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;
import java.time.Duration;
import java.time.LocalTime;
import java.time.Period;
import java.time.chrono.ChronoLocalDate;
import java.time.chrono.ChronoLocalDateTime;
import java.time.chrono.ChronoZonedDateTime;


A unit of date-time, such as Days or Hours.


Measurement of time is built on units, such as years, months, days, hours, minutes and seconds.
Implementations of this interface represent those units.

 An instance of this interface represents the unit itself, rather than an amount of the unit. See Period for a class that represents an amount in terms of the common units. 
 The most commonly used units are defined in ChronoUnit. Further units are supplied in IsoFields. Units can also be written by application code by implementing this interface. 
 The unit works using double dispatch. Client code calls methods on a date-time like LocalDateTime which check if the unit is a ChronoUnit. If it is, then the date-time must handle it. Otherwise, the method call is re-dispatched to the matching method in this interface. 
Implementation Requirements:
This interface must be implemented with care to ensure other classes operate correctly.
All implementations that can be instantiated must be final, immutable and thread-safe.
It is recommended to use an enum where possible.
Since:1.8
/**
 * A unit of date-time, such as Days or Hours.
 * <p>
 * Measurement of time is built on units, such as years, months, days, hours, minutes and seconds.
 * Implementations of this interface represent those units.
 * <p>
 * An instance of this interface represents the unit itself, rather than an amount of the unit.
 * See {@link Period} for a class that represents an amount in terms of the common units.
 * <p>
 * The most commonly used units are defined in {@link ChronoUnit}.
 * Further units are supplied in {@link IsoFields}.
 * Units can also be written by application code by implementing this interface.
 * <p>
 * The unit works using double dispatch. Client code calls methods on a date-time like
 * {@code LocalDateTime} which check if the unit is a {@code ChronoUnit}.
 * If it is, then the date-time must handle it.
 * Otherwise, the method call is re-dispatched to the matching method in this interface.
 *
 * @implSpec
 * This interface must be implemented with care to ensure other classes operate correctly.
 * All implementations that can be instantiated must be final, immutable and thread-safe.
 * It is recommended to use an enum where possible.
 *
 * @since 1.8
 */
public interface TemporalUnit {

    
Gets the duration of this unit, which may be an estimate.

 All units return a duration measured in standard nanoseconds from this method. The duration will be positive and non-zero. For example, an hour has a duration of 60 * 60 * 1,000,000,000ns. 
 Some units may return an accurate duration while others return an estimate. For example, days have an estimated duration due to the possibility of daylight saving time changes. To determine if the duration is an estimate, use isDurationEstimated(). 
Returns:the duration of this unit, which may be an estimate, not null
/**
     * Gets the duration of this unit, which may be an estimate.
     * <p>
     * All units return a duration measured in standard nanoseconds from this method.
     * The duration will be positive and non-zero.
     * For example, an hour has a duration of {@code 60 * 60 * 1,000,000,000ns}.
     * <p>
     * Some units may return an accurate duration while others return an estimate.
     * For example, days have an estimated duration due to the possibility of
     * daylight saving time changes.
     * To determine if the duration is an estimate, use {@link #isDurationEstimated()}.
     *
     * @return the duration of this unit, which may be an estimate, not null
     */
    Duration getDuration();

    
Checks if the duration of the unit is an estimate.


All units have a duration, however the duration is not always accurate.
For example, days have an estimated duration due to the possibility of
daylight saving time changes.
This method returns true if the duration is an estimate and false if it is
accurate. Note that accurate/estimated ignores leap seconds.

Returns:true if the duration is estimated, false if accurate
/**
     * Checks if the duration of the unit is an estimate.
     * <p>
     * All units have a duration, however the duration is not always accurate.
     * For example, days have an estimated duration due to the possibility of
     * daylight saving time changes.
     * This method returns true if the duration is an estimate and false if it is
     * accurate. Note that accurate/estimated ignores leap seconds.
     *
     * @return true if the duration is estimated, false if accurate
     */
    boolean isDurationEstimated();

    //-----------------------------------------------------------------------
    
Checks if this unit represents a component of a date.

 A date is time-based if it can be used to imply meaning from a date. It must have a duration that is an integral multiple of the length of a standard day. Note that it is valid for both isDateBased() and isTimeBased() to return false, such as when representing a unit like 36 hours. 
Returns:true if this unit is a component of a date
/**
     * Checks if this unit represents a component of a date.
     * <p>
     * A date is time-based if it can be used to imply meaning from a date.
     * It must have a {@linkplain #getDuration() duration} that is an integral
     * multiple of the length of a standard day.
     * Note that it is valid for both {@code isDateBased()} and {@code isTimeBased()}
     * to return false, such as when representing a unit like 36 hours.
     *
     * @return true if this unit is a component of a date
     */
    boolean isDateBased();

    
Checks if this unit represents a component of a time.

 A unit is time-based if it can be used to imply meaning from a time. It must have a duration that divides into the length of a standard day without remainder. Note that it is valid for both isDateBased() and isTimeBased() to return false, such as when representing a unit like 36 hours. 
Returns:true if this unit is a component of a time
/**
     * Checks if this unit represents a component of a time.
     * <p>
     * A unit is time-based if it can be used to imply meaning from a time.
     * It must have a {@linkplain #getDuration() duration} that divides into
     * the length of a standard day without remainder.
     * Note that it is valid for both {@code isDateBased()} and {@code isTimeBased()}
     * to return false, such as when representing a unit like 36 hours.
     *
     * @return true if this unit is a component of a time
     */
    boolean isTimeBased();

    //-----------------------------------------------------------------------
    
Checks if this unit is supported by the specified temporal object.


This checks that the implementing date-time can add/subtract this unit.
This can be used to avoid throwing an exception.

 This default implementation derives the value using Temporal.plus(long, TemporalUnit). 
Params:
  • temporal –  the temporal object to check, not null
Returns:true if the unit is supported
/**
     * Checks if this unit is supported by the specified temporal object.
     * <p>
     * This checks that the implementing date-time can add/subtract this unit.
     * This can be used to avoid throwing an exception.
     * <p>
     * This default implementation derives the value using
     * {@link Temporal#plus(long, TemporalUnit)}.
     *
     * @param temporal  the temporal object to check, not null
     * @return true if the unit is supported
     */
    default boolean isSupportedBy(Temporal temporal) {
        if (temporal instanceof LocalTime) {
            return isTimeBased();
        }
        if (temporal instanceof ChronoLocalDate) {
            return isDateBased();
        }
        if (temporal instanceof ChronoLocalDateTime || temporal instanceof ChronoZonedDateTime) {
            return true;
        }
        try {
            temporal.plus(1, this);
            return true;
        } catch (UnsupportedTemporalTypeException ex) {
            return false;
        } catch (RuntimeException ex) {
            try {
                temporal.plus(-1, this);
                return true;
            } catch (RuntimeException ex2) {
                return false;
            }
        }
    }

    
Returns a copy of the specified temporal object with the specified period added.


The period added is a multiple of this unit. For example, this method
could be used to add "3 days" to a date by calling this method on the
instance representing "days", passing the date and the period "3".
The period to be added may be negative, which is equivalent to subtraction.

 There are two equivalent ways of using this method. The first is to invoke this method directly. The second is to use Temporal.plus(long, TemporalUnit): 
  // these two lines are equivalent, but the second approach is recommended
  temporal = thisUnit.addTo(temporal);
  temporal = temporal.plus(thisUnit);

 It is recommended to use the second approach, plus(TemporalUnit), as it is a lot clearer to read in code. 
 Implementations should perform any queries or calculations using the units available in ChronoUnit or the fields available in ChronoField. If the unit is not supported an UnsupportedTemporalTypeException must be thrown. 

Implementations must not alter the specified temporal object.
Instead, an adjusted copy of the original must be returned.
This provides equivalent, safe behavior for immutable and mutable implementations.

Params:
  • temporal –  the temporal object to adjust, not null
  • amount –  the amount of this unit to add, positive or negative
Type parameters:
  • <R> –  the type of the Temporal object
Throws:
Returns:the adjusted temporal object, not null
/**
     * Returns a copy of the specified temporal object with the specified period added.
     * <p>
     * The period added is a multiple of this unit. For example, this method
     * could be used to add "3 days" to a date by calling this method on the
     * instance representing "days", passing the date and the period "3".
     * The period to be added may be negative, which is equivalent to subtraction.
     * <p>
     * There are two equivalent ways of using this method.
     * The first is to invoke this method directly.
     * The second is to use {@link Temporal#plus(long, TemporalUnit)}:
     * <pre>
     *   // these two lines are equivalent, but the second approach is recommended
     *   temporal = thisUnit.addTo(temporal);
     *   temporal = temporal.plus(thisUnit);
     * </pre>
     * It is recommended to use the second approach, {@code plus(TemporalUnit)},
     * as it is a lot clearer to read in code.
     * <p>
     * Implementations should perform any queries or calculations using the units
     * available in {@link ChronoUnit} or the fields available in {@link ChronoField}.
     * If the unit is not supported an {@code UnsupportedTemporalTypeException} must be thrown.
     * <p>
     * Implementations must not alter the specified temporal object.
     * Instead, an adjusted copy of the original must be returned.
     * This provides equivalent, safe behavior for immutable and mutable implementations.
     *
     * @param <R>  the type of the Temporal object
     * @param temporal  the temporal object to adjust, not null
     * @param amount  the amount of this unit to add, positive or negative
     * @return the adjusted temporal object, not null
     * @throws DateTimeException if the amount cannot be added
     * @throws UnsupportedTemporalTypeException if the unit is not supported by the temporal
     */
    <R extends Temporal> R addTo(R temporal, long amount);

    //-----------------------------------------------------------------------
    
Calculates the amount of time between two temporal objects.

 This calculates the amount in terms of this unit. The start and end points are supplied as temporal objects and must be of compatible types. The implementation will convert the second type to be an instance of the first type before the calculating the amount. The result will be negative if the end is before the start. For example, the amount in hours between two temporal objects can be calculated using HOURS.between(startTime, endTime). 

The calculation returns a whole number, representing the number of
complete units between the two temporals.
For example, the amount in hours between the times 11:30 and 13:29
will only be one hour as it is one minute short of two hours.

 There are two equivalent ways of using this method. The first is to invoke this method directly. The second is to use Temporal.until(Temporal, TemporalUnit): 
  // these two lines are equivalent
  between = thisUnit.between(start, end);
  between = start.until(end, thisUnit);


The choice should be made based on which makes the code more readable.


For example, this method allows the number of days between two dates to
be calculated:

 long daysBetween = DAYS.between(start, end);
 // or alternatively
 long daysBetween = start.until(end, DAYS);



 Implementations should perform any queries or calculations using the units available in ChronoUnit or the fields available in ChronoField. If the unit is not supported an UnsupportedTemporalTypeException must be thrown. Implementations must not alter the specified temporal objects. 
Params:
  • temporal1Inclusive –  the base temporal object, not null
  • temporal2Exclusive –  the other temporal object, exclusive, not null
Throws:
Implementation Requirements: Implementations must begin by checking to if the two temporals have the same type using getClass(). If they do not, then the result must be obtained by calling temporal1Inclusive.until(temporal2Exclusive, this).
Returns:the amount of time between temporal1Inclusive and temporal2Exclusive
 in terms of this unit; positive if temporal2Exclusive is later than
 temporal1Inclusive, negative if earlier
/**
     * Calculates the amount of time between two temporal objects.
     * <p>
     * This calculates the amount in terms of this unit. The start and end
     * points are supplied as temporal objects and must be of compatible types.
     * The implementation will convert the second type to be an instance of the
     * first type before the calculating the amount.
     * The result will be negative if the end is before the start.
     * For example, the amount in hours between two temporal objects can be
     * calculated using {@code HOURS.between(startTime, endTime)}.
     * <p>
     * The calculation returns a whole number, representing the number of
     * complete units between the two temporals.
     * For example, the amount in hours between the times 11:30 and 13:29
     * will only be one hour as it is one minute short of two hours.
     * <p>
     * There are two equivalent ways of using this method.
     * The first is to invoke this method directly.
     * The second is to use {@link Temporal#until(Temporal, TemporalUnit)}:
     * <pre>
     *   // these two lines are equivalent
     *   between = thisUnit.between(start, end);
     *   between = start.until(end, thisUnit);
     * </pre>
     * The choice should be made based on which makes the code more readable.
     * <p>
     * For example, this method allows the number of days between two dates to
     * be calculated:
     * <pre>
     *  long daysBetween = DAYS.between(start, end);
     *  // or alternatively
     *  long daysBetween = start.until(end, DAYS);
     * </pre>
     * <p>
     * Implementations should perform any queries or calculations using the units
     * available in {@link ChronoUnit} or the fields available in {@link ChronoField}.
     * If the unit is not supported an {@code UnsupportedTemporalTypeException} must be thrown.
     * Implementations must not alter the specified temporal objects.
     *
     * @implSpec
     * Implementations must begin by checking to if the two temporals have the
     * same type using {@code getClass()}. If they do not, then the result must be
     * obtained by calling {@code temporal1Inclusive.until(temporal2Exclusive, this)}.
     *
     * @param temporal1Inclusive  the base temporal object, not null
     * @param temporal2Exclusive  the other temporal object, exclusive, not null
     * @return the amount of time between temporal1Inclusive and temporal2Exclusive
     *  in terms of this unit; positive if temporal2Exclusive is later than
     *  temporal1Inclusive, negative if earlier
     * @throws DateTimeException if the amount cannot be calculated, or the end
     *  temporal cannot be converted to the same type as the start temporal
     * @throws UnsupportedTemporalTypeException if the unit is not supported by the temporal
     * @throws ArithmeticException if numeric overflow occurs
     */
    long between(Temporal temporal1Inclusive, Temporal temporal2Exclusive);

    //-----------------------------------------------------------------------
    
Gets a descriptive name for the unit.


This should be in the plural and upper-first camel case, such as 'Days' or 'Minutes'.

Returns:the name of this unit, not null
/**
     * Gets a descriptive name for the unit.
     * <p>
     * This should be in the plural and upper-first camel case, such as 'Days' or 'Minutes'.
     *
     * @return the name of this unit, not null
     */
    @Override
    String toString();

}