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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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10 *
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13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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15 * accompanied this code).
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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) 2007-2012, 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
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61 */
62 package java.time.temporal;
63
64 import static java.time.temporal.ChronoField.EPOCH_DAY;
65 import static java.time.temporal.ChronoField.NANO_OF_DAY;
66 import static java.time.temporal.ChronoField.OFFSET_SECONDS;
67
68 import java.time.LocalDate;
69 import java.time.LocalTime;
70 import java.time.ZoneId;
71 import java.time.ZoneOffset;
72 import java.time.chrono.Chronology;
73
74 /**
75 * Common implementations of {@code TemporalQuery}.
76 * <p>
77 * This class provides common implementations of {@link TemporalQuery}.
78 * These are defined here as they must be constants, and the definition
79 * of lambdas does not guarantee that. By assigning them once here,
80 * they become 'normal' Java constants.
81 * <p>
82 * Queries are a key tool for extracting information from temporal objects.
83 * They exist to externalize the process of querying, permitting different
84 * approaches, as per the strategy design pattern.
85 * Examples might be a query that checks if the date is the day before February 29th
86 * in a leap year, or calculates the number of days to your next birthday.
87 * <p>
88 * The {@link TemporalField} interface provides another mechanism for querying
89 * temporal objects. That interface is limited to returning a {@code long}.
90 * By contrast, queries can return any type.
91 * <p>
92 * There are two equivalent ways of using a {@code TemporalQuery}.
93 * The first is to invoke the method on this interface directly.
94 * The second is to use {@link TemporalAccessor#query(TemporalQuery)}:
95 * <pre>
96 * // these two lines are equivalent, but the second approach is recommended
97 * temporal = thisQuery.queryFrom(temporal);
98 * temporal = temporal.query(thisQuery);
99 * </pre>
100 * It is recommended to use the second approach, {@code query(TemporalQuery)},
101 * as it is a lot clearer to read in code.
102 * <p>
103 * The most common implementations are method references, such as
104 * {@code LocalDate::from} and {@code ZoneId::from}.
105 * Additional common queries are provided to return:
106 * <ul>
107 * <li> a Chronology,
108 * <li> a LocalDate,
109 * <li> a LocalTime,
110 * <li> a ZoneOffset,
111 * <li> a precision,
112 * <li> a zone, or
113 * <li> a zoneId.
114 * </ul>
115 *
116 * @since 1.8
117 */
118 public final class TemporalQueries {
119 // note that it is vital that each method supplies a constant, not a
120 // calculated value, as they will be checked for using ==
121 // it is also vital that each constant is different (due to the == checking)
122 // as such, alterations to this code must be done with care
123
124 /**
125 * Private constructor since this is a utility class.
126 */
127 private TemporalQueries() {
128 }
129
130 //-----------------------------------------------------------------------
131 // special constants should be used to extract information from a TemporalAccessor
132 // that cannot be derived in other ways
133 // Javadoc added here, so as to pretend they are more normal than they really are
134
135 /**
136 * A strict query for the {@code ZoneId}.
137 * <p>
138 * This queries a {@code TemporalAccessor} for the zone.
139 * The zone is only returned if the date-time conceptually contains a {@code ZoneId}.
140 * It will not be returned if the date-time only conceptually has an {@code ZoneOffset}.
141 * Thus a {@link java.time.ZonedDateTime} will return the result of {@code getZone()},
142 * but an {@link java.time.OffsetDateTime} will return null.
143 * <p>
144 * In most cases, applications should use {@link #zone()} as this query is too strict.
145 * <p>
146 * The result from JDK classes implementing {@code TemporalAccessor} is as follows:<br>
147 * {@code LocalDate} returns null<br>
148 * {@code LocalTime} returns null<br>
149 * {@code LocalDateTime} returns null<br>
150 * {@code ZonedDateTime} returns the associated zone<br>
151 * {@code OffsetTime} returns null<br>
152 * {@code OffsetDateTime} returns null<br>
153 * {@code ChronoLocalDate} returns null<br>
154 * {@code ChronoLocalDateTime} returns null<br>
155 * {@code ChronoZonedDateTime} returns the associated zone<br>
156 * {@code Era} returns null<br>
157 * {@code DayOfWeek} returns null<br>
158 * {@code Month} returns null<br>
159 * {@code Year} returns null<br>
160 * {@code YearMonth} returns null<br>
161 * {@code MonthDay} returns null<br>
162 * {@code ZoneOffset} returns null<br>
163 * {@code Instant} returns null<br>
164 *
165 * @return a query that can obtain the zone ID of a temporal, not null
166 */
167 public static TemporalQuery<ZoneId> zoneId() {
168 return TemporalQueries.ZONE_ID;
169 }
170
171 /**
172 * A query for the {@code Chronology}.
173 * <p>
174 * This queries a {@code TemporalAccessor} for the chronology.
175 * If the target {@code TemporalAccessor} represents a date, or part of a date,
176 * then it should return the chronology that the date is expressed in.
177 * As a result of this definition, objects only representing time, such as
178 * {@code LocalTime}, will return null.
179 * <p>
180 * The result from JDK classes implementing {@code TemporalAccessor} is as follows:<br>
181 * {@code LocalDate} returns {@code IsoChronology.INSTANCE}<br>
182 * {@code LocalTime} returns null (does not represent a date)<br>
183 * {@code LocalDateTime} returns {@code IsoChronology.INSTANCE}<br>
184 * {@code ZonedDateTime} returns {@code IsoChronology.INSTANCE}<br>
185 * {@code OffsetTime} returns null (does not represent a date)<br>
186 * {@code OffsetDateTime} returns {@code IsoChronology.INSTANCE}<br>
187 * {@code ChronoLocalDate} returns the associated chronology<br>
188 * {@code ChronoLocalDateTime} returns the associated chronology<br>
189 * {@code ChronoZonedDateTime} returns the associated chronology<br>
190 * {@code Era} returns the associated chronology<br>
191 * {@code DayOfWeek} returns null (shared across chronologies)<br>
192 * {@code Month} returns {@code IsoChronology.INSTANCE}<br>
193 * {@code Year} returns {@code IsoChronology.INSTANCE}<br>
194 * {@code YearMonth} returns {@code IsoChronology.INSTANCE}<br>
195 * {@code MonthDay} returns null {@code IsoChronology.INSTANCE}<br>
196 * {@code ZoneOffset} returns null (does not represent a date)<br>
197 * {@code Instant} returns null (does not represent a date)<br>
198 * <p>
199 * The method {@link java.time.chrono.Chronology#from(TemporalAccessor)} can be used as a
200 * {@code TemporalQuery} via a method reference, {@code Chronology::from}.
201 * That method is equivalent to this query, except that it throws an
202 * exception if a chronology cannot be obtained.
203 *
204 * @return a query that can obtain the chronology of a temporal, not null
205 */
206 public static TemporalQuery<Chronology> chronology() {
207 return TemporalQueries.CHRONO;
208 }
209
210 /**
211 * A query for the smallest supported unit.
212 * <p>
213 * This queries a {@code TemporalAccessor} for the time precision.
214 * If the target {@code TemporalAccessor} represents a consistent or complete date-time,
215 * date or time then this must return the smallest precision actually supported.
216 * Note that fields such as {@code NANO_OF_DAY} and {@code NANO_OF_SECOND}
217 * are defined to always return ignoring the precision, thus this is the only
218 * way to find the actual smallest supported unit.
219 * For example, were {@code GregorianCalendar} to implement {@code TemporalAccessor}
220 * it would return a precision of {@code MILLIS}.
221 * <p>
222 * The result from JDK classes implementing {@code TemporalAccessor} is as follows:<br>
223 * {@code LocalDate} returns {@code DAYS}<br>
224 * {@code LocalTime} returns {@code NANOS}<br>
225 * {@code LocalDateTime} returns {@code NANOS}<br>
226 * {@code ZonedDateTime} returns {@code NANOS}<br>
227 * {@code OffsetTime} returns {@code NANOS}<br>
228 * {@code OffsetDateTime} returns {@code NANOS}<br>
229 * {@code ChronoLocalDate} returns {@code DAYS}<br>
230 * {@code ChronoLocalDateTime} returns {@code NANOS}<br>
231 * {@code ChronoZonedDateTime} returns {@code NANOS}<br>
232 * {@code Era} returns {@code ERAS}<br>
233 * {@code DayOfWeek} returns {@code DAYS}<br>
234 * {@code Month} returns {@code MONTHS}<br>
235 * {@code Year} returns {@code YEARS}<br>
236 * {@code YearMonth} returns {@code MONTHS}<br>
237 * {@code MonthDay} returns null (does not represent a complete date or time)<br>
238 * {@code ZoneOffset} returns null (does not represent a date or time)<br>
239 * {@code Instant} returns {@code NANOS}<br>
240 *
241 * @return a query that can obtain the precision of a temporal, not null
242 */
243 public static TemporalQuery<TemporalUnit> precision() {
244 return TemporalQueries.PRECISION;
245 }
246
247 //-----------------------------------------------------------------------
248 // non-special constants are standard queries that derive information from other information
249 /**
250 * A lenient query for the {@code ZoneId}, falling back to the {@code ZoneOffset}.
251 * <p>
252 * This queries a {@code TemporalAccessor} for the zone.
253 * It first tries to obtain the zone, using {@link #zoneId()}.
254 * If that is not found it tries to obtain the {@link #offset()}.
255 * Thus a {@link java.time.ZonedDateTime} will return the result of {@code getZone()},
256 * while an {@link java.time.OffsetDateTime} will return the result of {@code getOffset()}.
257 * <p>
258 * In most cases, applications should use this query rather than {@code #zoneId()}.
259 * <p>
260 * The method {@link ZoneId#from(TemporalAccessor)} can be used as a
261 * {@code TemporalQuery} via a method reference, {@code ZoneId::from}.
262 * That method is equivalent to this query, except that it throws an
263 * exception if a zone cannot be obtained.
264 *
265 * @return a query that can obtain the zone ID or offset of a temporal, not null
266 */
267 public static TemporalQuery<ZoneId> zone() {
268 return TemporalQueries.ZONE;
269 }
270
271 /**
272 * A query for {@code ZoneOffset} returning null if not found.
273 * <p>
274 * This returns a {@code TemporalQuery} that can be used to query a temporal
275 * object for the offset. The query will return null if the temporal
276 * object cannot supply an offset.
277 * <p>
278 * The query implementation examines the {@link ChronoField#OFFSET_SECONDS OFFSET_SECONDS}
279 * field and uses it to create a {@code ZoneOffset}.
280 * <p>
281 * The method {@link java.time.ZoneOffset#from(TemporalAccessor)} can be used as a
282 * {@code TemporalQuery} via a method reference, {@code ZoneOffset::from}.
283 * This query and {@code ZoneOffset::from} will return the same result if the
284 * temporal object contains an offset. If the temporal object does not contain
285 * an offset, then the method reference will throw an exception, whereas this
286 * query will return null.
287 *
288 * @return a query that can obtain the offset of a temporal, not null
289 */
290 public static TemporalQuery<ZoneOffset> offset() {
291 return TemporalQueries.OFFSET;
292 }
293
294 /**
295 * A query for {@code LocalDate} returning null if not found.
296 * <p>
297 * This returns a {@code TemporalQuery} that can be used to query a temporal
298 * object for the local date. The query will return null if the temporal
299 * object cannot supply a local date.
300 * <p>
301 * The query implementation examines the {@link ChronoField#EPOCH_DAY EPOCH_DAY}
302 * field and uses it to create a {@code LocalDate}.
303 * <p>
304 * The method {@link ZoneOffset#from(TemporalAccessor)} can be used as a
305 * {@code TemporalQuery} via a method reference, {@code LocalDate::from}.
306 * This query and {@code LocalDate::from} will return the same result if the
307 * temporal object contains a date. If the temporal object does not contain
308 * a date, then the method reference will throw an exception, whereas this
309 * query will return null.
310 *
311 * @return a query that can obtain the date of a temporal, not null
312 */
313 public static TemporalQuery<LocalDate> localDate() {
314 return TemporalQueries.LOCAL_DATE;
315 }
316
317 /**
318 * A query for {@code LocalTime} returning null if not found.
319 * <p>
320 * This returns a {@code TemporalQuery} that can be used to query a temporal
321 * object for the local time. The query will return null if the temporal
322 * object cannot supply a local time.
323 * <p>
324 * The query implementation examines the {@link ChronoField#NANO_OF_DAY NANO_OF_DAY}
325 * field and uses it to create a {@code LocalTime}.
326 * <p>
327 * The method {@link ZoneOffset#from(TemporalAccessor)} can be used as a
328 * {@code TemporalQuery} via a method reference, {@code LocalTime::from}.
329 * This query and {@code LocalTime::from} will return the same result if the
330 * temporal object contains a time. If the temporal object does not contain
331 * a time, then the method reference will throw an exception, whereas this
332 * query will return null.
333 *
334 * @return a query that can obtain the time of a temporal, not null
335 */
336 public static TemporalQuery<LocalTime> localTime() {
337 return TemporalQueries.LOCAL_TIME;
338 }
339
340 //-----------------------------------------------------------------------
341 /**
342 * A strict query for the {@code ZoneId}.
343 */
344 static final TemporalQuery<ZoneId> ZONE_ID = new TemporalQuery<>() {
345 @Override
346 public ZoneId queryFrom(TemporalAccessor temporal) {
347 return temporal.query(TemporalQueries.ZONE_ID);
348 }
349
350 @Override
351 public String toString() {
352 return "ZoneId";
353 }
354 };
355
356 /**
357 * A query for the {@code Chronology}.
358 */
359 static final TemporalQuery<Chronology> CHRONO = new TemporalQuery<>() {
360 @Override
361 public Chronology queryFrom(TemporalAccessor temporal) {
362 return temporal.query(TemporalQueries.CHRONO);
363 }
364
365 @Override
366 public String toString() {
367 return "Chronology";
368 }
369 };
370
371
372 /**
373 * A query for the smallest supported unit.
374 */
375 static final TemporalQuery<TemporalUnit> PRECISION = new TemporalQuery<>() {
376 @Override
377 public TemporalUnit queryFrom(TemporalAccessor temporal) {
378 return temporal.query(TemporalQueries.PRECISION);
379 }
380
381 @Override
382 public String toString() {
383 return "Precision";
384 }
385 };
386
387 //-----------------------------------------------------------------------
388 /**
389 * A query for {@code ZoneOffset} returning null if not found.
390 */
391 static final TemporalQuery<ZoneOffset> OFFSET = new TemporalQuery<>() {
392 @Override
393 public ZoneOffset queryFrom(TemporalAccessor temporal) {
394 if (temporal.isSupported(OFFSET_SECONDS)) {
395 return ZoneOffset.ofTotalSeconds(temporal.get(OFFSET_SECONDS));
396 }
397 return null;
398 }
399
400 @Override
401 public String toString() {
402 return "ZoneOffset";
403 }
404 };
405
406 /**
407 * A lenient query for the {@code ZoneId}, falling back to the {@code ZoneOffset}.
408 */
409 static final TemporalQuery<ZoneId> ZONE = new TemporalQuery<>() {
410 @Override
411 public ZoneId queryFrom(TemporalAccessor temporal) {
412 ZoneId zone = temporal.query(ZONE_ID);
413 return (zone != null ? zone : temporal.query(OFFSET));
414 }
415
416 @Override
417 public String toString() {
418 return "Zone";
419 }
420 };
421
422 /**
423 * A query for {@code LocalDate} returning null if not found.
424 */
425 static final TemporalQuery<LocalDate> LOCAL_DATE = new TemporalQuery<>() {
426 @Override
427 public LocalDate queryFrom(TemporalAccessor temporal) {
428 if (temporal.isSupported(EPOCH_DAY)) {
429 return LocalDate.ofEpochDay(temporal.getLong(EPOCH_DAY));
430 }
431 return null;
432 }
433
434 @Override
435 public String toString() {
436 return "LocalDate";
437 }
438 };
439
440 /**
441 * A query for {@code LocalTime} returning null if not found.
442 */
443 static final TemporalQuery<LocalTime> LOCAL_TIME = new TemporalQuery<>() {
444 @Override
445 public LocalTime queryFrom(TemporalAccessor temporal) {
446 if (temporal.isSupported(NANO_OF_DAY)) {
447 return LocalTime.ofNanoOfDay(temporal.getLong(NANO_OF_DAY));
448 }
449 return null;
450 }
451
452 @Override
453 public String toString() {
454 return "LocalTime";
455 }
456 };
457
458 }
459