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26  /*
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32   * Copyright (c) 2012, Stephen Colebourne & Michael Nascimento Santos
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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. The rationale for this is explored in the following documentation.
105  * <p>
106  * The primary use case where this interface should be used is where the generic
107  * type parameter {@code <D>} is fully defined as a specific chronology.
108  * In that case, the assumptions of that chronology are known at development
109  * time and specified in the code.
110  * <p>
111  * When the chronology is defined in the generic type parameter as ? or otherwise
112  * unknown at development time, the rest of the discussion below applies.
113  * <p>
114  * To emphasize the point, declaring a method signature, field or variable as this
115  * interface type can initially seem like the sensible way to globalize an application,
116  * however it is usually the wrong approach.
117  * As such, it should be considered an application-wide architectural decision to choose
118  * to use this interface as opposed to {@code LocalDate}.
119  *
120  * <h3>Architectural issues to consider</h3>
121  * These are some of the points that must be considered before using this interface
122  * throughout an application.
123  * <p>
124  * 1) Applications using this interface, as opposed to using just {@code LocalDate},
125  * face a significantly higher probability of bugs. This is because the calendar system
126  * in use is not known at development time. A key cause of bugs is where the developer
127  * applies assumptions from their day-to-day knowledge of the ISO calendar system
128  * to code that is intended to deal with any arbitrary calendar system.
129  * The section below outlines how those assumptions can cause problems
130  * The primary mechanism for reducing this increased risk of bugs is a strong code review process.
131  * This should also be considered a extra cost in maintenance for the lifetime of the code.
132  * <p>
133  * 2) This interface does not enforce immutability of implementations.
134  * While the implementation notes indicate that all implementations must be immutable
135  * there is nothing in the code or type system to enforce this. Any method declared
136  * to accept a {@code ChronoLocalDate} could therefore be passed a poorly or
137  * maliciously written mutable implementation.
138  * <p>
139  * 3) Applications using this interface  must consider the impact of eras.
140  * {@code LocalDate} shields users from the concept of eras, by ensuring that {@code getYear()}
141  * returns the proleptic year. That decision ensures that developers can think of
142  * {@code LocalDate} instances as consisting of three fields - year, month-of-year and day-of-month.
143  * By contrast, users of this interface must think of dates as consisting of four fields -
144  * era, year-of-era, month-of-year and day-of-month. The extra era field is frequently
145  * forgotten, yet it is of vital importance to dates in an arbitrary calendar system.
146  * For example, in the Japanese calendar system, the era represents the reign of an Emperor.
147  * Whenever one reign ends and another starts, the year-of-era is reset to one.
148  * <p>
149  * 4) The only agreed international standard for passing a date between two systems
150  * is the ISO-8601 standard which requires the ISO calendar system. Using this interface
151  * throughout the application will inevitably lead to the requirement to pass the date
152  * across a network or component boundary, requiring an application specific protocol or format.
153  * <p>
154  * 5) Long term persistence, such as a database, will almost always only accept dates in the
155  * ISO-8601 calendar system (or the related Julian-Gregorian). Passing around dates in other
156  * calendar systems increases the complications of interacting with persistence.
157  * <p>
158  * 6) Most of the time, passing a {@code ChronoLocalDate} throughout an application
159  * is unnecessary, as discussed in the last section below.
160  *
161  * <h3>False assumptions causing bugs in multi-calendar system code</h3>
162  * As indicated above, there are many issues to consider when try to use and manipulate a
163  * date in an arbitrary calendar system. These are some of the key issues.
164  * <p>
165  * Code that queries the day-of-month and assumes that the value will never be more than
166  * 31 is invalid. Some calendar systems have more than 31 days in some months.
167  * <p>
168  * Code that adds 12 months to a date and assumes that a year has been added is invalid.
169  * Some calendar systems have a different number of months, such as 13 in the Coptic or Ethiopic.
170  * <p>
171  * Code that adds one month to a date and assumes that the month-of-year value will increase
172  * by one or wrap to the next year is invalid. Some calendar systems have a variable number
173  * of months in a year, such as the Hebrew.
174  * <p>
175  * Code that adds one month, then adds a second one month and assumes that the day-of-month
176  * will remain close to its original value is invalid. Some calendar systems have a large difference
177  * between the length of the longest month and the length of the shortest month.
178  * For example, the Coptic or Ethiopic have 12 months of 30 days and 1 month of 5 days.
179  * <p>
180  * Code that adds seven days and assumes that a week has been added is invalid.
181  * Some calendar systems have weeks of other than seven days, such as the French Revolutionary.
182  * <p>
183  * Code that assumes that because the year of {@code date1} is greater than the year of {@code date2}
184  * then {@code date1} is after {@code date2} is invalid. This is invalid for all calendar systems
185  * when referring to the year-of-era, and especially untrue of the Japanese calendar system
186  * where the year-of-era restarts with the reign of every new Emperor.
187  * <p>
188  * Code that treats month-of-year one and day-of-month one as the start of the year is invalid.
189  * Not all calendar systems start the year when the month value is one.
190  * <p>
191  * In general, manipulating a date, and even querying a date, is wide open to bugs when the
192  * calendar system is unknown at development time. This is why it is essential that code using
193  * this interface is subjected to additional code reviews. It is also why an architectural
194  * decision to avoid this interface type is usually the correct one.
195  *
196  * <h3>Using LocalDate instead</h3>
197  * The primary alternative to using this interface throughout your application is as follows.
198  * <ul>
199  * <li>Declare all method signatures referring to dates in terms of {@code LocalDate}.
200  * <li>Either store the chronology (calendar system) in the user profile or lookup
201  *  the chronology from the user locale
202  * <li>Convert the ISO {@code LocalDate} to and from the user's preferred calendar system during
203  *  printing and parsing
204  * </ul>
205  * This approach treats the problem of globalized calendar systems as a localization issue
206  * and confines it to the UI layer. This approach is in keeping with other localization
207  * issues in the java platform.
208  * <p>
209  * As discussed above, performing calculations on a date where the rules of the calendar system
210  * are pluggable requires skill and is not recommended.
211  * Fortunately, the need to perform calculations on a date in an arbitrary calendar system
212  * is extremely rare. For example, it is highly unlikely that the business rules of a library
213  * book rental scheme will allow rentals to be for one month, where meaning of the month
214  * is dependent on the user's preferred calendar system.
215  * <p>
216  * A key use case for calculations on a date in an arbitrary calendar system is producing
217  * a month-by-month calendar for display and user interaction. Again, this is a UI issue,
218  * and use of this interface solely within a few methods of the UI layer may be justified.
219  * <p>
220  * In any other part of the system, where a date must be manipulated in a calendar system
221  * other than ISO, the use case will generally specify the calendar system to use.
222  * For example, an application may need to calculate the next Islamic or Hebrew holiday
223  * which may require manipulating the date.
224  * This kind of use case can be handled as follows:
225  * <ul>
226  * <li>start from the ISO {@code LocalDate} being passed to the method
227  * <li>convert the date to the alternate calendar system, which for this use case is known
228  *  rather than arbitrary
229  * <li>perform the calculation
230  * <li>convert back to {@code LocalDate}
231  * </ul>
232  * Developers writing low-level frameworks or libraries should also avoid this interface.
233  * Instead, one of the two general purpose access interfaces should be used.
234  * Use {@link TemporalAccessor} if read-only access is required, or use {@link Temporal}
235  * if read-write access is required.
236  *
237  * @implSpec
238  * This interface must be implemented with care to ensure other classes operate correctly.
239  * All implementations that can be instantiated must be final, immutable and thread-safe.
240  * Subclasses should be Serializable wherever possible.
241  * <p>
242  * Additional calendar systems may be added to the system.
243  * See {@link Chronology} for more details.
244  *
245  * @since 1.8
246  */
247 public interface ChronoLocalDate
248         extends Temporal, TemporalAdjuster, Comparable<ChronoLocalDate> {
249 
250     /**
251      * Gets a comparator that compares {@code ChronoLocalDate} in
252      * time-line order ignoring the chronology.
253      * <p>
254      * This comparator differs from the comparison in {@link #compareTo} in that it
255      * only compares the underlying date and not the chronology.
256      * This allows dates in different calendar systems to be compared based
257      * on the position of the date on the local time-line.
258      * The underlying comparison is equivalent to comparing the epoch-day.
259      * @return a comparator that compares in time-line order ignoring the chronology
260      *
261      * @see #isAfter
262      * @see #isBefore
263      * @see #isEqual
264      */
265     static Comparator<ChronoLocalDate> timeLineOrder() {
266         return AbstractChronology.DATE_ORDER;
267     }
268 
269     //-----------------------------------------------------------------------
270     /**
271      * Obtains an instance of {@code ChronoLocalDate} from a temporal object.
272      * <p>
273      * This obtains a local date based on the specified temporal.
274      * A {@code TemporalAccessor} represents an arbitrary set of date and time information,
275      * which this factory converts to an instance of {@code ChronoLocalDate}.
276      * <p>
277      * The conversion extracts and combines the chronology and the date
278      * from the temporal object. The behavior is equivalent to using
279      * {@link Chronology#date(TemporalAccessor)} with the extracted chronology.
280      * Implementations are permitted to perform optimizations such as accessing
281      * those fields that are equivalent to the relevant objects.
282      * <p>
283      * This method matches the signature of the functional interface {@link TemporalQuery}
284      * allowing it to be used as a query via method reference, {@code ChronoLocalDate::from}.
285      *
286      * @param temporal  the temporal object to convert, not null
287      * @return the date, not null
288      * @throws DateTimeException if unable to convert to a {@code ChronoLocalDate}
289      * @see Chronology#date(TemporalAccessor)
290      */
291     static ChronoLocalDate from(TemporalAccessor temporal) {
292         if (temporal instanceof ChronoLocalDate) {
293             return (ChronoLocalDate) temporal;
294         }
295         Objects.requireNonNull(temporal, "temporal");
296         Chronology chrono = temporal.query(TemporalQueries.chronology());
297         if (chrono == null) {
298             throw new DateTimeException("Unable to obtain ChronoLocalDate from TemporalAccessor: " + temporal.getClass());
299         }
300         return chrono.date(temporal);
301     }
302 
303     //-----------------------------------------------------------------------
304     /**
305      * Gets the chronology of this date.
306      * <p>
307      * The {@code Chronology} represents the calendar system in use.
308      * The era and other fields in {@link ChronoField} are defined by the chronology.
309      *
310      * @return the chronology, not null
311      */
312     Chronology getChronology();
313 
314     /**
315      * Gets the era, as defined by the chronology.
316      * <p>
317      * The era is, conceptually, the largest division of the time-line.
318      * Most calendar systems have a single epoch dividing the time-line into two eras.
319      * However, some have multiple eras, such as one for the reign of each leader.
320      * The exact meaning is determined by the {@code Chronology}.
321      * <p>
322      * All correctly implemented {@code Era} classes are singletons, thus it
323      * is valid code to write {@code date.getEra() == SomeChrono.ERA_NAME)}.
324      * <p>
325      * This default implementation uses {@link Chronology#eraOf(int)}.
326      *
327      * @return the chronology specific era constant applicable at this date, not null
328      */
329     default Era getEra() {
330         return getChronology().eraOf(get(ERA));
331     }
332 
333     /**
334      * Checks if the year is a leap year, as defined by the calendar system.
335      * <p>
336      * A leap-year is a year of a longer length than normal.
337      * The exact meaning is determined by the chronology with the constraint that
338      * a leap-year must imply a year-length longer than a non leap-year.
339      * <p>
340      * This default implementation uses {@link Chronology#isLeapYear(long)}.
341      *
342      * @return true if this date is in a leap year, false otherwise
343      */
344     default boolean isLeapYear() {
345         return getChronology().isLeapYear(getLong(YEAR));
346     }
347 
348     /**
349      * Returns the length of the month represented by this date, as defined by the calendar system.
350      * <p>
351      * This returns the length of the month in days.
352      *
353      * @return the length of the month in days
354      */
355     int lengthOfMonth();
356 
357     /**
358      * Returns the length of the year represented by this date, as defined by the calendar system.
359      * <p>
360      * This returns the length of the year in days.
361      * <p>
362      * The default implementation uses {@link #isLeapYear()} and returns 365 or 366.
363      *
364      * @return the length of the year in days
365      */
366     default int lengthOfYear() {
367         return (isLeapYear() ? 366 : 365);
368     }
369 
370     /**
371      * Checks if the specified field is supported.
372      * <p>
373      * This checks if the specified field can be queried on this date.
374      * If false, then calling the {@link #range(TemporalField) range},
375      * {@link #get(TemporalField) get} and {@link #with(TemporalField, long)}
376      * methods will throw an exception.
377      * <p>
378      * The set of supported fields is defined by the chronology and normally includes
379      * all {@code ChronoField} date fields.
380      * <p>
381      * If the field is not a {@code ChronoField}, then the result of this method
382      * is obtained by invoking {@code TemporalField.isSupportedBy(TemporalAccessor)}
383      * passing {@code this} as the argument.
384      * Whether the field is supported is determined by the field.
385      *
386      * @param field  the field to check, null returns false
387      * @return true if the field can be queried, false if not
388      */
389     @Override
390     default boolean isSupported(TemporalField field) {
391         if (field instanceof ChronoField) {
392             return field.isDateBased();
393         }
394         return field != null && field.isSupportedBy(this);
395     }
396 
397     /**
398      * Checks if the specified unit is supported.
399      * <p>
400      * This checks if the specified unit can be added to or subtracted from this date.
401      * If false, then calling the {@link #plus(long, TemporalUnit)} and
402      * {@link #minus(long, TemporalUnit) minus} methods will throw an exception.
403      * <p>
404      * The set of supported units is defined by the chronology and normally includes
405      * all {@code ChronoUnit} date units except {@code FOREVER}.
406      * <p>
407      * If the unit is not a {@code ChronoUnit}, then the result of this method
408      * is obtained by invoking {@code TemporalUnit.isSupportedBy(Temporal)}
409      * passing {@code this} as the argument.
410      * Whether the unit is supported is determined by the unit.
411      *
412      * @param unit  the unit to check, null returns false
413      * @return true if the unit can be added/subtracted, false if not
414      */
415     @Override
416     default boolean isSupported(TemporalUnit unit) {
417         if (unit instanceof ChronoUnit) {
418             return unit.isDateBased();
419         }
420         return unit != null && unit.isSupportedBy(this);
421     }
422 
423     //-----------------------------------------------------------------------
424     // override for covariant return type
425     /**
426      * {@inheritDoc}
427      * @throws DateTimeException {@inheritDoc}
428      * @throws ArithmeticException {@inheritDoc}
429      */
430     @Override
431     default ChronoLocalDate with(TemporalAdjuster adjuster) {
432         return ChronoLocalDateImpl.ensureValid(getChronology(), Temporal.super.with(adjuster));
433     }
434 
435     /**
436      * {@inheritDoc}
437      * @throws DateTimeException {@inheritDoc}
438      * @throws UnsupportedTemporalTypeException {@inheritDoc}
439      * @throws ArithmeticException {@inheritDoc}
440      */
441     @Override
442     default ChronoLocalDate with(TemporalField field, long newValue) {
443         if (field instanceof ChronoField) {
444             throw new UnsupportedTemporalTypeException("Unsupported field: " + field);
445         }
446         return ChronoLocalDateImpl.ensureValid(getChronology(), field.adjustInto(this, newValue));
447     }
448 
449     /**
450      * {@inheritDoc}
451      * @throws DateTimeException {@inheritDoc}
452      * @throws ArithmeticException {@inheritDoc}
453      */
454     @Override
455     default ChronoLocalDate plus(TemporalAmount amount) {
456         return ChronoLocalDateImpl.ensureValid(getChronology(), Temporal.super.plus(amount));
457     }
458 
459     /**
460      * {@inheritDoc}
461      * @throws DateTimeException {@inheritDoc}
462      * @throws ArithmeticException {@inheritDoc}
463      */
464     @Override
465     default ChronoLocalDate plus(long amountToAdd, TemporalUnit unit) {
466         if (unit instanceof ChronoUnit) {
467             throw new UnsupportedTemporalTypeException("Unsupported unit: " + unit);
468         }
469         return ChronoLocalDateImpl.ensureValid(getChronology(), unit.addTo(this, amountToAdd));
470     }
471 
472     /**
473      * {@inheritDoc}
474      * @throws DateTimeException {@inheritDoc}
475      * @throws ArithmeticException {@inheritDoc}
476      */
477     @Override
478     default ChronoLocalDate minus(TemporalAmount amount) {
479         return ChronoLocalDateImpl.ensureValid(getChronology(), Temporal.super.minus(amount));
480     }
481 
482     /**
483      * {@inheritDoc}
484      * @throws DateTimeException {@inheritDoc}
485      * @throws UnsupportedTemporalTypeException {@inheritDoc}
486      * @throws ArithmeticException {@inheritDoc}
487      */
488     @Override
489     default ChronoLocalDate minus(long amountToSubtract, TemporalUnit unit) {
490         return ChronoLocalDateImpl.ensureValid(getChronology(), Temporal.super.minus(amountToSubtract, unit));
491     }
492 
493     //-----------------------------------------------------------------------
494     /**
495      * Queries this date using the specified query.
496      * <p>
497      * This queries this date using the specified query strategy object.
498      * The {@code TemporalQuery} object defines the logic to be used to
499      * obtain the result. Read the documentation of the query to understand
500      * what the result of this method will be.
501      * <p>
502      * The result of this method is obtained by invoking the
503      * {@link TemporalQuery#queryFrom(TemporalAccessor)} method on the
504      * specified query passing {@code this} as the argument.
505      *
506      * @param <R> the type of the result
507      * @param query  the query to invoke, not null
508      * @return the query result, null may be returned (defined by the query)
509      * @throws DateTimeException if unable to query (defined by the query)
510      * @throws ArithmeticException if numeric overflow occurs (defined by the query)
511      */
512     @SuppressWarnings("unchecked")
513     @Override
514     default <R> R query(TemporalQuery<R> query) {
515         if (query == TemporalQueries.zoneId() || query == TemporalQueries.zone() || query == TemporalQueries.offset()) {
516             return null;
517         } else if (query == TemporalQueries.localTime()) {
518             return null;
519         } else if (query == TemporalQueries.chronology()) {
520             return (R) getChronology();
521         } else if (query == TemporalQueries.precision()) {
522             return (R) DAYS;
523         }
524         // inline TemporalAccessor.super.query(query) as an optimization
525         // non-JDK classes are not permitted to make this optimization
526         return query.queryFrom(this);
527     }
528 
529     /**
530      * Adjusts the specified temporal object to have the same date as this object.
531      * <p>
532      * This returns a temporal object of the same observable type as the input
533      * with the date changed to be the same as this.
534      * <p>
535      * The adjustment is equivalent to using {@link Temporal#with(TemporalField, long)}
536      * passing {@link ChronoField#EPOCH_DAY} as the field.
537      * <p>
538      * In most cases, it is clearer to reverse the calling pattern by using
539      * {@link Temporal#with(TemporalAdjuster)}:
540      * <pre>
541      *   // these two lines are equivalent, but the second approach is recommended
542      *   temporal = thisLocalDate.adjustInto(temporal);
543      *   temporal = temporal.with(thisLocalDate);
544      * </pre>
545      * <p>
546      * This instance is immutable and unaffected by this method call.
547      *
548      * @param temporal  the target object to be adjusted, not null
549      * @return the adjusted object, not null
550      * @throws DateTimeException if unable to make the adjustment
551      * @throws ArithmeticException if numeric overflow occurs
552      */
553     @Override
554     default Temporal adjustInto(Temporal temporal) {
555         return temporal.with(EPOCH_DAY, toEpochDay());
556     }
557 
558     /**
559      * Calculates the amount of time until another date in terms of the specified unit.
560      * <p>
561      * This calculates the amount of time between two {@code ChronoLocalDate}
562      * objects in terms of a single {@code TemporalUnit}.
563      * The start and end points are {@code this} and the specified date.
564      * The result will be negative if the end is before the start.
565      * The {@code Temporal} passed to this method is converted to a
566      * {@code ChronoLocalDate} using {@link Chronology#date(TemporalAccessor)}.
567      * The calculation returns a whole number, representing the number of
568      * complete units between the two dates.
569      * For example, the amount in days between two dates can be calculated
570      * using {@code startDate.until(endDate, DAYS)}.
571      * <p>
572      * There are two equivalent ways of using this method.
573      * The first is to invoke this method.
574      * The second is to use {@link TemporalUnit#between(Temporal, Temporal)}:
575      * <pre>
576      *   // these two lines are equivalent
577      *   amount = start.until(end, MONTHS);
578      *   amount = MONTHS.between(start, end);
579      * </pre>
580      * The choice should be made based on which makes the code more readable.
581      * <p>
582      * The calculation is implemented in this method for {@link ChronoUnit}.
583      * The units {@code DAYS}, {@code WEEKS}, {@code MONTHS}, {@code YEARS},
584      * {@code DECADES}, {@code CENTURIES}, {@code MILLENNIA} and {@code ERAS}
585      * should be supported by all implementations.
586      * Other {@code ChronoUnit} values will throw an exception.
587      * <p>
588      * If the unit is not a {@code ChronoUnit}, then the result of this method
589      * is obtained by invoking {@code TemporalUnit.between(Temporal, Temporal)}
590      * passing {@code this} as the first argument and the converted input temporal as
591      * the second argument.
592      * <p>
593      * This instance is immutable and unaffected by this method call.
594      *
595      * @param endExclusive  the end date, exclusive, which is converted to a
596      *  {@code ChronoLocalDate} in the same chronology, not null
597      * @param unit  the unit to measure the amount in, not null
598      * @return the amount of time between this date and the end date
599      * @throws DateTimeException if the amount cannot be calculated, or the end
600      *  temporal cannot be converted to a {@code ChronoLocalDate}
601      * @throws UnsupportedTemporalTypeException if the unit is not supported
602      * @throws ArithmeticException if numeric overflow occurs
603      */
604     @Override  // override for Javadoc
605     long until(Temporal endExclusive, TemporalUnit unit);
606 
607     /**
608      * Calculates the period between this date and another date as a {@code ChronoPeriod}.
609      * <p>
610      * This calculates the period between two dates. All supplied chronologies
611      * calculate the period using years, months and days, however the
612      * {@code ChronoPeriod} API allows the period to be represented using other units.
613      * <p>
614      * The start and end points are {@code this} and the specified date.
615      * The result will be negative if the end is before the start.
616      * The negative sign will be the same in each of year, month and day.
617      * <p>
618      * The calculation is performed using the chronology of this date.
619      * If necessary, the input date will be converted to match.
620      * <p>
621      * This instance is immutable and unaffected by this method call.
622      *
623      * @param endDateExclusive  the end date, exclusive, which may be in any chronology, not null
624      * @return the period between this date and the end date, not null
625      * @throws DateTimeException if the period cannot be calculated
626      * @throws ArithmeticException if numeric overflow occurs
627      */
628     ChronoPeriod until(ChronoLocalDate endDateExclusive);
629 
630     /**
631      * Formats this date using the specified formatter.
632      * <p>
633      * This date will be passed to the formatter to produce a string.
634      * <p>
635      * The default implementation must behave as follows:
636      * <pre>
637      *  return formatter.format(this);
638      * </pre>
639      *
640      * @param formatter  the formatter to use, not null
641      * @return the formatted date string, not null
642      * @throws DateTimeException if an error occurs during printing
643      */
644     default String format(DateTimeFormatter formatter) {
645         Objects.requireNonNull(formatter, "formatter");
646         return formatter.format(this);
647     }
648 
649     //-----------------------------------------------------------------------
650     /**
651      * Combines this date with a time to create a {@code ChronoLocalDateTime}.
652      * <p>
653      * This returns a {@code ChronoLocalDateTime} formed from this date at the specified time.
654      * All possible combinations of date and time are valid.
655      *
656      * @param localTime  the local time to use, not null
657      * @return the local date-time formed from this date and the specified time, not null
658      */
659     @SuppressWarnings("unchecked")
660     default ChronoLocalDateTime<?> atTime(LocalTime localTime) {
661         return ChronoLocalDateTimeImpl.of(this, localTime);
662     }
663 
664     //-----------------------------------------------------------------------
665     /**
666      * Converts this date to the Epoch Day.
667      * <p>
668      * The {@link ChronoField#EPOCH_DAY Epoch Day count} is a simple
669      * incrementing count of days where day 0 is 1970-01-01 (ISO).
670      * This definition is the same for all chronologies, enabling conversion.
671      * <p>
672      * This default implementation queries the {@code EPOCH_DAY} field.
673      *
674      * @return the Epoch Day equivalent to this date
675      */
676     default long toEpochDay() {
677         return getLong(EPOCH_DAY);
678     }
679 
680     //-----------------------------------------------------------------------
681     /**
682      * Compares this date to another date, including the chronology.
683      * <p>
684      * The comparison is based first on the underlying time-line date, then
685      * on the chronology.
686      * It is "consistent with equals", as defined by {@link Comparable}.
687      * <p>
688      * For example, the following is the comparator order:
689      * <ol>
690      * <li>{@code 2012-12-03 (ISO)}</li>
691      * <li>{@code 2012-12-04 (ISO)}</li>
692      * <li>{@code 2555-12-04 (ThaiBuddhist)}</li>
693      * <li>{@code 2012-12-05 (ISO)}</li>
694      * </ol>
695      * Values #2 and #3 represent the same date on the time-line.
696      * When two values represent the same date, the chronology ID is compared to distinguish them.
697      * This step is needed to make the ordering "consistent with equals".
698      * <p>
699      * If all the date objects being compared are in the same chronology, then the
700      * additional chronology stage is not required and only the local date is used.
701      * To compare the dates of two {@code TemporalAccessor} instances, including dates
702      * in two different chronologies, use {@link ChronoField#EPOCH_DAY} as a comparator.
703      * <p>
704      * This default implementation performs the comparison defined above.
705      *
706      * @param other  the other date to compare to, not null
707      * @return the comparator value, negative if less, positive if greater
708      */
709     @Override
710     default int compareTo(ChronoLocalDate other) {
711         int cmp = Long.compare(toEpochDay(), other.toEpochDay());
712         if (cmp == 0) {
713             cmp = getChronology().compareTo(other.getChronology());
714         }
715         return cmp;
716     }
717 
718     /**
719      * Checks if this date is after the specified date ignoring the chronology.
720      * <p>
721      * This method differs from the comparison in {@link #compareTo} in that it
722      * only compares the underlying date and not the chronology.
723      * This allows dates in different calendar systems to be compared based
724      * on the time-line position.
725      * This is equivalent to using {@code date1.toEpochDay() &gt; date2.toEpochDay()}.
726      * <p>
727      * This default implementation performs the comparison based on the epoch-day.
728      *
729      * @param other  the other date to compare to, not null
730      * @return true if this is after the specified date
731      */
732     default boolean isAfter(ChronoLocalDate other) {
733         return this.toEpochDay() > other.toEpochDay();
734     }
735 
736     /**
737      * Checks if this date is before the specified date ignoring the chronology.
738      * <p>
739      * This method differs from the comparison in {@link #compareTo} in that it
740      * only compares the underlying date and not the chronology.
741      * This allows dates in different calendar systems to be compared based
742      * on the time-line position.
743      * This is equivalent to using {@code date1.toEpochDay() &lt; date2.toEpochDay()}.
744      * <p>
745      * This default implementation performs the comparison based on the epoch-day.
746      *
747      * @param other  the other date to compare to, not null
748      * @return true if this is before the specified date
749      */
750     default boolean isBefore(ChronoLocalDate other) {
751         return this.toEpochDay() < other.toEpochDay();
752     }
753 
754     /**
755      * Checks if this date is equal to the specified date ignoring the chronology.
756      * <p>
757      * This method differs from the comparison in {@link #compareTo} in that it
758      * only compares the underlying date and not the chronology.
759      * This allows dates in different calendar systems to be compared based
760      * on the time-line position.
761      * This is equivalent to using {@code date1.toEpochDay() == date2.toEpochDay()}.
762      * <p>
763      * This default implementation performs the comparison based on the epoch-day.
764      *
765      * @param other  the other date to compare to, not null
766      * @return true if the underlying date is equal to the specified date
767      */
768     default boolean isEqual(ChronoLocalDate other) {
769         return this.toEpochDay() == other.toEpochDay();
770     }
771 
772     //-----------------------------------------------------------------------
773     /**
774      * Checks if this date is equal to another date, including the chronology.
775      * <p>
776      * Compares this date with another ensuring that the date and chronology are the same.
777      * <p>
778      * To compare the dates of two {@code TemporalAccessor} instances, including dates
779      * in two different chronologies, use {@link ChronoField#EPOCH_DAY} as a comparator.
780      *
781      * @param obj  the object to check, null returns false
782      * @return true if this is equal to the other date
783      */
784     @Override
785     boolean equals(Object obj);
786 
787     /**
788      * A hash code for this date.
789      *
790      * @return a suitable hash code
791      */
792     @Override
793     int hashCode();
794 
795     //-----------------------------------------------------------------------
796     /**
797      * Outputs this date as a {@code String}.
798      * <p>
799      * The output will include the full local date.
800      *
801      * @return the formatted date, not null
802      */
803     @Override
804     String toString();
805 
806 }