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).
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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 *
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
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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.chrono;
63
64 import static java.time.temporal.ChronoField.EPOCH_DAY;
65 import static java.time.temporal.ChronoField.ERA;
66 import static java.time.temporal.ChronoField.YEAR;
67 import static java.time.temporal.ChronoUnit.DAYS;
68
69 import java.time.DateTimeException;
70 import java.time.LocalDate;
71 import java.time.LocalTime;
72 import java.time.format.DateTimeFormatter;
73 import java.time.temporal.ChronoField;
74 import java.time.temporal.ChronoUnit;
75 import java.time.temporal.Temporal;
76 import java.time.temporal.TemporalAccessor;
77 import java.time.temporal.TemporalAdjuster;
78 import java.time.temporal.TemporalAmount;
79 import java.time.temporal.TemporalField;
80 import java.time.temporal.TemporalQueries;
81 import java.time.temporal.TemporalQuery;
82 import java.time.temporal.TemporalUnit;
83 import java.time.temporal.UnsupportedTemporalTypeException;
84 import java.util.Comparator;
85 import java.util.Objects;
86
87 /**
88 * A date without time-of-day or time-zone in an arbitrary chronology, intended
89 * for advanced globalization use cases.
90 * <p>
91 * <b>Most applications should declare method signatures, fields and variables
92 * as {@link LocalDate}, not this interface.</b>
93 * <p>
94 * A {@code ChronoLocalDate} is the abstract representation of a date where the
95 * {@code Chronology chronology}, or calendar system, is pluggable.
96 * The date is defined in terms of fields expressed by {@link TemporalField},
97 * where most common implementations are defined in {@link ChronoField}.
98 * The chronology defines how the calendar system operates and the meaning of
99 * the standard fields.
100 *
101 * <h3>When to use this interface</h3>
102 * The design of the API encourages the use of {@code LocalDate} rather than this
103 * interface, even in the case where the application needs to deal with multiple
104 * calendar systems.
105 * <p>
106 * This concept can seem surprising at first, as the natural way to globalize an
107 * application might initially appear to be to abstract the calendar system.
108 * However, as explored below, abstracting the calendar system is usually the wrong
109 * approach, resulting in logic errors and hard to find bugs.
110 * As such, it should be considered an application-wide architectural decision to choose
111 * to use this interface as opposed to {@code LocalDate}.
112 *
113 * <h3>Architectural issues to consider</h3>
114 * These are some of the points that must be considered before using this interface
115 * throughout an application.
116 * <p>
117 * 1) Applications using this interface, as opposed to using just {@code LocalDate},
118 * face a significantly higher probability of bugs. This is because the calendar system
119 * in use is not known at development time. A key cause of bugs is where the developer
120 * applies assumptions from their day-to-day knowledge of the ISO calendar system
121 * to code that is intended to deal with any arbitrary calendar system.
122 * The section below outlines how those assumptions can cause problems
123 * The primary mechanism for reducing this increased risk of bugs is a strong code review process.
124 * This should also be considered a extra cost in maintenance for the lifetime of the code.
125 * <p>
126 * 2) This interface does not enforce immutability of implementations.
127 * While the implementation notes indicate that all implementations must be immutable
128 * there is nothing in the code or type system to enforce this. Any method declared
129 * to accept a {@code ChronoLocalDate} could therefore be passed a poorly or
130 * maliciously written mutable implementation.
131 * <p>
132 * 3) Applications using this interface must consider the impact of eras.
133 * {@code LocalDate} shields users from the concept of eras, by ensuring that {@code getYear()}
134 * returns the proleptic year. That decision ensures that developers can think of
135 * {@code LocalDate} instances as consisting of three fields - year, month-of-year and day-of-month.
136 * By contrast, users of this interface must think of dates as consisting of four fields -
137 * era, year-of-era, month-of-year and day-of-month. The extra era field is frequently
138 * forgotten, yet it is of vital importance to dates in an arbitrary calendar system.
139 * For example, in the Japanese calendar system, the era represents the reign of an Emperor.
140 * Whenever one reign ends and another starts, the year-of-era is reset to one.
141 * <p>
142 * 4) The only agreed international standard for passing a date between two systems
143 * is the ISO-8601 standard which requires the ISO calendar system. Using this interface
144 * throughout the application will inevitably lead to the requirement to pass the date
145 * across a network or component boundary, requiring an application specific protocol or format.
146 * <p>
147 * 5) Long term persistence, such as a database, will almost always only accept dates in the
148 * ISO-8601 calendar system (or the related Julian-Gregorian). Passing around dates in other
149 * calendar systems increases the complications of interacting with persistence.
150 * <p>
151 * 6) Most of the time, passing a {@code ChronoLocalDate} throughout an application
152 * is unnecessary, as discussed in the last section below.
153 *
154 * <h3>False assumptions causing bugs in multi-calendar system code</h3>
155 * As indicated above, there are many issues to consider when try to use and manipulate a
156 * date in an arbitrary calendar system. These are some of the key issues.
157 * <p>
158 * Code that queries the day-of-month and assumes that the value will never be more than
159 * 31 is invalid. Some calendar systems have more than 31 days in some months.
160 * <p>
161 * Code that adds 12 months to a date and assumes that a year has been added is invalid.
162 * Some calendar systems have a different number of months, such as 13 in the Coptic or Ethiopic.
163 * <p>
164 * Code that adds one month to a date and assumes that the month-of-year value will increase
165 * by one or wrap to the next year is invalid. Some calendar systems have a variable number
166 * of months in a year, such as the Hebrew.
167 * <p>
168 * Code that adds one month, then adds a second one month and assumes that the day-of-month
169 * will remain close to its original value is invalid. Some calendar systems have a large difference
170 * between the length of the longest month and the length of the shortest month.
171 * For example, the Coptic or Ethiopic have 12 months of 30 days and 1 month of 5 days.
172 * <p>
173 * Code that adds seven days and assumes that a week has been added is invalid.
174 * Some calendar systems have weeks of other than seven days, such as the French Revolutionary.
175 * <p>
176 * Code that assumes that because the year of {@code date1} is greater than the year of {@code date2}
177 * then {@code date1} is after {@code date2} is invalid. This is invalid for all calendar systems
178 * when referring to the year-of-era, and especially untrue of the Japanese calendar system
179 * where the year-of-era restarts with the reign of every new Emperor.
180 * <p>
181 * Code that treats month-of-year one and day-of-month one as the start of the year is invalid.
182 * Not all calendar systems start the year when the month value is one.
183 * <p>
184 * In general, manipulating a date, and even querying a date, is wide open to bugs when the
185 * calendar system is unknown at development time. This is why it is essential that code using
186 * this interface is subjected to additional code reviews. It is also why an architectural
187 * decision to avoid this interface type is usually the correct one.
188 *
189 * <h3>Using LocalDate instead</h3>
190 * The primary alternative to using this interface throughout your application is as follows.
191 * <ul>
192 * <li>Declare all method signatures referring to dates in terms of {@code LocalDate}.
193 * <li>Either store the chronology (calendar system) in the user profile or lookup
194 * the chronology from the user locale
195 * <li>Convert the ISO {@code LocalDate} to and from the user's preferred calendar system during
196 * printing and parsing
197 * </ul>
198 * This approach treats the problem of globalized calendar systems as a localization issue
199 * and confines it to the UI layer. This approach is in keeping with other localization
200 * issues in the java platform.
201 * <p>
202 * As discussed above, performing calculations on a date where the rules of the calendar system
203 * are pluggable requires skill and is not recommended.
204 * Fortunately, the need to perform calculations on a date in an arbitrary calendar system
205 * is extremely rare. For example, it is highly unlikely that the business rules of a library
206 * book rental scheme will allow rentals to be for one month, where meaning of the month
207 * is dependent on the user's preferred calendar system.
208 * <p>
209 * A key use case for calculations on a date in an arbitrary calendar system is producing
210 * a month-by-month calendar for display and user interaction. Again, this is a UI issue,
211 * and use of this interface solely within a few methods of the UI layer may be justified.
212 * <p>
213 * In any other part of the system, where a date must be manipulated in a calendar system
214 * other than ISO, the use case will generally specify the calendar system to use.
215 * For example, an application may need to calculate the next Islamic or Hebrew holiday
216 * which may require manipulating the date.
217 * This kind of use case can be handled as follows:
218 * <ul>
219 * <li>start from the ISO {@code LocalDate} being passed to the method
220 * <li>convert the date to the alternate calendar system, which for this use case is known
221 * rather than arbitrary
222 * <li>perform the calculation
223 * <li>convert back to {@code LocalDate}
224 * </ul>
225 * Developers writing low-level frameworks or libraries should also avoid this interface.
226 * Instead, one of the two general purpose access interfaces should be used.
227 * Use {@link TemporalAccessor} if read-only access is required, or use {@link Temporal}
228 * if read-write access is required.
229 *
230 * @implSpec
231 * This interface must be implemented with care to ensure other classes operate correctly.
232 * All implementations that can be instantiated must be final, immutable and thread-safe.
233 * Subclasses should be Serializable wherever possible.
234 * <p>
235 * Additional calendar systems may be added to the system.
236 * See {@link Chronology} for more details.
237 *
238 * @since 1.8
239 */
240 public interface ChronoLocalDate
241 extends Temporal, TemporalAdjuster, Comparable<ChronoLocalDate> {
242
243 /**
244 * Gets a comparator that compares {@code ChronoLocalDate} in
245 * time-line order ignoring the chronology.
246 * <p>
247 * This comparator differs from the comparison in {@link #compareTo} in that it
248 * only compares the underlying date and not the chronology.
249 * This allows dates in different calendar systems to be compared based
250 * on the position of the date on the local time-line.
251 * The underlying comparison is equivalent to comparing the epoch-day.
252 *
253 * @return a comparator that compares in time-line order ignoring the chronology
254 * @see #isAfter
255 * @see #isBefore
256 * @see #isEqual
257 */
258 static Comparator<ChronoLocalDate> timeLineOrder() {
259 return AbstractChronology.DATE_ORDER;
260 }
261
262 //-----------------------------------------------------------------------
263 /**
264 * Obtains an instance of {@code ChronoLocalDate} from a temporal object.
265 * <p>
266 * This obtains a local date based on the specified temporal.
267 * A {@code TemporalAccessor} represents an arbitrary set of date and time information,
268 * which this factory converts to an instance of {@code ChronoLocalDate}.
269 * <p>
270 * The conversion extracts and combines the chronology and the date
271 * from the temporal object. The behavior is equivalent to using
272 * {@link Chronology#date(TemporalAccessor)} with the extracted chronology.
273 * Implementations are permitted to perform optimizations such as accessing
274 * those fields that are equivalent to the relevant objects.
275 * <p>
276 * This method matches the signature of the functional interface {@link TemporalQuery}
277 * allowing it to be used as a query via method reference, {@code ChronoLocalDate::from}.
278 *
279 * @param temporal the temporal object to convert, not null
280 * @return the date, not null
281 * @throws DateTimeException if unable to convert to a {@code ChronoLocalDate}
282 * @see Chronology#date(TemporalAccessor)
283 */
284 static ChronoLocalDate from(TemporalAccessor temporal) {
285 if (temporal instanceof ChronoLocalDate) {
286 return (ChronoLocalDate) temporal;
287 }
288 Objects.requireNonNull(temporal, "temporal");
289 Chronology chrono = temporal.query(TemporalQueries.chronology());
290 if (chrono == null) {
291 throw new DateTimeException("Unable to obtain ChronoLocalDate from TemporalAccessor: " + temporal.getClass());
292 }
293 return chrono.date(temporal);
294 }
295
296 //-----------------------------------------------------------------------
297 /**
298 * Gets the chronology of this date.
299 * <p>
300 * The {@code Chronology} represents the calendar system in use.
301 * The era and other fields in {@link ChronoField} are defined by the chronology.
302 *
303 * @return the chronology, not null
304 */
305 Chronology getChronology();
306
307 /**
308 * Gets the era, as defined by the chronology.
309 * <p>
310 * The era is, conceptually, the largest division of the time-line.
311 * Most calendar systems have a single epoch dividing the time-line into two eras.
312 * However, some have multiple eras, such as one for the reign of each leader.
313 * The exact meaning is determined by the {@code Chronology}.
314 * <p>
315 * All correctly implemented {@code Era} classes are singletons, thus it
316 * is valid code to write {@code date.getEra() == SomeChrono.ERA_NAME)}.
317 * <p>
318 * This default implementation uses {@link Chronology#eraOf(int)}.
319 *
320 * @return the chronology specific era constant applicable at this date, not null
321 */
322 default Era getEra() {
323 return getChronology().eraOf(get(ERA));
324 }
325
326 /**
327 * Checks if the year is a leap year, as defined by the calendar system.
328 * <p>
329 * A leap-year is a year of a longer length than normal.
330 * The exact meaning is determined by the chronology with the constraint that
331 * a leap-year must imply a year-length longer than a non leap-year.
332 * <p>
333 * This default implementation uses {@link Chronology#isLeapYear(long)}.
334 *
335 * @return true if this date is in a leap year, false otherwise
336 */
337 default boolean isLeapYear() {
338 return getChronology().isLeapYear(getLong(YEAR));
339 }
340
341 /**
342 * Returns the length of the month represented by this date, as defined by the calendar system.
343 * <p>
344 * This returns the length of the month in days.
345 *
346 * @return the length of the month in days
347 */
348 int lengthOfMonth();
349
350 /**
351 * Returns the length of the year represented by this date, as defined by the calendar system.
352 * <p>
353 * This returns the length of the year in days.
354 * <p>
355 * The default implementation uses {@link #isLeapYear()} and returns 365 or 366.
356 *
357 * @return the length of the year in days
358 */
359 default int lengthOfYear() {
360 return (isLeapYear() ? 366 : 365);
361 }
362
363 /**
364 * Checks if the specified field is supported.
365 * <p>
366 * This checks if the specified field can be queried on this date.
367 * If false, then calling the {@link #range(TemporalField) range},
368 * {@link #get(TemporalField) get} and {@link #with(TemporalField, long)}
369 * methods will throw an exception.
370 * <p>
371 * The set of supported fields is defined by the chronology and normally includes
372 * all {@code ChronoField} date fields.
373 * <p>
374 * If the field is not a {@code ChronoField}, then the result of this method
375 * is obtained by invoking {@code TemporalField.isSupportedBy(TemporalAccessor)}
376 * passing {@code this} as the argument.
377 * Whether the field is supported is determined by the field.
378 *
379 * @param field the field to check, null returns false
380 * @return true if the field can be queried, false if not
381 */
382 @Override
383 default boolean isSupported(TemporalField field) {
384 if (field instanceof ChronoField) {
385 return field.isDateBased();
386 }
387 return field != null && field.isSupportedBy(this);
388 }
389
390 /**
391 * Checks if the specified unit is supported.
392 * <p>
393 * This checks if the specified unit can be added to or subtracted from this date.
394 * If false, then calling the {@link #plus(long, TemporalUnit)} and
395 * {@link #minus(long, TemporalUnit) minus} methods will throw an exception.
396 * <p>
397 * The set of supported units is defined by the chronology and normally includes
398 * all {@code ChronoUnit} date units except {@code FOREVER}.
399 * <p>
400 * If the unit is not a {@code ChronoUnit}, then the result of this method
401 * is obtained by invoking {@code TemporalUnit.isSupportedBy(Temporal)}
402 * passing {@code this} as the argument.
403 * Whether the unit is supported is determined by the unit.
404 *
405 * @param unit the unit to check, null returns false
406 * @return true if the unit can be added/subtracted, false if not
407 */
408 @Override
409 default boolean isSupported(TemporalUnit unit) {
410 if (unit instanceof ChronoUnit) {
411 return unit.isDateBased();
412 }
413 return unit != null && unit.isSupportedBy(this);
414 }
415
416 //-----------------------------------------------------------------------
417 // override for covariant return type
418 /**
419 * {@inheritDoc}
420 * @throws DateTimeException {@inheritDoc}
421 * @throws ArithmeticException {@inheritDoc}
422 */
423 @Override
424 default ChronoLocalDate with(TemporalAdjuster adjuster) {
425 return ChronoLocalDateImpl.ensureValid(getChronology(), Temporal.super.with(adjuster));
426 }
427
428 /**
429 * {@inheritDoc}
430 * @throws DateTimeException {@inheritDoc}
431 * @throws UnsupportedTemporalTypeException {@inheritDoc}
432 * @throws ArithmeticException {@inheritDoc}
433 */
434 @Override
435 default ChronoLocalDate with(TemporalField field, long newValue) {
436 if (field instanceof ChronoField) {
437 throw new UnsupportedTemporalTypeException("Unsupported field: " + field);
438 }
439 return ChronoLocalDateImpl.ensureValid(getChronology(), field.adjustInto(this, newValue));
440 }
441
442 /**
443 * {@inheritDoc}
444 * @throws DateTimeException {@inheritDoc}
445 * @throws ArithmeticException {@inheritDoc}
446 */
447 @Override
448 default ChronoLocalDate plus(TemporalAmount amount) {
449 return ChronoLocalDateImpl.ensureValid(getChronology(), Temporal.super.plus(amount));
450 }
451
452 /**
453 * {@inheritDoc}
454 * @throws DateTimeException {@inheritDoc}
455 * @throws ArithmeticException {@inheritDoc}
456 */
457 @Override
458 default ChronoLocalDate plus(long amountToAdd, TemporalUnit unit) {
459 if (unit instanceof ChronoUnit) {
460 throw new UnsupportedTemporalTypeException("Unsupported unit: " + unit);
461 }
462 return ChronoLocalDateImpl.ensureValid(getChronology(), unit.addTo(this, amountToAdd));
463 }
464
465 /**
466 * {@inheritDoc}
467 * @throws DateTimeException {@inheritDoc}
468 * @throws ArithmeticException {@inheritDoc}
469 */
470 @Override
471 default ChronoLocalDate minus(TemporalAmount amount) {
472 return ChronoLocalDateImpl.ensureValid(getChronology(), Temporal.super.minus(amount));
473 }
474
475 /**
476 * {@inheritDoc}
477 * @throws DateTimeException {@inheritDoc}
478 * @throws UnsupportedTemporalTypeException {@inheritDoc}
479 * @throws ArithmeticException {@inheritDoc}
480 */
481 @Override
482 default ChronoLocalDate minus(long amountToSubtract, TemporalUnit unit) {
483 return ChronoLocalDateImpl.ensureValid(getChronology(), Temporal.super.minus(amountToSubtract, unit));
484 }
485
486 //-----------------------------------------------------------------------
487 /**
488 * Queries this date using the specified query.
489 * <p>
490 * This queries this date using the specified query strategy object.
491 * The {@code TemporalQuery} object defines the logic to be used to
492 * obtain the result. Read the documentation of the query to understand
493 * what the result of this method will be.
494 * <p>
495 * The result of this method is obtained by invoking the
496 * {@link TemporalQuery#queryFrom(TemporalAccessor)} method on the
497 * specified query passing {@code this} as the argument.
498 *
499 * @param <R> the type of the result
500 * @param query the query to invoke, not null
501 * @return the query result, null may be returned (defined by the query)
502 * @throws DateTimeException if unable to query (defined by the query)
503 * @throws ArithmeticException if numeric overflow occurs (defined by the query)
504 */
505 @SuppressWarnings("unchecked")
506 @Override
507 default <R> R query(TemporalQuery<R> query) {
508 if (query == TemporalQueries.zoneId() || query == TemporalQueries.zone() || query == TemporalQueries.offset()) {
509 return null;
510 } else if (query == TemporalQueries.localTime()) {
511 return null;
512 } else if (query == TemporalQueries.chronology()) {
513 return (R) getChronology();
514 } else if (query == TemporalQueries.precision()) {
515 return (R) DAYS;
516 }
517 // inline TemporalAccessor.super.query(query) as an optimization
518 // non-JDK classes are not permitted to make this optimization
519 return query.queryFrom(this);
520 }
521
522 /**
523 * Adjusts the specified temporal object to have the same date as this object.
524 * <p>
525 * This returns a temporal object of the same observable type as the input
526 * with the date changed to be the same as this.
527 * <p>
528 * The adjustment is equivalent to using {@link Temporal#with(TemporalField, long)}
529 * passing {@link ChronoField#EPOCH_DAY} as the field.
530 * <p>
531 * In most cases, it is clearer to reverse the calling pattern by using
532 * {@link Temporal#with(TemporalAdjuster)}:
533 * <pre>
534 * // these two lines are equivalent, but the second approach is recommended
535 * temporal = thisLocalDate.adjustInto(temporal);
536 * temporal = temporal.with(thisLocalDate);
537 * </pre>
538 * <p>
539 * This instance is immutable and unaffected by this method call.
540 *
541 * @param temporal the target object to be adjusted, not null
542 * @return the adjusted object, not null
543 * @throws DateTimeException if unable to make the adjustment
544 * @throws ArithmeticException if numeric overflow occurs
545 */
546 @Override
547 default Temporal adjustInto(Temporal temporal) {
548 return temporal.with(EPOCH_DAY, toEpochDay());
549 }
550
551 /**
552 * Calculates the amount of time until another date in terms of the specified unit.
553 * <p>
554 * This calculates the amount of time between two {@code ChronoLocalDate}
555 * objects in terms of a single {@code TemporalUnit}.
556 * The start and end points are {@code this} and the specified date.
557 * The result will be negative if the end is before the start.
558 * The {@code Temporal} passed to this method is converted to a
559 * {@code ChronoLocalDate} using {@link Chronology#date(TemporalAccessor)}.
560 * The calculation returns a whole number, representing the number of
561 * complete units between the two dates.
562 * For example, the amount in days between two dates can be calculated
563 * using {@code startDate.until(endDate, DAYS)}.
564 * <p>
565 * There are two equivalent ways of using this method.
566 * The first is to invoke this method.
567 * The second is to use {@link TemporalUnit#between(Temporal, Temporal)}:
568 * <pre>
569 * // these two lines are equivalent
570 * amount = start.until(end, MONTHS);
571 * amount = MONTHS.between(start, end);
572 * </pre>
573 * The choice should be made based on which makes the code more readable.
574 * <p>
575 * The calculation is implemented in this method for {@link ChronoUnit}.
576 * The units {@code DAYS}, {@code WEEKS}, {@code MONTHS}, {@code YEARS},
577 * {@code DECADES}, {@code CENTURIES}, {@code MILLENNIA} and {@code ERAS}
578 * should be supported by all implementations.
579 * Other {@code ChronoUnit} values will throw an exception.
580 * <p>
581 * If the unit is not a {@code ChronoUnit}, then the result of this method
582 * is obtained by invoking {@code TemporalUnit.between(Temporal, Temporal)}
583 * passing {@code this} as the first argument and the converted input temporal as
584 * the second argument.
585 * <p>
586 * This instance is immutable and unaffected by this method call.
587 *
588 * @param endExclusive the end date, exclusive, which is converted to a
589 * {@code ChronoLocalDate} in the same chronology, not null
590 * @param unit the unit to measure the amount in, not null
591 * @return the amount of time between this date and the end date
592 * @throws DateTimeException if the amount cannot be calculated, or the end
593 * temporal cannot be converted to a {@code ChronoLocalDate}
594 * @throws UnsupportedTemporalTypeException if the unit is not supported
595 * @throws ArithmeticException if numeric overflow occurs
596 */
597 @Override // override for Javadoc
598 long until(Temporal endExclusive, TemporalUnit unit);
599
600 /**
601 * Calculates the period between this date and another date as a {@code ChronoPeriod}.
602 * <p>
603 * This calculates the period between two dates. All supplied chronologies
604 * calculate the period using years, months and days, however the
605 * {@code ChronoPeriod} API allows the period to be represented using other units.
606 * <p>
607 * The start and end points are {@code this} and the specified date.
608 * The result will be negative if the end is before the start.
609 * The negative sign will be the same in each of year, month and day.
610 * <p>
611 * The calculation is performed using the chronology of this date.
612 * If necessary, the input date will be converted to match.
613 * <p>
614 * This instance is immutable and unaffected by this method call.
615 *
616 * @param endDateExclusive the end date, exclusive, which may be in any chronology, not null
617 * @return the period between this date and the end date, not null
618 * @throws DateTimeException if the period cannot be calculated
619 * @throws ArithmeticException if numeric overflow occurs
620 */
621 ChronoPeriod until(ChronoLocalDate endDateExclusive);
622
623 /**
624 * Formats this date using the specified formatter.
625 * <p>
626 * This date will be passed to the formatter to produce a string.
627 * <p>
628 * The default implementation must behave as follows:
629 * <pre>
630 * return formatter.format(this);
631 * </pre>
632 *
633 * @param formatter the formatter to use, not null
634 * @return the formatted date string, not null
635 * @throws DateTimeException if an error occurs during printing
636 */
637 default String format(DateTimeFormatter formatter) {
638 Objects.requireNonNull(formatter, "formatter");
639 return formatter.format(this);
640 }
641
642 //-----------------------------------------------------------------------
643 /**
644 * Combines this date with a time to create a {@code ChronoLocalDateTime}.
645 * <p>
646 * This returns a {@code ChronoLocalDateTime} formed from this date at the specified time.
647 * All possible combinations of date and time are valid.
648 *
649 * @param localTime the local time to use, not null
650 * @return the local date-time formed from this date and the specified time, not null
651 */
652 @SuppressWarnings("unchecked")
653 default ChronoLocalDateTime<?> atTime(LocalTime localTime) {
654 return ChronoLocalDateTimeImpl.of(this, localTime);
655 }
656
657 //-----------------------------------------------------------------------
658 /**
659 * Converts this date to the Epoch Day.
660 * <p>
661 * The {@link ChronoField#EPOCH_DAY Epoch Day count} is a simple
662 * incrementing count of days where day 0 is 1970-01-01 (ISO).
663 * This definition is the same for all chronologies, enabling conversion.
664 * <p>
665 * This default implementation queries the {@code EPOCH_DAY} field.
666 *
667 * @return the Epoch Day equivalent to this date
668 */
669 default long toEpochDay() {
670 return getLong(EPOCH_DAY);
671 }
672
673 //-----------------------------------------------------------------------
674 /**
675 * Compares this date to another date, including the chronology.
676 * <p>
677 * The comparison is based first on the underlying time-line date, then
678 * on the chronology.
679 * It is "consistent with equals", as defined by {@link Comparable}.
680 * <p>
681 * For example, the following is the comparator order:
682 * <ol>
683 * <li>{@code 2012-12-03 (ISO)}</li>
684 * <li>{@code 2012-12-04 (ISO)}</li>
685 * <li>{@code 2555-12-04 (ThaiBuddhist)}</li>
686 * <li>{@code 2012-12-05 (ISO)}</li>
687 * </ol>
688 * Values #2 and #3 represent the same date on the time-line.
689 * When two values represent the same date, the chronology ID is compared to distinguish them.
690 * This step is needed to make the ordering "consistent with equals".
691 * <p>
692 * If all the date objects being compared are in the same chronology, then the
693 * additional chronology stage is not required and only the local date is used.
694 * To compare the dates of two {@code TemporalAccessor} instances, including dates
695 * in two different chronologies, use {@link ChronoField#EPOCH_DAY} as a comparator.
696 * <p>
697 * This default implementation performs the comparison defined above.
698 *
699 * @param other the other date to compare to, not null
700 * @return the comparator value, negative if less, positive if greater
701 */
702 @Override
703 default int compareTo(ChronoLocalDate other) {
704 int cmp = Long.compare(toEpochDay(), other.toEpochDay());
705 if (cmp == 0) {
706 cmp = getChronology().compareTo(other.getChronology());
707 }
708 return cmp;
709 }
710
711 /**
712 * Checks if this date is after the specified date ignoring the chronology.
713 * <p>
714 * This method differs from the comparison in {@link #compareTo} in that it
715 * only compares the underlying date and not the chronology.
716 * This allows dates in different calendar systems to be compared based
717 * on the time-line position.
718 * This is equivalent to using {@code date1.toEpochDay() > date2.toEpochDay()}.
719 * <p>
720 * This default implementation performs the comparison based on the epoch-day.
721 *
722 * @param other the other date to compare to, not null
723 * @return true if this is after the specified date
724 */
725 default boolean isAfter(ChronoLocalDate other) {
726 return this.toEpochDay() > other.toEpochDay();
727 }
728
729 /**
730 * Checks if this date is before the specified date ignoring the chronology.
731 * <p>
732 * This method differs from the comparison in {@link #compareTo} in that it
733 * only compares the underlying date and not the chronology.
734 * This allows dates in different calendar systems to be compared based
735 * on the time-line position.
736 * This is equivalent to using {@code date1.toEpochDay() < date2.toEpochDay()}.
737 * <p>
738 * This default implementation performs the comparison based on the epoch-day.
739 *
740 * @param other the other date to compare to, not null
741 * @return true if this is before the specified date
742 */
743 default boolean isBefore(ChronoLocalDate other) {
744 return this.toEpochDay() < other.toEpochDay();
745 }
746
747 /**
748 * Checks if this date is equal to the specified date ignoring the chronology.
749 * <p>
750 * This method differs from the comparison in {@link #compareTo} in that it
751 * only compares the underlying date and not the chronology.
752 * This allows dates in different calendar systems to be compared based
753 * on the time-line position.
754 * This is equivalent to using {@code date1.toEpochDay() == date2.toEpochDay()}.
755 * <p>
756 * This default implementation performs the comparison based on the epoch-day.
757 *
758 * @param other the other date to compare to, not null
759 * @return true if the underlying date is equal to the specified date
760 */
761 default boolean isEqual(ChronoLocalDate other) {
762 return this.toEpochDay() == other.toEpochDay();
763 }
764
765 //-----------------------------------------------------------------------
766 /**
767 * Checks if this date is equal to another date, including the chronology.
768 * <p>
769 * Compares this date with another ensuring that the date and chronology are the same.
770 * <p>
771 * To compare the dates of two {@code TemporalAccessor} instances, including dates
772 * in two different chronologies, use {@link ChronoField#EPOCH_DAY} as a comparator.
773 *
774 * @param obj the object to check, null returns false
775 * @return true if this is equal to the other date
776 */
777 @Override
778 boolean equals(Object obj);
779
780 /**
781 * A hash code for this date.
782 *
783 * @return a suitable hash code
784 */
785 @Override
786 int hashCode();
787
788 //-----------------------------------------------------------------------
789 /**
790 * Outputs this date as a {@code String}.
791 * <p>
792 * The output will include the full local date.
793 *
794 * @return the formatted date, not null
795 */
796 @Override
797 String toString();
798
799 }