1 /*
2 * Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
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 *
39 * * Redistributions of source code must retain the above copyright notice,
40 * this list of conditions and the following disclaimer.
41 *
42 * * Redistributions in binary form must reproduce the above copyright notice,
43 * this list of conditions and the following disclaimer in the documentation
44 * and/or other materials provided with the distribution.
45 *
46 * * Neither the name of JSR-310 nor the names of its contributors
47 * may be used to endorse or promote products derived from this software
48 * without specific prior written permission.
49 *
50 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
51 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
52 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
53 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
54 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
55 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
56 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
57 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
58 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
59 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
60 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
61 */
62 package java.time.temporal;
63
64 import java.time.DateTimeException;
65 import java.time.Duration;
66 import java.time.Period;
67
68 /**
69 * A unit of date-time, such as Days or Hours.
70 * <p>
71 * Measurement of time is built on units, such as years, months, days, hours, minutes and seconds.
72 * Implementations of this interface represent those units.
73 * <p>
74 * An instance of this interface represents the unit itself, rather than an amount of the unit.
75 * See {@link Period} for a class that represents an amount in terms of the common units.
76 * <p>
77 * The most commonly used units are defined in {@link ChronoUnit}.
78 * Further units are supplied in {@link IsoFields}.
79 * Units can also be written by application code by implementing this interface.
80 * <p>
81 * The unit works using double dispatch. Client code calls methods on a date-time like
82 * {@code LocalDateTime} which check if the unit is a {@code ChronoUnit}.
83 * If it is, then the date-time must handle it.
84 * Otherwise, the method call is re-dispatched to the matching method in this interface.
85 *
86 * <h3>Specification for implementors</h3>
87 * This interface must be implemented with care to ensure other classes operate correctly.
88 * All implementations that can be instantiated must be final, immutable and thread-safe.
89 * It is recommended to use an enum where possible.
90 *
91 * @since 1.8
92 */
93 public interface TemporalUnit {
94
95 /**
96 * Gets a descriptive name for the unit.
97 * <p>
98 * This should be in the plural and upper-first camel case, such as 'Days' or 'Minutes'.
99 *
100 * @return the name, not null
101 */
102 String getName();
103
104 /**
105 * Gets the duration of this unit, which may be an estimate.
106 * <p>
107 * All units return a duration measured in standard nanoseconds from this method.
108 * The duration will be positive and non-zero.
109 * For example, an hour has a duration of {@code 60 * 60 * 1,000,000,000ns}.
110 * <p>
111 * Some units may return an accurate duration while others return an estimate.
112 * For example, days have an estimated duration due to the possibility of
113 * daylight saving time changes.
114 * To determine if the duration is an estimate, use {@link #isDurationEstimated()}.
115 *
116 * @return the duration of this unit, which may be an estimate, not null
117 */
118 Duration getDuration();
119
120 /**
121 * Checks if the duration of the unit is an estimate.
122 * <p>
123 * All units have a duration, however the duration is not always accurate.
124 * For example, days have an estimated duration due to the possibility of
125 * daylight saving time changes.
126 * This method returns true if the duration is an estimate and false if it is
127 * accurate. Note that accurate/estimated ignores leap seconds.
128 *
129 * @return true if the duration is estimated, false if accurate
130 */
131 boolean isDurationEstimated();
132
133 //-----------------------------------------------------------------------
134 /**
135 * Checks if this unit is supported by the specified temporal object.
136 * <p>
137 * This checks that the implementing date-time can add/subtract this unit.
138 * This can be used to avoid throwing an exception.
139 * <p>
140 * This default implementation derives the value using
141 * {@link Temporal#plus(long, TemporalUnit)}.
142 *
143 * @param temporal the temporal object to check, not null
144 * @return true if the unit is supported
145 */
146 public default boolean isSupportedBy(Temporal temporal) {
147 try {
148 temporal.plus(1, this);
149 return true;
150 } catch (RuntimeException ex) {
151 try {
152 temporal.plus(-1, this);
153 return true;
154 } catch (RuntimeException ex2) {
155 return false;
156 }
157 }
158 }
159
160 /**
161 * Returns a copy of the specified temporal object with the specified period added.
162 * <p>
163 * The period added is a multiple of this unit. For example, this method
164 * could be used to add "3 days" to a date by calling this method on the
165 * instance representing "days", passing the date and the period "3".
166 * The period to be added may be negative, which is equivalent to subtraction.
167 * <p>
168 * There are two equivalent ways of using this method.
169 * The first is to invoke this method directly.
170 * The second is to use {@link Temporal#plus(long, TemporalUnit)}:
171 * <pre>
172 * // these two lines are equivalent, but the second approach is recommended
173 * temporal = thisUnit.addTo(temporal);
174 * temporal = temporal.plus(thisUnit);
175 * </pre>
176 * It is recommended to use the second approach, {@code plus(TemporalUnit)},
177 * as it is a lot clearer to read in code.
178 * <p>
179 * Implementations should perform any queries or calculations using the units
180 * available in {@link ChronoUnit} or the fields available in {@link ChronoField}.
181 * If the unit is not supported a {@code DateTimeException} must be thrown.
182 * <p>
183 * Implementations must not alter the specified temporal object.
184 * Instead, an adjusted copy of the original must be returned.
185 * This provides equivalent, safe behavior for immutable and mutable implementations.
186 *
187 * @param <R> the type of the Temporal object
188 * @param temporal the temporal object to adjust, not null
189 * @param amount the amount of this unit to add, positive or negative
190 * @return the adjusted temporal object, not null
191 * @throws DateTimeException if the period cannot be added
192 */
193 <R extends Temporal> R addTo(R temporal, long amount);
194
195 //-----------------------------------------------------------------------
196 /**
197 * Calculates the period in terms of this unit between two temporal objects
198 * of the same type.
199 * <p>
200 * This calculates the period between two temporals in terms of this unit.
201 * The start and end points are supplied as temporal objects and must be
202 * of the same type.
203 * The result will be negative if the end is before the start.
204 * For example, the period in hours between two temporal objects can be
205 * calculated using {@code HOURS.between(startTime, endTime)}.
206 * <p>
207 * The calculation returns a whole number, representing the number of
208 * complete units between the two temporals.
209 * For example, the period in hours between the times 11:30 and 13:29
210 * will only be one hour as it is one minute short of two hours.
211 * <p>
212 * There are two equivalent ways of using this method.
213 * The first is to invoke this method directly.
214 * The second is to use {@link Temporal#periodUntil(Temporal, TemporalUnit)}:
215 * <pre>
216 * // these two lines are equivalent
217 * temporal = thisUnit.between(start, end);
218 * temporal = start.periodUntil(end, thisUnit);
219 * </pre>
220 * The choice should be made based on which makes the code more readable.
221 * <p>
222 * For example, this method allows the number of days between two dates to
223 * be calculated:
224 * <pre>
225 * long daysBetween = DAYS.between(start, end);
226 * // or alternatively
227 * long daysBetween = start.periodUntil(end, DAYS);
228 * </pre>
229 * <p>
230 * Implementations should perform any queries or calculations using the units
231 * available in {@link ChronoUnit} or the fields available in {@link ChronoField}.
232 * If the unit is not supported a {@code DateTimeException} must be thrown.
233 * Implementations must not alter the specified temporal objects.
234 *
235 * @param temporal1 the base temporal object, not null
236 * @param temporal2 the other temporal object, not null
237 * @return the period between datetime1 and datetime2 in terms of this unit;
238 * positive if datetime2 is later than datetime1, negative if earlier
239 * @throws DateTimeException if the period cannot be calculated
240 * @throws ArithmeticException if numeric overflow occurs
241 */
242 long between(Temporal temporal1, Temporal temporal2);
243
244 //-----------------------------------------------------------------------
245 /**
246 * Outputs this unit as a {@code String} using the name.
247 *
248 * @return the name of this unit, not null
249 */
250 @Override
251 String toString();
252
253 }