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Java Standard Edition (SE)

TemporalQueries


compact1, compact2, compact3
java.time.temporal

Class TemporalQueries



  • public final class TemporalQueries
    extends Object
    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.
    Since:
    1.8
    • Method Detail

      • zoneId

        public static TemporalQuery<ZoneId> 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 ZonedDateTime will return the result of getZone(), but an 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

        Returns:
        a query that can obtain the zone ID of a temporal, not null
      • chronology

        public static TemporalQuery<Chronology> 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 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.

        Returns:
        a query that can obtain the chronology of a temporal, not null
      • precision

        public static TemporalQuery<TemporalUnit> precision()
        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

        Returns:
        a query that can obtain the precision of a temporal, not null
      • zone

        public static TemporalQuery<ZoneId> zone()
        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 ZonedDateTime will return the result of getZone(), while an 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.

        Returns:
        a query that can obtain the zone ID or offset of a temporal, not null
      • offset

        public static TemporalQuery<ZoneOffset> offset()
        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 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.

        Returns:
        a query that can obtain the offset of a temporal, not null
      • localDate

        public static TemporalQuery<LocalDate> 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.

        Returns:
        a query that can obtain the date of a temporal, not null
      • localTime

        public static TemporalQuery<LocalTime> 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.

        Returns:
        a query that can obtain the time of a temporal, not null


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