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* Copyright (c) 2012, Stephen Colebourne & Michael Nascimento Santos
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package java.time.temporal;
import java.time.DateTimeException;
/**
* Strategy for querying a temporal object.
*
* 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 {@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.
*
* 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)}:
*
* // 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, {@code query(TemporalQuery)},
* as it is a lot clearer to read in code.
*
* The most common implementations are method references, such as
* {@code LocalDate::from} and {@code ZoneId::from}.
* Additional common queries are provided as static methods in {@link TemporalQueries}.
*
* @implSpec
* This interface places no restrictions on the mutability of implementations,
* however immutability is strongly recommended.
*
* @param the type returned from the query
*
* @since 1.8
*/
@FunctionalInterface
public interface TemporalQuery {
/**
* Queries the specified temporal object.
*
* This queries the specified temporal object to return an object using the logic
* encapsulated in the implementing class.
* 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.
*
* There are two equivalent ways of using this method.
* The first is to invoke this method directly.
* The second is to use {@link 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, {@code query(TemporalQuery)},
* as it is a lot clearer to read in code.
*
* @implSpec
* The implementation must take the input object and query it.
* The implementation defines the logic of the query and is responsible for
* documenting that logic.
* It may use any method on {@code TemporalAccessor} to determine the result.
* The input object must not be altered.
*
* The input temporal object may be in a calendar system other than ISO.
* Implementations may choose to document compatibility with other calendar systems,
* or reject non-ISO temporal objects by {@link TemporalQueries#chronology() querying the chronology}.
*
* This method may be called from multiple threads in parallel.
* It must be thread-safe when invoked.
*
* @param temporal the temporal object to query, not null
* @return the queried value, may return null to indicate not found
* @throws DateTimeException if unable to query
* @throws ArithmeticException if numeric overflow occurs
*/
R queryFrom(TemporalAccessor temporal);
}