TemporalQueries
class TemporalQueries
kotlin.Any | |
↳ | java.time.temporal.TemporalQueries |
Common implementations of 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.
Summary
Public methods | |
---|---|
static TemporalQuery<Chronology!>! |
A query for the |
static TemporalQuery<LocalDate!>! |
A query for |
static TemporalQuery<LocalTime!>! |
A query for |
static TemporalQuery<ZoneOffset!>! |
offset() A query for |
static TemporalQuery<TemporalUnit!>! |
A query for the smallest supported unit. |
static TemporalQuery<ZoneId!>! |
zone() A lenient query for the |
static TemporalQuery<ZoneId!>! |
zoneId() A strict query for the |
Public methods
chronology
static fun chronology(): TemporalQuery<Chronology!>!
A query for the Chronology
.
This queries a TemporalAccessor
for the chronology. If the target TemporalAccessor
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 as LocalTime
, will return null.
The result from JDK classes implementing TemporalAccessor
is as follows:
LocalDate
returns IsoChronology.INSTANCE
LocalTime
returns null (does not represent a date)
LocalDateTime
returns IsoChronology.INSTANCE
ZonedDateTime
returns IsoChronology.INSTANCE
OffsetTime
returns null (does not represent a date)
OffsetDateTime
returns IsoChronology.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
returns IsoChronology.INSTANCE
Year
returns IsoChronology.INSTANCE
YearMonth
returns IsoChronology.INSTANCE
MonthDay
returns null IsoChronology.INSTANCE
ZoneOffset
returns null (does not represent a date)
Instant
returns null (does not represent a date)
The method java.time.chrono.Chronology#from(TemporalAccessor)
can be used as a TemporalQuery
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.
Return | |
---|---|
TemporalQuery<Chronology!>! |
a query that can obtain the chronology of a temporal, not null |
localDate
static fun localDate(): TemporalQuery<LocalDate!>!
A query for LocalDate
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 a LocalDate
.
The method ZoneOffset#from(TemporalAccessor)
can be used as a TemporalQuery
via a method reference, LocalDate::from
. This query and LocalDate::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.
Return | |
---|---|
TemporalQuery<LocalDate!>! |
a query that can obtain the date of a temporal, not null |
localTime
static fun localTime(): TemporalQuery<LocalTime!>!
A query for LocalTime
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 a LocalTime
.
The method ZoneOffset#from(TemporalAccessor)
can be used as a TemporalQuery
via a method reference, LocalTime::from
. This query and LocalTime::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.
Return | |
---|---|
TemporalQuery<LocalTime!>! |
a query that can obtain the time of a temporal, not null |
offset
static fun offset(): TemporalQuery<ZoneOffset!>!
A query for ZoneOffset
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 a ZoneOffset
.
The method java.time.ZoneOffset#from(TemporalAccessor)
can be used as a TemporalQuery
via a method reference, ZoneOffset::from
. This query and ZoneOffset::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.
Return | |
---|---|
TemporalQuery<ZoneOffset!>! |
a query that can obtain the offset of a temporal, not null |
precision
static fun precision(): TemporalQuery<TemporalUnit!>!
A query for the smallest supported unit.
This queries a TemporalAccessor
for the time precision. If the target TemporalAccessor
represents a consistent or complete date-time, date or time then this must return the smallest precision actually supported. Note that fields such as NANO_OF_DAY
and NANO_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, were GregorianCalendar
to implement TemporalAccessor
it would return a precision of MILLIS
.
The result from JDK classes implementing TemporalAccessor
is as follows:
LocalDate
returns DAYS
LocalTime
returns NANOS
LocalDateTime
returns NANOS
ZonedDateTime
returns NANOS
OffsetTime
returns NANOS
OffsetDateTime
returns NANOS
ChronoLocalDate
returns DAYS
ChronoLocalDateTime
returns NANOS
ChronoZonedDateTime
returns NANOS
Era
returns ERAS
DayOfWeek
returns DAYS
Month
returns MONTHS
Year
returns YEARS
YearMonth
returns MONTHS
MonthDay
returns null (does not represent a complete date or time)
ZoneOffset
returns null (does not represent a date or time)
Instant
returns NANOS
Return | |
---|---|
TemporalQuery<TemporalUnit!>! |
a query that can obtain the precision of a temporal, not null |
zone
static fun zone(): TemporalQuery<ZoneId!>!
A lenient query for the ZoneId
, falling back to the ZoneOffset
.
This queries a TemporalAccessor
for the zone. It first tries to obtain the zone, using zoneId()
. If that is not found it tries to obtain the offset()
. Thus a java.time.ZonedDateTime
will return the result of getZone()
, while an java.time.OffsetDateTime
will return the result of getOffset()
.
In most cases, applications should use this query rather than zoneId()
.
The method ZoneId#from(TemporalAccessor)
can be used as a TemporalQuery
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.
Return | |
---|---|
TemporalQuery<ZoneId!>! |
a query that can obtain the zone ID or offset of a temporal, not null |
zoneId
static fun zoneId(): TemporalQuery<ZoneId!>!
A strict query for the ZoneId
.
This queries a TemporalAccessor
for the zone. The zone is only returned if the date-time conceptually contains a ZoneId
. It will not be returned if the date-time only conceptually has an ZoneOffset
. Thus a java.time.ZonedDateTime
will return the result of getZone()
, but an java.time.OffsetDateTime
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
Return | |
---|---|
TemporalQuery<ZoneId!>! |
a query that can obtain the zone ID of a temporal, not null |