:
    true if this is equal to the other chronology
  - hashCode
```
public int hashCode()
```
    A hash code for this chronology.
    The default implementation is based on the ID and class. Subclasses should add any additional state that they store.
    
    Overrides:
    
    hashCode in class java.lang.Object
    
    Returns:
    a suitable hash code
  - toString
```
public java.lang.String toString()
```
    Outputs this chronology as a String, using the ID.
    
    Overrides:
    
    toString in class java.lang.Object
    
    Returns:
    a string representation of this chronology, not null

Class Chronology

Specification for implementors

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

FROM

Constructor Detail

Chronology

Method Detail

from

ofLocale

of

getAvailableChronologies

getId

getCalendarType

date

date

dateYearDay

dateYearDay

dateEpochDay

date

dateNow

dateNow

dateNow

localDateTime

zonedDateTime

zonedDateTime

period

isLeapYear

prolepticYear

eraOf

eras

range

getDisplayName

resolveDate

compareTo

equals

hashCode

toString