https://openjdk.java.net/ 
/*
 * Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

/*
 * This file is available under and governed by the GNU General Public
 * License version 2 only, as published by the Free Software Foundation.
 * However, the following notice accompanied the original version of this
 * file:
 *
 * Copyright (c) 2012, Stephen Colebourne & Michael Nascimento Santos
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *  * Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 *
 *  * Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 *  * Neither the name of JSR-310 nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
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 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<Object>): 
  // 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 as static methods in TemporalQueries. 
Type parameters:
  • <R> – the type returned from the query
Implementation Requirements:
This interface places no restrictions on the mutability of implementations,
however immutability is strongly recommended.
Since:1.8
/**
 * Strategy for querying a temporal object.
 * <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 as static methods in {@link TemporalQueries}.
 *
 * @implSpec
 * This interface places no restrictions on the mutability of implementations,
 * however immutability is strongly recommended.
 *
 * @param <R> the type returned from the query
 *
 * @since 1.8
 */
@FunctionalInterface
public interface TemporalQuery<R> {

    
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 TemporalAccessor.query(TemporalQuery<Object>): 
  // 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. 
Params:
  • temporal –  the temporal object to query, not null
Throws:
Implementation Requirements: 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 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 querying the chronology. 

This method may be called from multiple threads in parallel.
It must be thread-safe when invoked.
Returns:the queried value, may return null to indicate not found
/**
     * Queries the specified temporal object.
     * <p>
     * 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.
     * <p>
     * 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)}:
     * <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.
     *
     * @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.
     * <p>
     * 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}.
     * <p>
     * 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);

}