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* 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 = new TemporalQuery<>() {
@Override
public ZoneId queryFrom(TemporalAccessor temporal) {
return temporal.query(TemporalQueries.ZONE_ID);
}
@Override
public String toString() {
return "ZoneId";
}
};
/**
* A query for the {@code Chronology}.
*/
static final TemporalQuery<Chronology> CHRONO = new TemporalQuery<>() {
@Override
public Chronology queryFrom(TemporalAccessor temporal) {
return temporal.query(TemporalQueries.CHRONO);
}
@Override
public String toString() {
return "Chronology";
}
};
/**
* A query for the smallest supported unit.
*/
static final TemporalQuery<TemporalUnit> PRECISION = new TemporalQuery<>() {
@Override
public TemporalUnit queryFrom(TemporalAccessor temporal) {
return temporal.query(TemporalQueries.PRECISION);
}
@Override
public String toString() {
return "Precision";
}
};
//-----------------------------------------------------------------------
/**
* A query for {@code ZoneOffset} returning null if not found.
*/
static final TemporalQuery<ZoneOffset> OFFSET = new TemporalQuery<>() {
@Override
public ZoneOffset queryFrom(TemporalAccessor temporal) {
if (temporal.isSupported(OFFSET_SECONDS)) {
return ZoneOffset.ofTotalSeconds(temporal.get(OFFSET_SECONDS));
}
return null;
}
@Override
public String toString() {
return "ZoneOffset";
}
};
/**
* A lenient query for the {@code ZoneId}, falling back to the {@code ZoneOffset}.
*/
static final TemporalQuery<ZoneId> ZONE = new TemporalQuery<>() {
@Override
public ZoneId queryFrom(TemporalAccessor temporal) {
ZoneId zone = temporal.query(ZONE_ID);
return (zone != null ? zone : temporal.query(OFFSET));
}
@Override
public String toString() {
return "Zone";
}
};
/**
* A query for {@code LocalDate} returning null if not found.
*/
static final TemporalQuery<LocalDate> LOCAL_DATE = new TemporalQuery<>() {
@Override
public LocalDate queryFrom(TemporalAccessor temporal) {
if (temporal.isSupported(EPOCH_DAY)) {
return LocalDate.ofEpochDay(temporal.getLong(EPOCH_DAY));
}
return null;
}
@Override
public String toString() {
return "LocalDate";
}
};
/**
* A query for {@code LocalTime} returning null if not found.
*/
static final TemporalQuery<LocalTime> LOCAL_TIME = new TemporalQuery<>() {
@Override
public LocalTime queryFrom(TemporalAccessor temporal) {
if (temporal.isSupported(NANO_OF_DAY)) {
return LocalTime.ofNanoOfDay(temporal.getLong(NANO_OF_DAY));
}
return null;
}
@Override
public String toString() {
return "LocalTime";
}
};
}