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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, 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:
38   *
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40   *    this list of conditions and the following disclaimer.
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43   *    this list of conditions and the following disclaimer in the documentation
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62  package java.time.temporal;
63  
64  import java.time.DateTimeException;
65  import java.time.Duration;
66  import java.time.LocalTime;
67  import java.time.Period;
68  import java.time.chrono.ChronoLocalDate;
69  import java.time.chrono.ChronoLocalDateTime;
70  import java.time.chrono.ChronoZonedDateTime;
71  
72  /**
73   * A unit of date-time, such as Days or Hours.
74   * <p>
75   * Measurement of time is built on units, such as years, months, days, hours, minutes and seconds.
76   * Implementations of this interface represent those units.
77   * <p>
78   * An instance of this interface represents the unit itself, rather than an amount of the unit.
79   * See {@link Period} for a class that represents an amount in terms of the common units.
80   * <p>
81   * The most commonly used units are defined in {@link ChronoUnit}.
82   * Further units are supplied in {@link IsoFields}.
83   * Units can also be written by application code by implementing this interface.
84   * <p>
85   * The unit works using double dispatch. Client code calls methods on a date-time like
86   * {@code LocalDateTime} which check if the unit is a {@code ChronoUnit}.
87   * If it is, then the date-time must handle it.
88   * Otherwise, the method call is re-dispatched to the matching method in this interface.
89   *
90   * @implSpec
91   * This interface must be implemented with care to ensure other classes operate correctly.
92   * All implementations that can be instantiated must be final, immutable and thread-safe.
93   * It is recommended to use an enum where possible.
94   *
95   * @since 1.8
96   */
97  public interface TemporalUnit {
98  
99      /**
100      * Gets the duration of this unit, which may be an estimate.
101      * <p>
102      * All units return a duration measured in standard nanoseconds from this method.
103      * The duration will be positive and non-zero.
104      * For example, an hour has a duration of {@code 60 * 60 * 1,000,000,000ns}.
105      * <p>
106      * Some units may return an accurate duration while others return an estimate.
107      * For example, days have an estimated duration due to the possibility of
108      * daylight saving time changes.
109      * To determine if the duration is an estimate, use {@link #isDurationEstimated()}.
110      *
111      * @return the duration of this unit, which may be an estimate, not null
112      */
113     Duration getDuration();
114 
115     /**
116      * Checks if the duration of the unit is an estimate.
117      * <p>
118      * All units have a duration, however the duration is not always accurate.
119      * For example, days have an estimated duration due to the possibility of
120      * daylight saving time changes.
121      * This method returns true if the duration is an estimate and false if it is
122      * accurate. Note that accurate/estimated ignores leap seconds.
123      *
124      * @return true if the duration is estimated, false if accurate
125      */
126     boolean isDurationEstimated();
127 
128     //-----------------------------------------------------------------------
129     /**
130      * Checks if this unit represents a component of a date.
131      * <p>
132      * A date is time-based if it can be used to imply meaning from a date.
133      * It must have a {@linkplain #getDuration() duration} that is an integral
134      * multiple of the length of a standard day.
135      * Note that it is valid for both {@code isDateBased()} and {@code isTimeBased()}
136      * to return false, such as when representing a unit like 36 hours.
137      *
138      * @return true if this unit is a component of a date
139      */
140     boolean isDateBased();
141 
142     /**
143      * Checks if this unit represents a component of a time.
144      * <p>
145      * A unit is time-based if it can be used to imply meaning from a time.
146      * It must have a {@linkplain #getDuration() duration} that divides into
147      * the length of a standard day without remainder.
148      * Note that it is valid for both {@code isDateBased()} and {@code isTimeBased()}
149      * to return false, such as when representing a unit like 36 hours.
150      *
151      * @return true if this unit is a component of a time
152      */
153     boolean isTimeBased();
154 
155     //-----------------------------------------------------------------------
156     /**
157      * Checks if this unit is supported by the specified temporal object.
158      * <p>
159      * This checks that the implementing date-time can add/subtract this unit.
160      * This can be used to avoid throwing an exception.
161      * <p>
162      * This default implementation derives the value using
163      * {@link Temporal#plus(long, TemporalUnit)}.
164      *
165      * @param temporal  the temporal object to check, not null
166      * @return true if the unit is supported
167      */
168     default boolean isSupportedBy(Temporal temporal) {
169         if (temporal instanceof LocalTime) {
170             return isTimeBased();
171         }
172         if (temporal instanceof ChronoLocalDate) {
173             return isDateBased();
174         }
175         if (temporal instanceof ChronoLocalDateTime || temporal instanceof ChronoZonedDateTime) {
176             return true;
177         }
178         try {
179             temporal.plus(1, this);
180             return true;
181         } catch (UnsupportedTemporalTypeException ex) {
182             return false;
183         } catch (RuntimeException ex) {
184             try {
185                 temporal.plus(-1, this);
186                 return true;
187             } catch (RuntimeException ex2) {
188                 return false;
189             }
190         }
191     }
192 
193     /**
194      * Returns a copy of the specified temporal object with the specified period added.
195      * <p>
196      * The period added is a multiple of this unit. For example, this method
197      * could be used to add "3 days" to a date by calling this method on the
198      * instance representing "days", passing the date and the period "3".
199      * The period to be added may be negative, which is equivalent to subtraction.
200      * <p>
201      * There are two equivalent ways of using this method.
202      * The first is to invoke this method directly.
203      * The second is to use {@link Temporal#plus(long, TemporalUnit)}:
204      * <pre>
205      *   // these two lines are equivalent, but the second approach is recommended
206      *   temporal = thisUnit.addTo(temporal);
207      *   temporal = temporal.plus(thisUnit);
208      * </pre>
209      * It is recommended to use the second approach, {@code plus(TemporalUnit)},
210      * as it is a lot clearer to read in code.
211      * <p>
212      * Implementations should perform any queries or calculations using the units
213      * available in {@link ChronoUnit} or the fields available in {@link ChronoField}.
214      * If the unit is not supported an {@code UnsupportedTemporalTypeException} must be thrown.
215      * <p>
216      * Implementations must not alter the specified temporal object.
217      * Instead, an adjusted copy of the original must be returned.
218      * This provides equivalent, safe behavior for immutable and mutable implementations.
219      *
220      * @param <R>  the type of the Temporal object
221      * @param temporal  the temporal object to adjust, not null
222      * @param amount  the amount of this unit to add, positive or negative
223      * @return the adjusted temporal object, not null
224      * @throws DateTimeException if the period cannot be added
225      * @throws UnsupportedTemporalTypeException if the unit is not supported by the temporal
226      */
227     <R extends Temporal> R addTo(R temporal, long amount);
228 
229     //-----------------------------------------------------------------------
230     /**
231      * Calculates the amount of time between two temporal objects.
232      * <p>
233      * This calculates the amount in terms of this unit. The start and end
234      * points are supplied as temporal objects and must be of compatible types.
235      * The implementation will convert the second type to be an instance of the
236      * first type before the calculating the amount.
237      * The result will be negative if the end is before the start.
238      * For example, the amount in hours between two temporal objects can be
239      * calculated using {@code HOURS.between(startTime, endTime)}.
240      * <p>
241      * The calculation returns a whole number, representing the number of
242      * complete units between the two temporals.
243      * For example, the amount in hours between the times 11:30 and 13:29
244      * will only be one hour as it is one minute short of two hours.
245      * <p>
246      * There are two equivalent ways of using this method.
247      * The first is to invoke this method directly.
248      * The second is to use {@link Temporal#until(Temporal, TemporalUnit)}:
249      * <pre>
250      *   // these two lines are equivalent
251      *   between = thisUnit.between(start, end);
252      *   between = start.until(end, thisUnit);
253      * </pre>
254      * The choice should be made based on which makes the code more readable.
255      * <p>
256      * For example, this method allows the number of days between two dates to
257      * be calculated:
258      * <pre>
259      *  long daysBetween = DAYS.between(start, end);
260      *  // or alternatively
261      *  long daysBetween = start.until(end, DAYS);
262      * </pre>
263      * <p>
264      * Implementations should perform any queries or calculations using the units
265      * available in {@link ChronoUnit} or the fields available in {@link ChronoField}.
266      * If the unit is not supported an {@code UnsupportedTemporalTypeException} must be thrown.
267      * Implementations must not alter the specified temporal objects.
268      *
269      * @implSpec
270      * Implementations must begin by checking to if the two temporals have the
271      * same type using {@code getClass()}. If they do not, then the result must be
272      * obtained by calling {@code temporal1Inclusive.until(temporal2Exclusive, this)}.
273      *
274      * @param temporal1Inclusive  the base temporal object, not null
275      * @param temporal2Exclusive  the other temporal object, exclusive, not null
276      * @return the amount of time between temporal1Inclusive and temporal2Exclusive
277      *  in terms of this unit; positive if temporal2Exclusive is later than
278      *  temporal1Inclusive, negative if earlier
279      * @throws DateTimeException if the amount cannot be calculated, or the end
280      *  temporal cannot be converted to the same type as the start temporal
281      * @throws UnsupportedTemporalTypeException if the unit is not supported by the temporal
282      * @throws ArithmeticException if numeric overflow occurs
283      */
284     long between(Temporal temporal1Inclusive, Temporal temporal2Exclusive);
285 
286     //-----------------------------------------------------------------------
287     /**
288      * Gets a descriptive name for the unit.
289      * <p>
290      * This should be in the plural and upper-first camel case, such as 'Days' or 'Minutes'.
291      *
292      * @return the name of this unit, not null
293      */
294     @Override
295     String toString();
296 
297 }