Class TemporalQueries
TemporalQuery.
This class provides common implementations of TemporalQuery.
These are defined here as they must be constants, and the definition
of lambdas does not guarantee that. By assigning them once here,
they become 'normal' Java constants.
Queries are a key tool for extracting information from temporal objects. They exist to externalize the process of querying, permitting different approaches, as per the strategy design pattern. Examples might be a query that checks if the date is the day before February 29th in a leap year, or calculates the number of days to your next birthday.
The TemporalField interface provides another mechanism for querying
temporal objects. That interface is limited to returning a long.
By contrast, queries can return any type.
There are two equivalent ways of using a TemporalQuery.
The first is to invoke the method on this interface directly.
The second is to use TemporalAccessor.query(TemporalQuery):
// these two lines are equivalent, but the second approach is recommended temporal = thisQuery.queryFrom(temporal); temporal = temporal.query(thisQuery);It is recommended to use the second approach,
query(TemporalQuery),
as it is a lot clearer to read in code.
The most common implementations are method references, such as
LocalDate::from and ZoneId::from.
Additional common queries are provided to return:
- a Chronology,
- a LocalDate,
- a LocalTime,
- a ZoneOffset,
- a precision,
- a zone, or
- a zoneId.
- Since:
- 1.8
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Method Summary
Modifier and TypeMethodDescriptionstatic TemporalQuery<Chronology> A query for theChronology.static TemporalQuery<LocalDate> A query forLocalDatereturning null if not found.static TemporalQuery<LocalTime> A query forLocalTimereturning null if not found.static TemporalQuery<ZoneOffset> offset()A query forZoneOffsetreturning null if not found.static TemporalQuery<TemporalUnit> A query for the smallest supported unit.static TemporalQuery<ZoneId> zone()A lenient query for theZoneId, falling back to theZoneOffset.static TemporalQuery<ZoneId> zoneId()A strict query for theZoneId.
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Method Details
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zoneId
A strict query for theZoneId.This queries a
TemporalAccessorfor the zone. The zone is only returned if the date-time conceptually contains aZoneId. It will not be returned if the date-time only conceptually has anZoneOffset. Thus aZonedDateTimewill return the result ofgetZone(), but anOffsetDateTimewill return null.In most cases, applications should use
zone()as this query is too strict.The result from JDK classes implementing
TemporalAccessoris as follows:
LocalDatereturns null
LocalTimereturns null
LocalDateTimereturns null
ZonedDateTimereturns the associated zone
OffsetTimereturns null
OffsetDateTimereturns null
ChronoLocalDatereturns null
ChronoLocalDateTimereturns null
ChronoZonedDateTimereturns the associated zone
Erareturns null
DayOfWeekreturns null
Monthreturns null
Yearreturns null
YearMonthreturns null
MonthDayreturns null
ZoneOffsetreturns null
Instantreturns null- Returns:
- a query that can obtain the zone ID of a temporal, not null
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chronology
A query for theChronology.This queries a
TemporalAccessorfor the chronology. If the targetTemporalAccessorrepresents a date, or part of a date, then it should return the chronology that the date is expressed in. As a result of this definition, objects only representing time, such asLocalTime, will return null.The result from JDK classes implementing
TemporalAccessoris as follows:
LocalDatereturnsIsoChronology.INSTANCE
LocalTimereturns null (does not represent a date)
LocalDateTimereturnsIsoChronology.INSTANCE
ZonedDateTimereturnsIsoChronology.INSTANCE
OffsetTimereturns null (does not represent a date)
OffsetDateTimereturnsIsoChronology.INSTANCE
ChronoLocalDatereturns the associated chronology
ChronoLocalDateTimereturns the associated chronology
ChronoZonedDateTimereturns the associated chronology
Erareturns the associated chronology
DayOfWeekreturns null (shared across chronologies)
MonthreturnsIsoChronology.INSTANCE
YearreturnsIsoChronology.INSTANCE
YearMonthreturnsIsoChronology.INSTANCE
MonthDayreturns nullIsoChronology.INSTANCE
ZoneOffsetreturns null (does not represent a date)
Instantreturns null (does not represent a date)
The method
Chronology.from(TemporalAccessor)can be used as aTemporalQueryvia a method reference,Chronology::from. That method is equivalent to this query, except that it throws an exception if a chronology cannot be obtained.- Returns:
- a query that can obtain the chronology of a temporal, not null
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precision
A query for the smallest supported unit.This queries a
TemporalAccessorfor the time precision. If the targetTemporalAccessorrepresents a consistent or complete date-time, date or time then this must return the smallest precision actually supported. Note that fields such asNANO_OF_DAYandNANO_OF_SECONDare defined to always return ignoring the precision, thus this is the only way to find the actual smallest supported unit. For example, wereGregorianCalendarto implementTemporalAccessorit would return a precision ofMILLIS.The result from JDK classes implementing
TemporalAccessoris as follows:
LocalDatereturnsDAYS
LocalTimereturnsNANOS
LocalDateTimereturnsNANOS
ZonedDateTimereturnsNANOS
OffsetTimereturnsNANOS
OffsetDateTimereturnsNANOS
ChronoLocalDatereturnsDAYS
ChronoLocalDateTimereturnsNANOS
ChronoZonedDateTimereturnsNANOS
ErareturnsERAS
DayOfWeekreturnsDAYS
MonthreturnsMONTHS
YearreturnsYEARS
YearMonthreturnsMONTHS
MonthDayreturns null (does not represent a complete date or time)
ZoneOffsetreturns null (does not represent a date or time)
InstantreturnsNANOS- Returns:
- a query that can obtain the precision of a temporal, not null
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zone
A lenient query for theZoneId, falling back to theZoneOffset.This queries a
TemporalAccessorfor the zone. It first tries to obtain the zone, usingzoneId(). If that is not found it tries to obtain theoffset(). Thus aZonedDateTimewill return the result ofgetZone(), while anOffsetDateTimewill return the result ofgetOffset().In most cases, applications should use this query rather than
#zoneId().The method
ZoneId.from(TemporalAccessor)can be used as aTemporalQueryvia a method reference,ZoneId::from. That method is equivalent to this query, except that it throws an exception if a zone cannot be obtained.- Returns:
- a query that can obtain the zone ID or offset of a temporal, not null
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offset
A query forZoneOffsetreturning null if not found.This returns a
TemporalQuerythat can be used to query a temporal object for the offset. The query will return null if the temporal object cannot supply an offset.The query implementation examines the
OFFSET_SECONDSfield and uses it to create aZoneOffset.The method
ZoneOffset.from(TemporalAccessor)can be used as aTemporalQueryvia a method reference,ZoneOffset::from. This query andZoneOffset::fromwill return the same result if the temporal object contains an offset. If the temporal object does not contain an offset, then the method reference will throw an exception, whereas this query will return null.- Returns:
- a query that can obtain the offset of a temporal, not null
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localDate
A query forLocalDatereturning null if not found.This returns a
TemporalQuerythat can be used to query a temporal object for the local date. The query will return null if the temporal object cannot supply a local date.The query implementation examines the
EPOCH_DAYfield and uses it to create aLocalDate.The method
LocalDate.from(TemporalAccessor)can be used as aTemporalQueryvia a method reference,LocalDate::from. This query andLocalDate::fromwill return the same result if the temporal object contains a date. If the temporal object does not contain a date, then the method reference will throw an exception, whereas this query will return null.- Returns:
- a query that can obtain the date of a temporal, not null
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localTime
A query forLocalTimereturning null if not found.This returns a
TemporalQuerythat can be used to query a temporal object for the local time. The query will return null if the temporal object cannot supply a local time.The query implementation examines the
NANO_OF_DAYfield and uses it to create aLocalTime.The method
LocalTime.from(TemporalAccessor)can be used as aTemporalQueryvia a method reference,LocalTime::from. This query andLocalTime::fromwill return the same result if the temporal object contains a time. If the temporal object does not contain a time, then the method reference will throw an exception, whereas this query will return null.- Returns:
- a query that can obtain the time of a temporal, not null
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