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 * file:

 *

 * Copyright (c) 2007-2012, Stephen Colebourne & Michael Nascimento Santos

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package java.time.temporal;

import static java.time.temporal.ChronoField.EPOCH_DAY;

import static java.time.temporal.ChronoField.NANO_OF_DAY;

import static java.time.temporal.ChronoField.OFFSET_SECONDS;

import java.time.LocalDate;

import java.time.LocalTime;

import java.time.ZoneId;

import java.time.ZoneOffset;

import java.time.chrono.Chronology;

/**

 * Common implementations of {@code TemporalQuery}.

 * <p>

 * This class provides common implementations of {@link 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.

 * <p>

 * 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.

 * <p>

 * The {@link TemporalField} interface provides another mechanism for querying

 * temporal objects. That interface is limited to returning a {@code long}.

 * By contrast, queries can return any type.

 * <p>

 * There are two equivalent ways of using a {@code TemporalQuery}.

 * The first is to invoke the method on this interface directly.

 * The second is to use {@link TemporalAccessor#query(TemporalQuery)}:

 * <pre>

 *   // these two lines are equivalent, but the second approach is recommended

 *   temporal = thisQuery.queryFrom(temporal);

 *   temporal = temporal.query(thisQuery);

 * </pre>

 * It is recommended to use the second approach, {@code query(TemporalQuery)},

 * as it is a lot clearer to read in code.

 * <p>

 * The most common implementations are method references, such as

 * {@code LocalDate::from} and {@code ZoneId::from}.

 * Additional common queries are provided to return:

 * <ul>

 * <li> a Chronology,

 * <li> a LocalDate,

 * <li> a LocalTime,

 * <li> a ZoneOffset,

 * <li> a precision,

 * <li> a zone, or

 * <li> a zoneId.

 * </ul>

 *

 * @since 1.8

 */

public final class TemporalQueries {

    // note that it is vital that each method supplies a constant, not a

    // calculated value, as they will be checked for using ==

    // it is also vital that each constant is different (due to the == checking)

    // as such, alterations to this code must be done with care

    /**

     * Private constructor since this is a utility class.

     */

    private TemporalQueries() {

    }

    //-----------------------------------------------------------------------

    // special constants should be used to extract information from a TemporalAccessor

    // that cannot be derived in other ways

    // Javadoc added here, so as to pretend they are more normal than they really are

    /**

     * A strict query for the {@code ZoneId}.

     * <p>

     * This queries a {@code TemporalAccessor} for the zone.

     * The zone is only returned if the date-time conceptually contains a {@code ZoneId}.

     * It will not be returned if the date-time only conceptually has an {@code ZoneOffset}.

     * Thus a {@link java.time.ZonedDateTime} will return the result of {@code getZone()},

     * but an {@link java.time.OffsetDateTime} will return null.

     * <p>

     * In most cases, applications should use {@link #zone()} as this query is too strict.

     * <p>

     * The result from JDK classes implementing {@code TemporalAccessor} is as follows:<br>

     * {@code LocalDate} returns null<br>

     * {@code LocalTime} returns null<br>

     * {@code LocalDateTime} returns null<br>

     * {@code ZonedDateTime} returns the associated zone<br>

     * {@code OffsetTime} returns null<br>

     * {@code OffsetDateTime} returns null<br>

     * {@code ChronoLocalDate} returns null<br>

     * {@code ChronoLocalDateTime} returns null<br>

     * {@code ChronoZonedDateTime} returns the associated zone<br>

     * {@code Era} returns null<br>

     * {@code DayOfWeek} returns null<br>

     * {@code Month} returns null<br>

     * {@code Year} returns null<br>

     * {@code YearMonth} returns null<br>

     * {@code MonthDay} returns null<br>

     * {@code ZoneOffset} returns null<br>

     * {@code Instant} returns null<br>

     *

     * @return a query that can obtain the zone ID of a temporal, not null

     */

    public static TemporalQuery<ZoneId> zoneId() {

        return TemporalQueries.ZONE_ID;

    }

    /**

     * A query for the {@code Chronology}.

     * <p>

     * This queries a {@code TemporalAccessor} for the chronology.

     * If the target {@code 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

     * {@code LocalTime}, will return null.

     * <p>

     * The result from JDK classes implementing {@code TemporalAccessor} is as follows:<br>

     * {@code LocalDate} returns {@code IsoChronology.INSTANCE}<br>

     * {@code LocalTime} returns null (does not represent a date)<br>

     * {@code LocalDateTime} returns {@code IsoChronology.INSTANCE}<br>

     * {@code ZonedDateTime} returns {@code IsoChronology.INSTANCE}<br>

     * {@code OffsetTime} returns null (does not represent a date)<br>

     * {@code OffsetDateTime} returns {@code IsoChronology.INSTANCE}<br>

     * {@code ChronoLocalDate} returns the associated chronology<br>

     * {@code ChronoLocalDateTime} returns the associated chronology<br>

     * {@code ChronoZonedDateTime} returns the associated chronology<br>

     * {@code Era} returns the associated chronology<br>

     * {@code DayOfWeek} returns null (shared across chronologies)<br>

     * {@code Month} returns {@code IsoChronology.INSTANCE}<br>

     * {@code Year} returns {@code IsoChronology.INSTANCE}<br>

     * {@code YearMonth} returns {@code IsoChronology.INSTANCE}<br>

     * {@code MonthDay} returns null {@code IsoChronology.INSTANCE}<br>

     * {@code ZoneOffset} returns null (does not represent a date)<br>

     * {@code Instant} returns null (does not represent a date)<br>

     * <p>

     * The method {@link java.time.chrono.Chronology#from(TemporalAccessor)} can be used as a

     * {@code TemporalQuery} via a method reference, {@code Chronology::from}.

     * That method is equivalent to this query, except that it throws an

     * exception if a chronology cannot be obtained.

     *

     * @return a query that can obtain the chronology of a temporal, not null

     */

    public static TemporalQuery<Chronology> chronology() {

        return TemporalQueries.CHRONO;

    }

    /**

     * A query for the smallest supported unit.

     * <p>

     * This queries a {@code TemporalAccessor} for the time precision.

     * If the target {@code 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 {@code NANO_OF_DAY} and {@code 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 {@code GregorianCalendar} to implement {@code TemporalAccessor}

     * it would return a precision of {@code MILLIS}.

     * <p>

     * The result from JDK classes implementing {@code TemporalAccessor} is as follows:<br>

     * {@code LocalDate} returns {@code DAYS}<br>

     * {@code LocalTime} returns {@code NANOS}<br>

     * {@code LocalDateTime} returns {@code NANOS}<br>

     * {@code ZonedDateTime} returns {@code NANOS}<br>

     * {@code OffsetTime} returns {@code NANOS}<br>

     * {@code OffsetDateTime} returns {@code NANOS}<br>

     * {@code ChronoLocalDate} returns {@code DAYS}<br>

     * {@code ChronoLocalDateTime} returns {@code NANOS}<br>

     * {@code ChronoZonedDateTime} returns {@code NANOS}<br>

     * {@code Era} returns {@code ERAS}<br>

     * {@code DayOfWeek} returns {@code DAYS}<br>

     * {@code Month} returns {@code MONTHS}<br>

     * {@code Year} returns {@code YEARS}<br>

     * {@code YearMonth} returns {@code MONTHS}<br>

     * {@code MonthDay} returns null (does not represent a complete date or time)<br>

     * {@code ZoneOffset} returns null (does not represent a date or time)<br>

     * {@code Instant} returns {@code NANOS}<br>

     *

     * @return a query that can obtain the precision of a temporal, not null

     */

    public static TemporalQuery<TemporalUnit> precision() {

        return TemporalQueries.PRECISION;

    }

    //-----------------------------------------------------------------------

    // non-special constants are standard queries that derive information from other information

    /**

     * A lenient query for the {@code ZoneId}, falling back to the {@code ZoneOffset}.

     * <p>

     * This queries a {@code TemporalAccessor} for the zone.

     * It first tries to obtain the zone, using {@link #zoneId()}.

     * If that is not found it tries to obtain the {@link #offset()}.

     * Thus a {@link java.time.ZonedDateTime} will return the result of {@code getZone()},

     * while an {@link java.time.OffsetDateTime} will return the result of {@code getOffset()}.

     * <p>

     * In most cases, applications should use this query rather than {@code #zoneId()}.

     * <p>

     * The method {@link ZoneId#from(TemporalAccessor)} can be used as a

     * {@code TemporalQuery} via a method reference, {@code ZoneId::from}.

     * That method is equivalent to this query, except that it throws an

     * exception if a zone cannot be obtained.

     *

     * @return a query that can obtain the zone ID or offset of a temporal, not null

     */

    public static TemporalQuery<ZoneId> zone() {

        return TemporalQueries.ZONE;

    }

    /**

     * A query for {@code ZoneOffset} returning null if not found.

     * <p>

     * This returns a {@code 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.

     * <p>

     * The query implementation examines the {@link ChronoField#OFFSET_SECONDS OFFSET_SECONDS}

     * field and uses it to create a {@code ZoneOffset}.

     * <p>

     * The method {@link java.time.ZoneOffset#from(TemporalAccessor)} can be used as a

     * {@code TemporalQuery} via a method reference, {@code ZoneOffset::from}.

     * This query and {@code 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 a query that can obtain the offset of a temporal, not null

     */

    public static TemporalQuery<ZoneOffset> offset() {

        return TemporalQueries.OFFSET;

    }

    /**

     * A query for {@code LocalDate} returning null if not found.

     * <p>

     * This returns a {@code 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.

     * <p>

     * The query implementation examines the {@link ChronoField#EPOCH_DAY EPOCH_DAY}

     * field and uses it to create a {@code LocalDate}.

     * <p>

     * The method {@link ZoneOffset#from(TemporalAccessor)} can be used as a

     * {@code TemporalQuery} via a method reference, {@code LocalDate::from}.

     * This query and {@code 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 a query that can obtain the date of a temporal, not null

     */

    public static TemporalQuery<LocalDate> localDate() {

        return TemporalQueries.LOCAL_DATE;

    }

    /**

     * A query for {@code LocalTime} returning null if not found.

     * <p>

     * This returns a {@code 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.

     * <p>

     * The query implementation examines the {@link ChronoField#NANO_OF_DAY NANO_OF_DAY}

     * field and uses it to create a {@code LocalTime}.

     * <p>

     * The method {@link ZoneOffset#from(TemporalAccessor)} can be used as a

     * {@code TemporalQuery} via a method reference, {@code LocalTime::from}.

     * This query and {@code 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 a query that can obtain the time of a temporal, not null

     */

    public static TemporalQuery<LocalTime> localTime() {

        return TemporalQueries.LOCAL_TIME;

    }

    //-----------------------------------------------------------------------

    /**

     * A strict query for the {@code ZoneId}.

     */

    static final TemporalQuery<ZoneId> ZONE_ID = (temporal) ->

        temporal.query(TemporalQueries.ZONE_ID);

    /**

     * A query for the {@code Chronology}.

     */

    static final TemporalQuery<Chronology> CHRONO = (temporal) ->

        temporal.query(TemporalQueries.CHRONO);

    /**

     * A query for the smallest supported unit.

     */

    static final TemporalQuery<TemporalUnit> PRECISION = (temporal) ->

        temporal.query(TemporalQueries.PRECISION);

    //-----------------------------------------------------------------------

    /**

     * A query for {@code ZoneOffset} returning null if not found.

     */

    static final TemporalQuery<ZoneOffset> OFFSET = (temporal) -> {

        if (temporal.isSupported(OFFSET_SECONDS)) {

            return ZoneOffset.ofTotalSeconds(temporal.get(OFFSET_SECONDS));

        }

        return null;

    };

    /**

     * A lenient query for the {@code ZoneId}, falling back to the {@code ZoneOffset}.

     */

    static final TemporalQuery<ZoneId> ZONE = (temporal) -> {

        ZoneId zone = temporal.query(ZONE_ID);

        return (zone != null ? zone : temporal.query(OFFSET));

    };

    /**

     * A query for {@code LocalDate} returning null if not found.

     */

    static final TemporalQuery<LocalDate> LOCAL_DATE = (temporal) -> {

        if (temporal.isSupported(EPOCH_DAY)) {

            return LocalDate.ofEpochDay(temporal.getLong(EPOCH_DAY));

        }

        return null;

    };

    /**

     * A query for {@code LocalTime} returning null if not found.

     */

    static final TemporalQuery<LocalTime> LOCAL_TIME = (temporal) -> {

        if (temporal.isSupported(NANO_OF_DAY)) {

            return LocalTime.ofNanoOfDay(temporal.getLong(NANO_OF_DAY));

        }

        return null;

    };

}