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	/*
	* 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
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	/*
	* 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, 2013 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,
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	* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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	* 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.Period;
	import java.util.List;

	/**
	* Framework-level interface defining an amount of time, such as
	* "6 hours", "8 days" or "2 years and 3 months".
	* <p>
	* This is the base interface type for amounts of time.
	* An amount is distinct from a date or time-of-day in that it is not tied
	* to any specific point on the time-line.
	* <p>
	* The amount can be thought of as a {@code Map} of {@link TemporalUnit} to
	* {@code long}, exposed via {@link #getUnits()} and {@link #get(TemporalUnit)}.
	* A simple case might have a single unit-value pair, such as "6 hours".
	* A more complex case may have multiple unit-value pairs, such as
	* "7 years, 3 months and 5 days".
	* <p>
	* There are two common implementations.
	* {@link Period} is a date-based implementation, storing years, months and days.
	* {@link Duration} is a time-based implementation, storing seconds and nanoseconds,
	* but providing some access using other duration based units such as minutes,
	* hours and fixed 24-hour days.
	* <p>
	* This interface is a framework-level interface that should not be widely
	* used in application code. Instead, applications should create and pass
	* around instances of concrete types, such as {@code Period} and {@code Duration}.
	*
	* @implSpec
	* This interface places no restrictions on the mutability of implementations,
	* however immutability is strongly recommended.
	*
	* @since 1.8
	*/
	public interface TemporalAmount {

	/**
	* Returns the value of the requested unit.
	* The units returned from {@link #getUnits()} uniquely define the
	* value of the {@code TemporalAmount}. A value must be returned
	* for each unit listed in {@code getUnits}.
	*
	* @implSpec
	* Implementations may declare support for units not listed by {@link #getUnits()}.
	* Typically, the implementation would define additional units
	* as conversions for the convenience of developers.
	*
	* @param unit the {@code TemporalUnit} for which to return the value
	* @return the long value of the unit
	* @throws DateTimeException if a value for the unit cannot be obtained
	* @throws UnsupportedTemporalTypeException if the {@code unit} is not supported
	*/
	long get(TemporalUnit unit);

	/**
	* Returns the list of units uniquely defining the value of this TemporalAmount.
	* The list of {@code TemporalUnits} is defined by the implementation class.
	* The list is a snapshot of the units at the time {@code getUnits}
	* is called and is not mutable.
	* The units are ordered from longest duration to the shortest duration
	* of the unit.
	*
	* @implSpec
	* The list of units completely and uniquely represents the
	* state of the object without omissions, overlaps or duplication.
	* The units are in order from longest duration to shortest.
	*
	* @return the List of {@code TemporalUnits}; not null
	*/
	List<TemporalUnit> getUnits();

	/**
	* Adds to the specified temporal object.
	* <p>
	* Adds the amount to the specified temporal object using the logic
	* encapsulated in the implementing class.
	* <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(TemporalAmount)}:
	* <pre>
	* // These two lines are equivalent, but the second approach is recommended
	* dateTime = amount.addTo(dateTime);
	* dateTime = dateTime.plus(adder);
	* </pre>
	* It is recommended to use the second approach, {@code plus(TemporalAmount)},
	* as it is a lot clearer to read in code.
	*
	* @implSpec
	* The implementation must take the input object and add to it.
	* The implementation defines the logic of the addition and is responsible for
	* documenting that logic. It may use any method on {@code Temporal} to
	* query the temporal object and perform the addition.
	* The returned object must have the same observable type as the input object
	* <p>
	* The input object must not be altered.
	* Instead, an adjusted copy of the original must be returned.
	* This provides equivalent, safe behavior for immutable and mutable temporal objects.
	* <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 add the amount to, not null
	* @return an object of the same observable type with the addition made, not null
	* @throws DateTimeException if unable to add
	* @throws ArithmeticException if numeric overflow occurs
	*/
	Temporal addTo(Temporal temporal);

	/**
	* Subtracts this object from the specified temporal object.
	* <p>
	* Subtracts the amount from the specified temporal object using the logic
	* encapsulated in the implementing class.
	* <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#minus(TemporalAmount)}:
	* <pre>
	* // these two lines are equivalent, but the second approach is recommended
	* dateTime = amount.subtractFrom(dateTime);
	* dateTime = dateTime.minus(amount);
	* </pre>
	* It is recommended to use the second approach, {@code minus(TemporalAmount)},
	* as it is a lot clearer to read in code.
	*
	* @implSpec
	* The implementation must take the input object and subtract from it.
	* The implementation defines the logic of the subtraction and is responsible for
	* documenting that logic. It may use any method on {@code Temporal} to
	* query the temporal object and perform the subtraction.
	* The returned object must have the same observable type as the input object
	* <p>
	* The input object must not be altered.
	* Instead, an adjusted copy of the original must be returned.
	* This provides equivalent, safe behavior for immutable and mutable temporal objects.
	* <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 subtract the amount from, not null
	* @return an object of the same observable type with the subtraction made, not null
	* @throws DateTimeException if unable to subtract
	* @throws ArithmeticException if numeric overflow occurs
	*/
	Temporal subtractFrom(Temporal temporal);
	}

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