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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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25
26/*
27 * This file is available under and governed by the GNU General Public
28 * License version 2 only, as published by the Free Software Foundation.
29 * However, the following notice accompanied the original version of this
30 * file:
31 *
32 * Copyright (c) 2012, 2013 Stephen Colebourne & Michael Nascimento Santos
33 *
34 * All rights reserved.
35 *
36 * Redistribution and use in source and binary forms, with or without
37 * modification, are permitted provided that the following conditions are met:
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48 *    without specific prior written permission.
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61 */
62package java.time.temporal;
63
64import java.time.DateTimeException;
65import java.time.Duration;
66import java.time.Period;
67import java.util.List;
68
69/**
70 * Framework-level interface defining an amount of time, such as
71 * "6 hours", "8 days" or "2 years and 3 months".
72 * <p>
73 * This is the base interface type for amounts of time.
74 * An amount is distinct from a date or time-of-day in that it is not tied
75 * to any specific point on the time-line.
76 * <p>
77 * The amount can be thought of as a {@code Map} of {@link TemporalUnit} to
78 * {@code long}, exposed via {@link #getUnits()} and {@link #get(TemporalUnit)}.
79 * A simple case might have a single unit-value pair, such as "6 hours".
80 * A more complex case may have multiple unit-value pairs, such as
81 * "7 years, 3 months and 5 days".
82 * <p>
83 * There are two common implementations.
84 * {@link Period} is a date-based implementation, storing years, months and days.
85 * {@link Duration} is a time-based implementation, storing seconds and nanoseconds,
86 * but providing some access using other duration based units such as minutes,
87 * hours and fixed 24-hour days.
88 * <p>
89 * This interface is a framework-level interface that should not be widely
90 * used in application code. Instead, applications should create and pass
91 * around instances of concrete types, such as {@code Period} and {@code Duration}.
92 *
93 * @implSpec
94 * This interface places no restrictions on the mutability of implementations,
95 * however immutability is strongly recommended.
96 *
97 * @since 1.8
98 */
99public interface TemporalAmount {
100
101    /**
102     * Returns the value of the requested unit.
103     * The units returned from {@link #getUnits()} uniquely define the
104     * value of the {@code TemporalAmount}.  A value must be returned
105     * for each unit listed in {@code getUnits}.
106     *
107     * @implSpec
108     * Implementations may declare support for units not listed by {@link #getUnits()}.
109     * Typically, the implementation would define additional units
110     * as conversions for the convenience of developers.
111     *
112     * @param unit the {@code TemporalUnit} for which to return the value
113     * @return the long value of the unit
114     * @throws DateTimeException if a value for the unit cannot be obtained
115     * @throws UnsupportedTemporalTypeException if the {@code unit} is not supported
116     */
117    long get(TemporalUnit unit);
118
119    /**
120     * Returns the list of units uniquely defining the value of this TemporalAmount.
121     * The list of {@code TemporalUnits} is defined by the implementation class.
122     * The list is a snapshot of the units at the time {@code getUnits}
123     * is called and is not mutable.
124     * The units are ordered from longest duration to the shortest duration
125     * of the unit.
126     *
127     * @implSpec
128     * The list of units completely and uniquely represents the
129     * state of the object without omissions, overlaps or duplication.
130     * The units are in order from longest duration to shortest.
131     *
132     * @return the List of {@code TemporalUnits}; not null
133     */
134    List<TemporalUnit> getUnits();
135
136    /**
137     * Adds to the specified temporal object.
138     * <p>
139     * Adds the amount to the specified temporal object using the logic
140     * encapsulated in the implementing class.
141     * <p>
142     * There are two equivalent ways of using this method.
143     * The first is to invoke this method directly.
144     * The second is to use {@link Temporal#plus(TemporalAmount)}:
145     * <pre>
146     *   // These two lines are equivalent, but the second approach is recommended
147     *   dateTime = amount.addTo(dateTime);
148     *   dateTime = dateTime.plus(adder);
149     * </pre>
150     * It is recommended to use the second approach, {@code plus(TemporalAmount)},
151     * as it is a lot clearer to read in code.
152     *
153     * @implSpec
154     * The implementation must take the input object and add to it.
155     * The implementation defines the logic of the addition and is responsible for
156     * documenting that logic. It may use any method on {@code Temporal} to
157     * query the temporal object and perform the addition.
158     * The returned object must have the same observable type as the input object
159     * <p>
160     * The input object must not be altered.
161     * Instead, an adjusted copy of the original must be returned.
162     * This provides equivalent, safe behavior for immutable and mutable temporal objects.
163     * <p>
164     * The input temporal object may be in a calendar system other than ISO.
165     * Implementations may choose to document compatibility with other calendar systems,
166     * or reject non-ISO temporal objects by {@link TemporalQueries#chronology() querying the chronology}.
167     * <p>
168     * This method may be called from multiple threads in parallel.
169     * It must be thread-safe when invoked.
170     *
171     * @param temporal  the temporal object to add the amount to, not null
172     * @return an object of the same observable type with the addition made, not null
173     * @throws DateTimeException if unable to add
174     * @throws ArithmeticException if numeric overflow occurs
175     */
176    Temporal addTo(Temporal temporal);
177
178    /**
179     * Subtracts this object from the specified temporal object.
180     * <p>
181     * Subtracts the amount from the specified temporal object using the logic
182     * encapsulated in the implementing class.
183     * <p>
184     * There are two equivalent ways of using this method.
185     * The first is to invoke this method directly.
186     * The second is to use {@link Temporal#minus(TemporalAmount)}:
187     * <pre>
188     *   // these two lines are equivalent, but the second approach is recommended
189     *   dateTime = amount.subtractFrom(dateTime);
190     *   dateTime = dateTime.minus(amount);
191     * </pre>
192     * It is recommended to use the second approach, {@code minus(TemporalAmount)},
193     * as it is a lot clearer to read in code.
194     *
195     * @implSpec
196     * The implementation must take the input object and subtract from it.
197     * The implementation defines the logic of the subtraction and is responsible for
198     * documenting that logic. It may use any method on {@code Temporal} to
199     * query the temporal object and perform the subtraction.
200     * The returned object must have the same observable type as the input object
201     * <p>
202     * The input object must not be altered.
203     * Instead, an adjusted copy of the original must be returned.
204     * This provides equivalent, safe behavior for immutable and mutable temporal objects.
205     * <p>
206     * The input temporal object may be in a calendar system other than ISO.
207     * Implementations may choose to document compatibility with other calendar systems,
208     * or reject non-ISO temporal objects by {@link TemporalQueries#chronology() querying the chronology}.
209     * <p>
210     * This method may be called from multiple threads in parallel.
211     * It must be thread-safe when invoked.
212     *
213     * @param temporal  the temporal object to subtract the amount from, not null
214     * @return an object of the same observable type with the subtraction made, not null
215     * @throws DateTimeException if unable to subtract
216     * @throws ArithmeticException if numeric overflow occurs
217     */
218    Temporal subtractFrom(Temporal temporal);
219}
220