public final class TemporalQueries extends Object
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
-
Method Summary
Modifier and TypeMethodDescriptionstatic TemporalQuery<Chronology>
A query for theChronology
.static TemporalQuery<LocalDate>
A query forLocalDate
returning null if not found.static TemporalQuery<LocalTime>
A query forLocalTime
returning null if not found.static TemporalQuery<ZoneOffset>
offset()
A query forZoneOffset
returning 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
.
-
Method Details
-
zoneId
A strict query for theZoneId
.This queries a
TemporalAccessor
for 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 aZonedDateTime
will return the result ofgetZone()
, but anOffsetDateTime
will return null.In most cases, applications should use
zone()
as this query is too strict.The result from JDK classes implementing
TemporalAccessor
is as follows:
LocalDate
returns null
LocalTime
returns null
LocalDateTime
returns null
ZonedDateTime
returns the associated zone
OffsetTime
returns null
OffsetDateTime
returns null
ChronoLocalDate
returns null
ChronoLocalDateTime
returns null
ChronoZonedDateTime
returns the associated zone
Era
returns null
DayOfWeek
returns null
Month
returns null
Year
returns null
YearMonth
returns null
MonthDay
returns null
ZoneOffset
returns null
Instant
returns null- Returns:
- a query that can obtain the zone ID of a temporal, not null
-
chronology
A query for theChronology
.This queries a
TemporalAccessor
for the chronology. If the targetTemporalAccessor
represents 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
TemporalAccessor
is as follows:
LocalDate
returnsIsoChronology.INSTANCE
LocalTime
returns null (does not represent a date)
LocalDateTime
returnsIsoChronology.INSTANCE
ZonedDateTime
returnsIsoChronology.INSTANCE
OffsetTime
returns null (does not represent a date)
OffsetDateTime
returnsIsoChronology.INSTANCE
ChronoLocalDate
returns the associated chronology
ChronoLocalDateTime
returns the associated chronology
ChronoZonedDateTime
returns the associated chronology
Era
returns the associated chronology
DayOfWeek
returns null (shared across chronologies)
Month
returnsIsoChronology.INSTANCE
Year
returnsIsoChronology.INSTANCE
YearMonth
returnsIsoChronology.INSTANCE
MonthDay
returns nullIsoChronology.INSTANCE
ZoneOffset
returns null (does not represent a date)
Instant
returns null (does not represent a date)
The method
Chronology.from(TemporalAccessor)
can be used as aTemporalQuery
via 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
-
precision
A query for the smallest supported unit.This queries a
TemporalAccessor
for the time precision. If the targetTemporalAccessor
represents a consistent or complete date-time, date or time then this must return the smallest precision actually supported. Note that fields such asNANO_OF_DAY
andNANO_OF_SECOND
are defined to always return ignoring the precision, thus this is the only way to find the actual smallest supported unit. For example, wereGregorianCalendar
to implementTemporalAccessor
it would return a precision ofMILLIS
.The result from JDK classes implementing
TemporalAccessor
is as follows:
LocalDate
returnsDAYS
LocalTime
returnsNANOS
LocalDateTime
returnsNANOS
ZonedDateTime
returnsNANOS
OffsetTime
returnsNANOS
OffsetDateTime
returnsNANOS
ChronoLocalDate
returnsDAYS
ChronoLocalDateTime
returnsNANOS
ChronoZonedDateTime
returnsNANOS
Era
returnsERAS
DayOfWeek
returnsDAYS
Month
returnsMONTHS
Year
returnsYEARS
YearMonth
returnsMONTHS
MonthDay
returns null (does not represent a complete date or time)
ZoneOffset
returns null (does not represent a date or time)
Instant
returnsNANOS
- Returns:
- a query that can obtain the precision of a temporal, not null
-
zone
A lenient query for theZoneId
, falling back to theZoneOffset
.This queries a
TemporalAccessor
for the zone. It first tries to obtain the zone, usingzoneId()
. If that is not found it tries to obtain theoffset()
. Thus aZonedDateTime
will return the result ofgetZone()
, while anOffsetDateTime
will return the result ofgetOffset()
.In most cases, applications should use this query rather than
#zoneId()
.The method
ZoneId.from(TemporalAccessor)
can be used as aTemporalQuery
via 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
-
offset
A query forZoneOffset
returning null if not found.This returns a
TemporalQuery
that 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_SECONDS
field and uses it to create aZoneOffset
.The method
ZoneOffset.from(TemporalAccessor)
can be used as aTemporalQuery
via a method reference,ZoneOffset::from
. This query andZoneOffset::from
will 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
-
localDate
A query forLocalDate
returning null if not found.This returns a
TemporalQuery
that 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_DAY
field and uses it to create aLocalDate
.The method
ZoneOffset.from(TemporalAccessor)
can be used as aTemporalQuery
via a method reference,LocalDate::from
. This query andLocalDate::from
will 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
-
localTime
A query forLocalTime
returning null if not found.This returns a
TemporalQuery
that 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_DAY
field and uses it to create aLocalTime
.The method
ZoneOffset.from(TemporalAccessor)
can be used as aTemporalQuery
via a method reference,LocalTime::from
. This query andLocalTime::from
will 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
-