1 /*
2 * Copyright (c) 2012, 2025, 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 *
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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) 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
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;
63
64 import static java.time.temporal.ChronoField.ERA;
65 import static java.time.temporal.ChronoField.MONTH_OF_YEAR;
66 import static java.time.temporal.ChronoField.PROLEPTIC_MONTH;
67 import static java.time.temporal.ChronoField.YEAR;
68 import static java.time.temporal.ChronoField.YEAR_OF_ERA;
69 import static java.time.temporal.ChronoUnit.CENTURIES;
70 import static java.time.temporal.ChronoUnit.DECADES;
71 import static java.time.temporal.ChronoUnit.ERAS;
72 import static java.time.temporal.ChronoUnit.MILLENNIA;
73 import static java.time.temporal.ChronoUnit.MONTHS;
74 import static java.time.temporal.ChronoUnit.YEARS;
75
76 import java.io.DataInput;
77 import java.io.DataOutput;
78 import java.io.IOException;
79 import java.io.InvalidObjectException;
80 import java.io.ObjectInputStream;
81 import java.io.ObjectStreamField;
82 import java.io.Serial;
83 import java.io.Serializable;
84 import java.time.chrono.Chronology;
85 import java.time.chrono.IsoChronology;
86 import java.time.format.DateTimeFormatter;
87 import java.time.format.DateTimeFormatterBuilder;
88 import java.time.format.DateTimeParseException;
89 import java.time.format.SignStyle;
90 import java.time.temporal.ChronoField;
91 import java.time.temporal.ChronoUnit;
92 import java.time.temporal.Temporal;
93 import java.time.temporal.TemporalAccessor;
94 import java.time.temporal.TemporalAdjuster;
95 import java.time.temporal.TemporalAmount;
96 import java.time.temporal.TemporalField;
97 import java.time.temporal.TemporalQueries;
98 import java.time.temporal.TemporalQuery;
99 import java.time.temporal.TemporalUnit;
100 import java.time.temporal.UnsupportedTemporalTypeException;
101 import java.time.temporal.ValueRange;
102 import java.util.Objects;
103
104 import jdk.internal.util.DecimalDigits;
105
106 /**
107 * A year-month in the ISO-8601 calendar system, such as {@code 2007-12}.
108 * <p>
109 * {@code YearMonth} is an immutable date-time object that represents the combination
110 * of a year and month. Any field that can be derived from a year and month, such as
111 * quarter-of-year, can be obtained.
112 * <p>
113 * This class does not store or represent a day, time or time-zone.
114 * For example, the value "October 2007" can be stored in a {@code YearMonth}.
115 * <p>
116 * The ISO-8601 calendar system is the modern civil calendar system used today
117 * in most of the world. It is equivalent to the proleptic Gregorian calendar
118 * system, in which today's rules for leap years are applied for all time.
119 * For most applications written today, the ISO-8601 rules are entirely suitable.
120 * However, any application that makes use of historical dates, and requires them
121 * to be accurate will find the ISO-8601 approach unsuitable.
122 * <p>
123 * This is a <a href="{@docRoot}/java.base/java/lang/doc-files/ValueBased.html">value-based</a>
124 * class; programmers should treat instances that are
125 * {@linkplain #equals(Object) equal} as interchangeable and should not
126 * use instances for synchronization, or unpredictable behavior may
127 * occur. For example, in a future release, synchronization may fail.
128 * The {@code equals} method should be used for comparisons.
129 *
130 * @implSpec
131 * This class is immutable and thread-safe.
132 *
133 * @since 1.8
134 */
135 @jdk.internal.ValueBased
136 public final class YearMonth
137 implements Temporal, TemporalAdjuster, Comparable<YearMonth>, Serializable {
138
139 /**
140 * Serialization version.
141 */
142 @java.io.Serial
143 private static final long serialVersionUID = 4183400860270640070L;
144
145 /**
146 * For backward compatibility of the serialized {@code YearMonth.class} object,
147 * explicitly declare the types of the serialized fields as defined in Java SE 8.
148 * Instances of {@code YearMonth} are serialized using the dedicated
149 * serialized form by {@code writeReplace}.
150 * @serialField year int The year.
151 * @serialField month int The month-of-year.
152 */
153 @java.io.Serial
154 private static final ObjectStreamField[] serialPersistentFields = {
155 new ObjectStreamField("year", int.class),
156 new ObjectStreamField("month", int.class),
157 };
158 /**
159 * Parser.
160 */
161 private static final DateTimeFormatter PARSER = new DateTimeFormatterBuilder()
162 .appendValue(YEAR, 4, 10, SignStyle.EXCEEDS_PAD)
163 .appendLiteral('-')
164 .appendValue(MONTH_OF_YEAR, 2)
165 .toFormatter();
166
167 /**
168 * @serial The year.
169 */
170 private final transient int year;
171 /**
172 * @serial The month-of-year..
173 */
174 private final transient byte month;
175
176 //-----------------------------------------------------------------------
177 /**
178 * Obtains the current year-month from the system clock in the default time-zone.
179 * <p>
180 * This will query the {@link Clock#systemDefaultZone() system clock} in the default
181 * time-zone to obtain the current year-month.
182 * <p>
183 * Using this method will prevent the ability to use an alternate clock for testing
184 * because the clock is hard-coded.
185 *
186 * @return the current year-month using the system clock and default time-zone, not null
187 */
188 public static YearMonth now() {
189 return now(Clock.systemDefaultZone());
190 }
191
192 /**
193 * Obtains the current year-month from the system clock in the specified time-zone.
194 * <p>
195 * This will query the {@link Clock#system(ZoneId) system clock} to obtain the current year-month.
196 * Specifying the time-zone avoids dependence on the default time-zone.
197 * <p>
198 * Using this method will prevent the ability to use an alternate clock for testing
199 * because the clock is hard-coded.
200 *
201 * @param zone the zone ID to use, not null
202 * @return the current year-month using the system clock, not null
203 */
204 public static YearMonth now(ZoneId zone) {
205 return now(Clock.system(zone));
206 }
207
208 /**
209 * Obtains the current year-month from the specified clock.
210 * <p>
211 * This will query the specified clock to obtain the current year-month.
212 * Using this method allows the use of an alternate clock for testing.
213 * The alternate clock may be introduced using {@link Clock dependency injection}.
214 *
215 * @param clock the clock to use, not null
216 * @return the current year-month, not null
217 */
218 public static YearMonth now(Clock clock) {
219 final LocalDate now = LocalDate.now(clock); // called once
220 return YearMonth.of(now.getYear(), now.getMonth());
221 }
222
223 //-----------------------------------------------------------------------
224 /**
225 * Obtains an instance of {@code YearMonth} from a year and month.
226 *
227 * @param year the year to represent, from MIN_YEAR to MAX_YEAR
228 * @param month the month-of-year to represent, not null
229 * @return the year-month, not null
230 * @throws DateTimeException if the year value is invalid
231 */
232 public static YearMonth of(int year, Month month) {
233 Objects.requireNonNull(month, "month");
234 return of(year, month.getValue());
235 }
236
237 /**
238 * Obtains an instance of {@code YearMonth} from a year and month.
239 *
240 * @param year the year to represent, from MIN_YEAR to MAX_YEAR
241 * @param month the month-of-year to represent, from 1 (January) to 12 (December)
242 * @return the year-month, not null
243 * @throws DateTimeException if either field value is invalid
244 */
245 public static YearMonth of(int year, int month) {
246 YEAR.checkValidValue(year);
247 MONTH_OF_YEAR.checkValidValue(month);
248 return new YearMonth(year, month);
249 }
250
251 //-----------------------------------------------------------------------
252 /**
253 * Obtains an instance of {@code YearMonth} from a temporal object.
254 * <p>
255 * This obtains a year-month based on the specified temporal.
256 * A {@code TemporalAccessor} represents an arbitrary set of date and time information,
257 * which this factory converts to an instance of {@code YearMonth}.
258 * <p>
259 * The conversion extracts the {@link ChronoField#YEAR YEAR} and
260 * {@link ChronoField#MONTH_OF_YEAR MONTH_OF_YEAR} fields.
261 * The extraction is only permitted if the temporal object has an ISO
262 * chronology, or can be converted to a {@code LocalDate}.
263 * <p>
264 * This method matches the signature of the functional interface {@link TemporalQuery}
265 * allowing it to be used as a query via method reference, {@code YearMonth::from}.
266 *
267 * @param temporal the temporal object to convert, not null
268 * @return the year-month, not null
269 * @throws DateTimeException if unable to convert to a {@code YearMonth}
270 */
271 public static YearMonth from(TemporalAccessor temporal) {
272 if (temporal instanceof YearMonth) {
273 return (YearMonth) temporal;
274 }
275 Objects.requireNonNull(temporal, "temporal");
276 try {
277 if (IsoChronology.INSTANCE.equals(Chronology.from(temporal)) == false) {
278 temporal = LocalDate.from(temporal);
279 }
280 return of(temporal.get(YEAR), temporal.get(MONTH_OF_YEAR));
281 } catch (DateTimeException ex) {
282 throw new DateTimeException("Unable to obtain YearMonth from TemporalAccessor: " +
283 temporal + " of type " + temporal.getClass().getName(), ex);
284 }
285 }
286
287 //-----------------------------------------------------------------------
288 /**
289 * Obtains an instance of {@code YearMonth} from a text string such as {@code 2007-12}.
290 * <p>
291 * The string must represent a valid year-month.
292 * The format must be {@code uuuu-MM}.
293 * Years outside the range 0000 to 9999 must be prefixed by the plus or minus symbol.
294 *
295 * @param text the text to parse such as "2007-12", not null
296 * @return the parsed year-month, not null
297 * @throws DateTimeParseException if the text cannot be parsed
298 */
299 public static YearMonth parse(CharSequence text) {
300 return parse(text, PARSER);
301 }
302
303 /**
304 * Obtains an instance of {@code YearMonth} from a text string using a specific formatter.
305 * <p>
306 * The text is parsed using the formatter, returning a year-month.
307 *
308 * @param text the text to parse, not null
309 * @param formatter the formatter to use, not null
310 * @return the parsed year-month, not null
311 * @throws DateTimeParseException if the text cannot be parsed
312 */
313 public static YearMonth parse(CharSequence text, DateTimeFormatter formatter) {
314 Objects.requireNonNull(formatter, "formatter");
315 return formatter.parse(text, YearMonth::from);
316 }
317
318 //-----------------------------------------------------------------------
319 /**
320 * Constructor.
321 *
322 * @param year the year to represent, validated from MIN_YEAR to MAX_YEAR
323 * @param month the month-of-year to represent, validated from 1 (January) to 12 (December)
324 */
325 private YearMonth(int year, int month) {
326 this.year = year;
327 this.month = (byte) month;
328 }
329
330 /**
331 * Returns a copy of this year-month with the new year and month, checking
332 * to see if a new object is in fact required.
333 *
334 * @param newYear the year to represent, validated from MIN_YEAR to MAX_YEAR
335 * @param newMonth the month-of-year to represent, validated not null
336 * @return the year-month, not null
337 */
338 private YearMonth with(int newYear, int newMonth) {
339 if (year == newYear && month == newMonth) {
340 return this;
341 }
342 return new YearMonth(newYear, newMonth);
343 }
344
345 //-----------------------------------------------------------------------
346 /**
347 * Checks if the specified field is supported.
348 * <p>
349 * This checks if this year-month can be queried for the specified field.
350 * If false, then calling the {@link #range(TemporalField) range},
351 * {@link #get(TemporalField) get} and {@link #with(TemporalField, long)}
352 * methods will throw an exception.
353 * <p>
354 * If the field is a {@link ChronoField} then the query is implemented here.
355 * The supported fields are:
356 * <ul>
357 * <li>{@code MONTH_OF_YEAR}
358 * <li>{@code PROLEPTIC_MONTH}
359 * <li>{@code YEAR_OF_ERA}
360 * <li>{@code YEAR}
361 * <li>{@code ERA}
362 * </ul>
363 * All other {@code ChronoField} instances will return false.
364 * <p>
365 * If the field is not a {@code ChronoField}, then the result of this method
366 * is obtained by invoking {@code TemporalField.isSupportedBy(TemporalAccessor)}
367 * passing {@code this} as the argument.
368 * Whether the field is supported is determined by the field.
369 *
370 * @param field the field to check, null returns false
371 * @return true if the field is supported on this year-month, false if not
372 */
373 @Override
374 public boolean isSupported(TemporalField field) {
375 if (field instanceof ChronoField) {
376 return field == YEAR || field == MONTH_OF_YEAR ||
377 field == PROLEPTIC_MONTH || field == YEAR_OF_ERA || field == ERA;
378 }
379 return field != null && field.isSupportedBy(this);
380 }
381
382 /**
383 * Checks if the specified unit is supported.
384 * <p>
385 * This checks if the specified unit can be added to, or subtracted from, this year-month.
386 * If false, then calling the {@link #plus(long, TemporalUnit)} and
387 * {@link #minus(long, TemporalUnit) minus} methods will throw an exception.
388 * <p>
389 * If the unit is a {@link ChronoUnit} then the query is implemented here.
390 * The supported units are:
391 * <ul>
392 * <li>{@code MONTHS}
393 * <li>{@code YEARS}
394 * <li>{@code DECADES}
395 * <li>{@code CENTURIES}
396 * <li>{@code MILLENNIA}
397 * <li>{@code ERAS}
398 * </ul>
399 * All other {@code ChronoUnit} instances will return false.
400 * <p>
401 * If the unit is not a {@code ChronoUnit}, then the result of this method
402 * is obtained by invoking {@code TemporalUnit.isSupportedBy(Temporal)}
403 * passing {@code this} as the argument.
404 * Whether the unit is supported is determined by the unit.
405 *
406 * @param unit the unit to check, null returns false
407 * @return true if the unit can be added/subtracted, false if not
408 */
409 @Override
410 public boolean isSupported(TemporalUnit unit) {
411 if (unit instanceof ChronoUnit) {
412 return unit == MONTHS || unit == YEARS || unit == DECADES || unit == CENTURIES || unit == MILLENNIA || unit == ERAS;
413 }
414 return unit != null && unit.isSupportedBy(this);
415 }
416
417 //-----------------------------------------------------------------------
418 /**
419 * Gets the range of valid values for the specified field.
420 * <p>
421 * The range object expresses the minimum and maximum valid values for a field.
422 * This year-month is used to enhance the accuracy of the returned range.
423 * If it is not possible to return the range, because the field is not supported
424 * or for some other reason, an exception is thrown.
425 * <p>
426 * If the field is a {@link ChronoField} then the query is implemented here.
427 * The {@link #isSupported(TemporalField) supported fields} will return
428 * appropriate range instances.
429 * All other {@code ChronoField} instances will throw an {@code UnsupportedTemporalTypeException}.
430 * <p>
431 * If the field is not a {@code ChronoField}, then the result of this method
432 * is obtained by invoking {@code TemporalField.rangeRefinedBy(TemporalAccessor)}
433 * passing {@code this} as the argument.
434 * Whether the range can be obtained is determined by the field.
435 *
436 * @param field the field to query the range for, not null
437 * @return the range of valid values for the field, not null
438 * @throws DateTimeException if the range for the field cannot be obtained
439 * @throws UnsupportedTemporalTypeException if the field is not supported
440 */
441 @Override
442 public ValueRange range(TemporalField field) {
443 if (field == YEAR_OF_ERA) {
444 return (getYear() <= 0 ? ValueRange.of(1, Year.MAX_VALUE + 1) : ValueRange.of(1, Year.MAX_VALUE));
445 }
446 return Temporal.super.range(field);
447 }
448
449 /**
450 * Gets the value of the specified field from this year-month as an {@code int}.
451 * <p>
452 * This queries this year-month for the value of the specified field.
453 * The returned value will always be within the valid range of values for the field.
454 * If it is not possible to return the value, because the field is not supported
455 * or for some other reason, an exception is thrown.
456 * <p>
457 * If the field is a {@link ChronoField} then the query is implemented here.
458 * The {@link #isSupported(TemporalField) supported fields} will return valid
459 * values based on this year-month, except {@code PROLEPTIC_MONTH} which is too
460 * large to fit in an {@code int} and throw a {@code DateTimeException}.
461 * All other {@code ChronoField} instances will throw an {@code UnsupportedTemporalTypeException}.
462 * <p>
463 * If the field is not a {@code ChronoField}, then the result of this method
464 * is obtained by invoking {@code TemporalField.getFrom(TemporalAccessor)}
465 * passing {@code this} as the argument. Whether the value can be obtained,
466 * and what the value represents, is determined by the field.
467 *
468 * @param field the field to get, not null
469 * @return the value for the field
470 * @throws DateTimeException if a value for the field cannot be obtained or
471 * the value is outside the range of valid values for the field
472 * @throws UnsupportedTemporalTypeException if the field is not supported or
473 * the range of values exceeds an {@code int}
474 * @throws ArithmeticException if numeric overflow occurs
475 */
476 @Override // override for Javadoc
477 public int get(TemporalField field) {
478 return range(field).checkValidIntValue(getLong(field), field);
479 }
480
481 /**
482 * Gets the value of the specified field from this year-month as a {@code long}.
483 * <p>
484 * This queries this year-month for the value of the specified field.
485 * If it is not possible to return the value, because the field is not supported
486 * or for some other reason, an exception is thrown.
487 * <p>
488 * If the field is a {@link ChronoField} then the query is implemented here.
489 * The {@link #isSupported(TemporalField) supported fields} will return valid
490 * values based on this year-month.
491 * All other {@code ChronoField} instances will throw an {@code UnsupportedTemporalTypeException}.
492 * <p>
493 * If the field is not a {@code ChronoField}, then the result of this method
494 * is obtained by invoking {@code TemporalField.getFrom(TemporalAccessor)}
495 * passing {@code this} as the argument. Whether the value can be obtained,
496 * and what the value represents, is determined by the field.
497 *
498 * @param field the field to get, not null
499 * @return the value for the field
500 * @throws DateTimeException if a value for the field cannot be obtained
501 * @throws UnsupportedTemporalTypeException if the field is not supported
502 * @throws ArithmeticException if numeric overflow occurs
503 */
504 @Override
505 public long getLong(TemporalField field) {
506 if (field instanceof ChronoField chronoField) {
507 return switch (chronoField) {
508 case MONTH_OF_YEAR -> month;
509 case PROLEPTIC_MONTH -> getProlepticMonth();
510 case YEAR_OF_ERA -> (year < 1 ? 1 - year : year);
511 case YEAR -> year;
512 case ERA -> (year < 1 ? 0 : 1);
513 default -> throw new UnsupportedTemporalTypeException("Unsupported field: " + field);
514 };
515 }
516 return field.getFrom(this);
517 }
518
519 private long getProlepticMonth() {
520 return (year * 12L + month - 1);
521 }
522
523 //-----------------------------------------------------------------------
524 /**
525 * Gets the year field.
526 * <p>
527 * This method returns the primitive {@code int} value for the year.
528 * <p>
529 * The year returned by this method is proleptic as per {@code get(YEAR)}.
530 *
531 * @return the year, from MIN_YEAR to MAX_YEAR
532 */
533 public int getYear() {
534 return year;
535 }
536
537 /**
538 * Gets the month-of-year field from 1 to 12.
539 * <p>
540 * This method returns the month as an {@code int} from 1 to 12.
541 * Application code is frequently clearer if the enum {@link Month}
542 * is used by calling {@link #getMonth()}.
543 *
544 * @return the month-of-year, from 1 to 12
545 * @see #getMonth()
546 */
547 public int getMonthValue() {
548 return month;
549 }
550
551 /**
552 * Gets the month-of-year field using the {@code Month} enum.
553 * <p>
554 * This method returns the enum {@link Month} for the month.
555 * This avoids confusion as to what {@code int} values mean.
556 * If you need access to the primitive {@code int} value then the enum
557 * provides the {@link Month#getValue() int value}.
558 *
559 * @return the month-of-year, not null
560 * @see #getMonthValue()
561 */
562 public Month getMonth() {
563 return Month.of(month);
564 }
565
566 //-----------------------------------------------------------------------
567 /**
568 * Checks if the year is a leap year, according to the ISO proleptic
569 * calendar system rules.
570 * <p>
571 * This method applies the current rules for leap years across the whole time-line.
572 * In general, a year is a leap year if it is divisible by four without
573 * remainder. However, years divisible by 100, are not leap years, with
574 * the exception of years divisible by 400 which are.
575 * <p>
576 * For example, 1904 is a leap year it is divisible by 4.
577 * 1900 was not a leap year as it is divisible by 100, however 2000 was a
578 * leap year as it is divisible by 400.
579 * <p>
580 * The calculation is proleptic - applying the same rules into the far future and far past.
581 * This is historically inaccurate, but is correct for the ISO-8601 standard.
582 *
583 * @return true if the year is leap, false otherwise
584 */
585 public boolean isLeapYear() {
586 return IsoChronology.INSTANCE.isLeapYear(year);
587 }
588
589 /**
590 * Checks if the day-of-month is valid for this year-month.
591 * <p>
592 * This method checks whether this year and month and the input day form
593 * a valid date.
594 *
595 * @param dayOfMonth the day-of-month to validate, from 1 to 31, invalid value returns false
596 * @return true if the day is valid for this year-month
597 */
598 public boolean isValidDay(int dayOfMonth) {
599 return dayOfMonth >= 1 && dayOfMonth <= lengthOfMonth();
600 }
601
602 /**
603 * Returns the length of the month, taking account of the year.
604 * <p>
605 * This returns the length of the month in days.
606 * For example, a date in January would return 31.
607 *
608 * @return the length of the month in days, from 28 to 31
609 */
610 public int lengthOfMonth() {
611 return getMonth().length(isLeapYear());
612 }
613
614 /**
615 * Returns the length of the year.
616 * <p>
617 * This returns the length of the year in days, either 365 or 366.
618 *
619 * @return 366 if the year is leap, 365 otherwise
620 */
621 public int lengthOfYear() {
622 return (isLeapYear() ? 366 : 365);
623 }
624
625 //-----------------------------------------------------------------------
626 /**
627 * Returns an adjusted copy of this year-month.
628 * <p>
629 * This returns a {@code YearMonth}, based on this one, with the year-month adjusted.
630 * The adjustment takes place using the specified adjuster strategy object.
631 * Read the documentation of the adjuster to understand what adjustment will be made.
632 * <p>
633 * A simple adjuster might simply set the one of the fields, such as the year field.
634 * A more complex adjuster might set the year-month to the next month that
635 * Halley's comet will pass the Earth.
636 * <p>
637 * The result of this method is obtained by invoking the
638 * {@link TemporalAdjuster#adjustInto(Temporal)} method on the
639 * specified adjuster passing {@code this} as the argument.
640 * <p>
641 * This instance is immutable and unaffected by this method call.
642 *
643 * @param adjuster the adjuster to use, not null
644 * @return a {@code YearMonth} based on {@code this} with the adjustment made, not null
645 * @throws DateTimeException if the adjustment cannot be made
646 * @throws ArithmeticException if numeric overflow occurs
647 */
648 @Override
649 public YearMonth with(TemporalAdjuster adjuster) {
650 return (YearMonth) adjuster.adjustInto(this);
651 }
652
653 /**
654 * Returns a copy of this year-month with the specified field set to a new value.
655 * <p>
656 * This returns a {@code YearMonth}, based on this one, with the value
657 * for the specified field changed.
658 * This can be used to change any supported field, such as the year or month.
659 * If it is not possible to set the value, because the field is not supported or for
660 * some other reason, an exception is thrown.
661 * <p>
662 * If the field is a {@link ChronoField} then the adjustment is implemented here.
663 * The supported fields behave as follows:
664 * <ul>
665 * <li>{@code MONTH_OF_YEAR} -
666 * Returns a {@code YearMonth} with the specified month-of-year.
667 * The year will be unchanged.
668 * <li>{@code PROLEPTIC_MONTH} -
669 * Returns a {@code YearMonth} with the specified proleptic-month.
670 * This completely replaces the year and month of this object.
671 * <li>{@code YEAR_OF_ERA} -
672 * Returns a {@code YearMonth} with the specified year-of-era
673 * The month and era will be unchanged.
674 * <li>{@code YEAR} -
675 * Returns a {@code YearMonth} with the specified year.
676 * The month will be unchanged.
677 * <li>{@code ERA} -
678 * Returns a {@code YearMonth} with the specified era.
679 * The month and year-of-era will be unchanged.
680 * </ul>
681 * <p>
682 * In all cases, if the new value is outside the valid range of values for the field
683 * then a {@code DateTimeException} will be thrown.
684 * <p>
685 * All other {@code ChronoField} instances will throw an {@code UnsupportedTemporalTypeException}.
686 * <p>
687 * If the field is not a {@code ChronoField}, then the result of this method
688 * is obtained by invoking {@code TemporalField.adjustInto(Temporal, long)}
689 * passing {@code this} as the argument. In this case, the field determines
690 * whether and how to adjust the instant.
691 * <p>
692 * This instance is immutable and unaffected by this method call.
693 *
694 * @param field the field to set in the result, not null
695 * @param newValue the new value of the field in the result
696 * @return a {@code YearMonth} based on {@code this} with the specified field set, not null
697 * @throws DateTimeException if the field cannot be set
698 * @throws UnsupportedTemporalTypeException if the field is not supported
699 * @throws ArithmeticException if numeric overflow occurs
700 */
701 @Override
702 public YearMonth with(TemporalField field, long newValue) {
703 if (field instanceof ChronoField chronoField) {
704 chronoField.checkValidValue(newValue);
705 return switch (chronoField) {
706 case MONTH_OF_YEAR -> withMonth((int) newValue);
707 case PROLEPTIC_MONTH -> plusMonths(newValue - getProlepticMonth());
708 case YEAR_OF_ERA -> withYear((int) (year < 1 ? 1 - newValue : newValue));
709 case YEAR -> withYear((int) newValue);
710 case ERA -> (getLong(ERA) == newValue ? this : withYear(1 - year));
711 default -> throw new UnsupportedTemporalTypeException("Unsupported field: " + field);
712 };
713 }
714 return field.adjustInto(this, newValue);
715 }
716
717 //-----------------------------------------------------------------------
718 /**
719 * Returns a copy of this {@code YearMonth} with the year altered.
720 * <p>
721 * This instance is immutable and unaffected by this method call.
722 *
723 * @param year the year to set in the returned year-month, from MIN_YEAR to MAX_YEAR
724 * @return a {@code YearMonth} based on this year-month with the requested year, not null
725 * @throws DateTimeException if the year value is invalid
726 */
727 public YearMonth withYear(int year) {
728 YEAR.checkValidValue(year);
729 return with(year, month);
730 }
731
732 /**
733 * Returns a copy of this {@code YearMonth} with the month-of-year altered.
734 * <p>
735 * This instance is immutable and unaffected by this method call.
736 *
737 * @param month the month-of-year to set in the returned year-month, from 1 (January) to 12 (December)
738 * @return a {@code YearMonth} based on this year-month with the requested month, not null
739 * @throws DateTimeException if the month-of-year value is invalid
740 */
741 public YearMonth withMonth(int month) {
742 MONTH_OF_YEAR.checkValidValue(month);
743 return with(year, month);
744 }
745
746 //-----------------------------------------------------------------------
747 /**
748 * Returns a copy of this year-month with the specified amount added.
749 * <p>
750 * This returns a {@code YearMonth}, based on this one, with the specified amount added.
751 * The amount is typically {@link Period} but may be any other type implementing
752 * the {@link TemporalAmount} interface.
753 * <p>
754 * The calculation is delegated to the amount object by calling
755 * {@link TemporalAmount#addTo(Temporal)}. The amount implementation is free
756 * to implement the addition in any way it wishes, however it typically
757 * calls back to {@link #plus(long, TemporalUnit)}. Consult the documentation
758 * of the amount implementation to determine if it can be successfully added.
759 * <p>
760 * This instance is immutable and unaffected by this method call.
761 *
762 * @param amountToAdd the amount to add, not null
763 * @return a {@code YearMonth} based on this year-month with the addition made, not null
764 * @throws DateTimeException if the addition cannot be made
765 * @throws ArithmeticException if numeric overflow occurs
766 */
767 @Override
768 public YearMonth plus(TemporalAmount amountToAdd) {
769 return (YearMonth) amountToAdd.addTo(this);
770 }
771
772 /**
773 * Returns a copy of this year-month with the specified amount added.
774 * <p>
775 * This returns a {@code YearMonth}, based on this one, with the amount
776 * in terms of the unit added. If it is not possible to add the amount, because the
777 * unit is not supported or for some other reason, an exception is thrown.
778 * <p>
779 * If the field is a {@link ChronoUnit} then the addition is implemented here.
780 * The supported fields behave as follows:
781 * <ul>
782 * <li>{@code MONTHS} -
783 * Returns a {@code YearMonth} with the specified number of months added.
784 * This is equivalent to {@link #plusMonths(long)}.
785 * <li>{@code YEARS} -
786 * Returns a {@code YearMonth} with the specified number of years added.
787 * This is equivalent to {@link #plusYears(long)}.
788 * <li>{@code DECADES} -
789 * Returns a {@code YearMonth} with the specified number of decades added.
790 * This is equivalent to calling {@link #plusYears(long)} with the amount
791 * multiplied by 10.
792 * <li>{@code CENTURIES} -
793 * Returns a {@code YearMonth} with the specified number of centuries added.
794 * This is equivalent to calling {@link #plusYears(long)} with the amount
795 * multiplied by 100.
796 * <li>{@code MILLENNIA} -
797 * Returns a {@code YearMonth} with the specified number of millennia added.
798 * This is equivalent to calling {@link #plusYears(long)} with the amount
799 * multiplied by 1,000.
800 * <li>{@code ERAS} -
801 * Returns a {@code YearMonth} with the specified number of eras added.
802 * Only two eras are supported so the amount must be one, zero or minus one.
803 * If the amount is non-zero then the year is changed such that the year-of-era
804 * is unchanged.
805 * </ul>
806 * <p>
807 * All other {@code ChronoUnit} instances will throw an {@code UnsupportedTemporalTypeException}.
808 * <p>
809 * If the field is not a {@code ChronoUnit}, then the result of this method
810 * is obtained by invoking {@code TemporalUnit.addTo(Temporal, long)}
811 * passing {@code this} as the argument. In this case, the unit determines
812 * whether and how to perform the addition.
813 * <p>
814 * This instance is immutable and unaffected by this method call.
815 *
816 * @param amountToAdd the amount of the unit to add to the result, may be negative
817 * @param unit the unit of the amount to add, not null
818 * @return a {@code YearMonth} based on this year-month with the specified amount added, not null
819 * @throws DateTimeException if the addition cannot be made
820 * @throws UnsupportedTemporalTypeException if the unit is not supported
821 * @throws ArithmeticException if numeric overflow occurs
822 */
823 @Override
824 public YearMonth plus(long amountToAdd, TemporalUnit unit) {
825 if (unit instanceof ChronoUnit chronoUnit) {
826 return switch (chronoUnit) {
827 case MONTHS -> plusMonths(amountToAdd);
828 case YEARS -> plusYears(amountToAdd);
829 case DECADES -> plusYears(Math.multiplyExact(amountToAdd, 10));
830 case CENTURIES -> plusYears(Math.multiplyExact(amountToAdd, 100));
831 case MILLENNIA -> plusYears(Math.multiplyExact(amountToAdd, 1000));
832 case ERAS -> with(ERA, Math.addExact(getLong(ERA), amountToAdd));
833 default -> throw new UnsupportedTemporalTypeException("Unsupported unit: " + unit);
834 };
835 }
836 return unit.addTo(this, amountToAdd);
837 }
838
839 /**
840 * Returns a copy of this {@code YearMonth} with the specified number of years added.
841 * <p>
842 * This instance is immutable and unaffected by this method call.
843 *
844 * @param yearsToAdd the years to add, may be negative
845 * @return a {@code YearMonth} based on this year-month with the years added, not null
846 * @throws DateTimeException if the result exceeds the supported range
847 */
848 public YearMonth plusYears(long yearsToAdd) {
849 if (yearsToAdd == 0) {
850 return this;
851 }
852 int newYear = YEAR.checkValidIntValue(year + yearsToAdd); // safe overflow
853 return with(newYear, month);
854 }
855
856 /**
857 * Returns a copy of this {@code YearMonth} with the specified number of months added.
858 * <p>
859 * This instance is immutable and unaffected by this method call.
860 *
861 * @param monthsToAdd the months to add, may be negative
862 * @return a {@code YearMonth} based on this year-month with the months added, not null
863 * @throws DateTimeException if the result exceeds the supported range
864 */
865 public YearMonth plusMonths(long monthsToAdd) {
866 if (monthsToAdd == 0) {
867 return this;
868 }
869 long monthCount = year * 12L + (month - 1);
870 long calcMonths = monthCount + monthsToAdd; // safe overflow
871 int newYear = YEAR.checkValidIntValue(Math.floorDiv(calcMonths, 12));
872 int newMonth = Math.floorMod(calcMonths, 12) + 1;
873 return with(newYear, newMonth);
874 }
875
876 //-----------------------------------------------------------------------
877 /**
878 * Returns a copy of this year-month with the specified amount subtracted.
879 * <p>
880 * This returns a {@code YearMonth}, based on this one, with the specified amount subtracted.
881 * The amount is typically {@link Period} but may be any other type implementing
882 * the {@link TemporalAmount} interface.
883 * <p>
884 * The calculation is delegated to the amount object by calling
885 * {@link TemporalAmount#subtractFrom(Temporal)}. The amount implementation is free
886 * to implement the subtraction in any way it wishes, however it typically
887 * calls back to {@link #minus(long, TemporalUnit)}. Consult the documentation
888 * of the amount implementation to determine if it can be successfully subtracted.
889 * <p>
890 * This instance is immutable and unaffected by this method call.
891 *
892 * @param amountToSubtract the amount to subtract, not null
893 * @return a {@code YearMonth} based on this year-month with the subtraction made, not null
894 * @throws DateTimeException if the subtraction cannot be made
895 * @throws ArithmeticException if numeric overflow occurs
896 */
897 @Override
898 public YearMonth minus(TemporalAmount amountToSubtract) {
899 return (YearMonth) amountToSubtract.subtractFrom(this);
900 }
901
902 /**
903 * Returns a copy of this year-month with the specified amount subtracted.
904 * <p>
905 * This returns a {@code YearMonth}, based on this one, with the amount
906 * in terms of the unit subtracted. If it is not possible to subtract the amount,
907 * because the unit is not supported or for some other reason, an exception is thrown.
908 * <p>
909 * This method is equivalent to {@link #plus(long, TemporalUnit)} with the amount negated.
910 * See that method for a full description of how addition, and thus subtraction, works.
911 * <p>
912 * This instance is immutable and unaffected by this method call.
913 *
914 * @param amountToSubtract the amount of the unit to subtract from the result, may be negative
915 * @param unit the unit of the amount to subtract, not null
916 * @return a {@code YearMonth} based on this year-month with the specified amount subtracted, not null
917 * @throws DateTimeException if the subtraction cannot be made
918 * @throws UnsupportedTemporalTypeException if the unit is not supported
919 * @throws ArithmeticException if numeric overflow occurs
920 */
921 @Override
922 public YearMonth minus(long amountToSubtract, TemporalUnit unit) {
923 return (amountToSubtract == Long.MIN_VALUE ? plus(Long.MAX_VALUE, unit).plus(1, unit) : plus(-amountToSubtract, unit));
924 }
925
926 /**
927 * Returns a copy of this {@code YearMonth} with the specified number of years subtracted.
928 * <p>
929 * This instance is immutable and unaffected by this method call.
930 *
931 * @param yearsToSubtract the years to subtract, may be negative
932 * @return a {@code YearMonth} based on this year-month with the years subtracted, not null
933 * @throws DateTimeException if the result exceeds the supported range
934 */
935 public YearMonth minusYears(long yearsToSubtract) {
936 return (yearsToSubtract == Long.MIN_VALUE ? plusYears(Long.MAX_VALUE).plusYears(1) : plusYears(-yearsToSubtract));
937 }
938
939 /**
940 * Returns a copy of this {@code YearMonth} with the specified number of months subtracted.
941 * <p>
942 * This instance is immutable and unaffected by this method call.
943 *
944 * @param monthsToSubtract the months to subtract, may be negative
945 * @return a {@code YearMonth} based on this year-month with the months subtracted, not null
946 * @throws DateTimeException if the result exceeds the supported range
947 */
948 public YearMonth minusMonths(long monthsToSubtract) {
949 return (monthsToSubtract == Long.MIN_VALUE ? plusMonths(Long.MAX_VALUE).plusMonths(1) : plusMonths(-monthsToSubtract));
950 }
951
952 //-----------------------------------------------------------------------
953 /**
954 * Queries this year-month using the specified query.
955 * <p>
956 * This queries this year-month using the specified query strategy object.
957 * The {@code TemporalQuery} object defines the logic to be used to
958 * obtain the result. Read the documentation of the query to understand
959 * what the result of this method will be.
960 * <p>
961 * The result of this method is obtained by invoking the
962 * {@link TemporalQuery#queryFrom(TemporalAccessor)} method on the
963 * specified query passing {@code this} as the argument.
964 *
965 * @param <R> the type of the result
966 * @param query the query to invoke, not null
967 * @return the query result, null may be returned (defined by the query)
968 * @throws DateTimeException if unable to query (defined by the query)
969 * @throws ArithmeticException if numeric overflow occurs (defined by the query)
970 */
971 @SuppressWarnings("unchecked")
972 @Override
973 public <R> R query(TemporalQuery<R> query) {
974 if (query == TemporalQueries.chronology()) {
975 return (R) IsoChronology.INSTANCE;
976 } else if (query == TemporalQueries.precision()) {
977 return (R) MONTHS;
978 }
979 return Temporal.super.query(query);
980 }
981
982 /**
983 * Adjusts the specified temporal object to have this year-month.
984 * <p>
985 * This returns a temporal object of the same observable type as the input
986 * with the year and month changed to be the same as this.
987 * <p>
988 * The adjustment is equivalent to using {@link Temporal#with(TemporalField, long)}
989 * passing {@link ChronoField#PROLEPTIC_MONTH} as the field.
990 * If the specified temporal object does not use the ISO calendar system then
991 * a {@code DateTimeException} is thrown.
992 * <p>
993 * In most cases, it is clearer to reverse the calling pattern by using
994 * {@link Temporal#with(TemporalAdjuster)}:
995 * <pre>
996 * // these two lines are equivalent, but the second approach is recommended
997 * temporal = thisYearMonth.adjustInto(temporal);
998 * temporal = temporal.with(thisYearMonth);
999 * </pre>
1000 * <p>
1001 * This instance is immutable and unaffected by this method call.
1002 *
1003 * @param temporal the target object to be adjusted, not null
1004 * @return the adjusted object, not null
1005 * @throws DateTimeException if unable to make the adjustment
1006 * @throws ArithmeticException if numeric overflow occurs
1007 */
1008 @Override
1009 public Temporal adjustInto(Temporal temporal) {
1010 if (Chronology.from(temporal).equals(IsoChronology.INSTANCE) == false) {
1011 throw new DateTimeException("Adjustment only supported on ISO date-time");
1012 }
1013 return temporal.with(PROLEPTIC_MONTH, getProlepticMonth());
1014 }
1015
1016 /**
1017 * Calculates the amount of time until another year-month in terms of the specified unit.
1018 * <p>
1019 * This calculates the amount of time between two {@code YearMonth}
1020 * objects in terms of a single {@code TemporalUnit}.
1021 * The start and end points are {@code this} and the specified year-month.
1022 * The result will be negative if the end is before the start.
1023 * The {@code Temporal} passed to this method is converted to a
1024 * {@code YearMonth} using {@link #from(TemporalAccessor)}.
1025 * For example, the amount in years between two year-months can be calculated
1026 * using {@code startYearMonth.until(endYearMonth, YEARS)}.
1027 * <p>
1028 * The calculation returns a whole number, representing the number of
1029 * complete units between the two year-months.
1030 * For example, the amount in decades between 2012-06 and 2032-05
1031 * will only be one decade as it is one month short of two decades.
1032 * <p>
1033 * There are two equivalent ways of using this method.
1034 * The first is to invoke this method.
1035 * The second is to use {@link TemporalUnit#between(Temporal, Temporal)}:
1036 * <pre>
1037 * // these two lines are equivalent
1038 * amount = start.until(end, MONTHS);
1039 * amount = MONTHS.between(start, end);
1040 * </pre>
1041 * The choice should be made based on which makes the code more readable.
1042 * <p>
1043 * The calculation is implemented in this method for {@link ChronoUnit}.
1044 * The units {@code MONTHS}, {@code YEARS}, {@code DECADES},
1045 * {@code CENTURIES}, {@code MILLENNIA} and {@code ERAS} are supported.
1046 * Other {@code ChronoUnit} values will throw an exception.
1047 * <p>
1048 * If the unit is not a {@code ChronoUnit}, then the result of this method
1049 * is obtained by invoking {@code TemporalUnit.between(Temporal, Temporal)}
1050 * passing {@code this} as the first argument and the converted input temporal
1051 * as the second argument.
1052 * <p>
1053 * This instance is immutable and unaffected by this method call.
1054 *
1055 * @param endExclusive the end date, exclusive, which is converted to a {@code YearMonth}, not null
1056 * @param unit the unit to measure the amount in, not null
1057 * @return the amount of time between this year-month and the end year-month
1058 * @throws DateTimeException if the amount cannot be calculated, or the end
1059 * temporal cannot be converted to a {@code YearMonth}
1060 * @throws UnsupportedTemporalTypeException if the unit is not supported
1061 * @throws ArithmeticException if numeric overflow occurs
1062 */
1063 @Override
1064 public long until(Temporal endExclusive, TemporalUnit unit) {
1065 YearMonth end = YearMonth.from(endExclusive);
1066 if (unit instanceof ChronoUnit chronoUnit) {
1067 long monthsUntil = end.getProlepticMonth() - getProlepticMonth(); // no overflow
1068 return switch (chronoUnit) {
1069 case MONTHS -> monthsUntil;
1070 case YEARS -> monthsUntil / 12;
1071 case DECADES -> monthsUntil / 120;
1072 case CENTURIES -> monthsUntil / 1200;
1073 case MILLENNIA -> monthsUntil / 12000;
1074 case ERAS -> end.getLong(ERA) - getLong(ERA);
1075 default -> throw new UnsupportedTemporalTypeException("Unsupported unit: " + unit);
1076 };
1077 }
1078 return unit.between(this, end);
1079 }
1080
1081 /**
1082 * Formats this year-month using the specified formatter.
1083 * <p>
1084 * This year-month will be passed to the formatter to produce a string.
1085 *
1086 * @param formatter the formatter to use, not null
1087 * @return the formatted year-month string, not null
1088 * @throws DateTimeException if an error occurs during printing
1089 */
1090 public String format(DateTimeFormatter formatter) {
1091 Objects.requireNonNull(formatter, "formatter");
1092 return formatter.format(this);
1093 }
1094
1095 //-----------------------------------------------------------------------
1096 /**
1097 * Combines this year-month with a day-of-month to create a {@code LocalDate}.
1098 * <p>
1099 * This returns a {@code LocalDate} formed from this year-month and the specified day-of-month.
1100 * <p>
1101 * The day-of-month value must be valid for the year-month.
1102 * <p>
1103 * This method can be used as part of a chain to produce a date:
1104 * <pre>
1105 * LocalDate date = year.atMonth(month).atDay(day);
1106 * </pre>
1107 *
1108 * @param dayOfMonth the day-of-month to use, from 1 to 31
1109 * @return the date formed from this year-month and the specified day, not null
1110 * @throws DateTimeException if the day is invalid for the year-month
1111 * @see #isValidDay(int)
1112 */
1113 public LocalDate atDay(int dayOfMonth) {
1114 return LocalDate.of(year, month, dayOfMonth);
1115 }
1116
1117 /**
1118 * Returns a {@code LocalDate} at the end of the month.
1119 * <p>
1120 * This returns a {@code LocalDate} based on this year-month.
1121 * The day-of-month is set to the last valid day of the month, taking
1122 * into account leap years.
1123 * <p>
1124 * This method can be used as part of a chain to produce a date:
1125 * <pre>
1126 * LocalDate date = year.atMonth(month).atEndOfMonth();
1127 * </pre>
1128 *
1129 * @return the last valid date of this year-month, not null
1130 */
1131 public LocalDate atEndOfMonth() {
1132 return LocalDate.of(year, month, lengthOfMonth());
1133 }
1134
1135 //-----------------------------------------------------------------------
1136 /**
1137 * Compares this year-month to another year-month.
1138 * <p>
1139 * The comparison is based first on the value of the year, then on the value of the month.
1140 * It is "consistent with equals", as defined by {@link Comparable}.
1141 *
1142 * @param other the other year-month to compare to, not null
1143 * @return the comparator value, that is less than zero if this is before {@code other},
1144 * zero if they are equal, greater than zero if this is after {@code other}
1145 * @see #isBefore
1146 * @see #isAfter
1147 */
1148 @Override
1149 public int compareTo(YearMonth other) {
1150 int cmp = (year - other.year);
1151 if (cmp == 0) {
1152 cmp = (month - other.month);
1153 }
1154 return cmp;
1155 }
1156
1157 /**
1158 * Checks if this year-month is after the specified year-month.
1159 *
1160 * @param other the other year-month to compare to, not null
1161 * @return true if this is after the specified year-month
1162 */
1163 public boolean isAfter(YearMonth other) {
1164 return compareTo(other) > 0;
1165 }
1166
1167 /**
1168 * Checks if this year-month is before the specified year-month.
1169 *
1170 * @param other the other year-month to compare to, not null
1171 * @return true if this point is before the specified year-month
1172 */
1173 public boolean isBefore(YearMonth other) {
1174 return compareTo(other) < 0;
1175 }
1176
1177 //-----------------------------------------------------------------------
1178 /**
1179 * Checks if this year-month is equal to another year-month.
1180 * <p>
1181 * The comparison is based on the time-line position of the year-months.
1182 *
1183 * @param obj the object to check, null returns false
1184 * @return true if this is equal to the other year-month
1185 */
1186 @Override
1187 public boolean equals(Object obj) {
1188 if (this == obj) {
1189 return true;
1190 }
1191 return (obj instanceof YearMonth other)
1192 && year == other.year
1193 && month == other.month;
1194 }
1195
1196 /**
1197 * A hash code for this year-month.
1198 *
1199 * @return a suitable hash code
1200 */
1201 @Override
1202 public int hashCode() {
1203 return year ^ (month << 27);
1204 }
1205
1206 //-----------------------------------------------------------------------
1207 /**
1208 * Outputs this year-month as a {@code String}, such as {@code 2007-12}.
1209 * <p>
1210 * The output will be in the format {@code uuuu-MM}:
1211 *
1212 * @return a string representation of this year-month, not null
1213 */
1214 @Override
1215 public String toString() {
1216 int absYear = Math.abs(year);
1217 StringBuilder buf = new StringBuilder(9);
1218 if (absYear < 10000) {
1219 if (year < 0) {
1220 buf.append('-');
1221 }
1222 DecimalDigits.appendQuad(buf, absYear);
1223 } else {
1224 buf.append(year);
1225 }
1226 buf.append('-');
1227 DecimalDigits.appendPair(buf, month);
1228 return buf.toString();
1229 }
1230
1231 //-----------------------------------------------------------------------
1232 /**
1233 * Writes the object using a
1234 * <a href="{@docRoot}/serialized-form.html#java.time.Ser">dedicated serialized form</a>.
1235 * @serialData
1236 * <pre>
1237 * out.writeByte(12); // identifies a YearMonth
1238 * out.writeInt(year);
1239 * out.writeByte(month);
1240 * </pre>
1241 *
1242 * @return the instance of {@code Ser}, not null
1243 */
1244 @java.io.Serial
1245 private Object writeReplace() {
1246 return new Ser(Ser.YEAR_MONTH_TYPE, this);
1247 }
1248
1249 /**
1250 * Defend against malicious streams.
1251 *
1252 * @param s the stream to read
1253 * @throws InvalidObjectException always
1254 */
1255 @java.io.Serial
1256 private void readObject(ObjectInputStream s) throws InvalidObjectException {
1257 throw new InvalidObjectException("Deserialization via serialization delegate");
1258 }
1259
1260 void writeExternal(DataOutput out) throws IOException {
1261 out.writeInt(year);
1262 out.writeByte(month);
1263 }
1264
1265 static YearMonth readExternal(DataInput in) throws IOException {
1266 int year = in.readInt();
1267 byte month = in.readByte();
1268 return YearMonth.of(year, month);
1269 }
1270
1271 }