1 /*
2 * Copyright (c) 2012, 2023, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 /*
27 * This file is available under and governed by the GNU General Public
28 * License version 2 only, as published by the Free Software Foundation.
29 * However, the following notice accompanied the original version of this
30 * file:
31 *
32 * Copyright (c) 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.Serializable;
82 import java.time.chrono.Chronology;
83 import java.time.chrono.IsoChronology;
84 import java.time.format.DateTimeFormatter;
85 import java.time.format.DateTimeFormatterBuilder;
86 import java.time.format.DateTimeParseException;
87 import java.time.format.SignStyle;
88 import java.time.temporal.ChronoField;
89 import java.time.temporal.ChronoUnit;
90 import java.time.temporal.Temporal;
91 import java.time.temporal.TemporalAccessor;
92 import java.time.temporal.TemporalAdjuster;
93 import java.time.temporal.TemporalAmount;
94 import java.time.temporal.TemporalField;
95 import java.time.temporal.TemporalQueries;
96 import java.time.temporal.TemporalQuery;
97 import java.time.temporal.TemporalUnit;
98 import java.time.temporal.UnsupportedTemporalTypeException;
99 import java.time.temporal.ValueRange;
100 import java.util.Objects;
101
102 /**
103 * A year-month in the ISO-8601 calendar system, such as {@code 2007-12}.
104 * <p>
105 * {@code YearMonth} is an immutable date-time object that represents the combination
106 * of a year and month. Any field that can be derived from a year and month, such as
107 * quarter-of-year, can be obtained.
108 * <p>
109 * This class does not store or represent a day, time or time-zone.
110 * For example, the value "October 2007" can be stored in a {@code YearMonth}.
111 * <p>
112 * The ISO-8601 calendar system is the modern civil calendar system used today
113 * in most of the world. It is equivalent to the proleptic Gregorian calendar
114 * system, in which today's rules for leap years are applied for all time.
115 * For most applications written today, the ISO-8601 rules are entirely suitable.
116 * However, any application that makes use of historical dates, and requires them
117 * to be accurate will find the ISO-8601 approach unsuitable.
118 * <p>
119 * This is a <a href="{@docRoot}/java.base/java/lang/doc-files/ValueBased.html">value-based</a>
120 * class; programmers should treat instances that are {@linkplain #equals(Object) equal}
121 * as interchangeable and should not use instances for synchronization, mutexes, or
122 * with {@linkplain java.lang.ref.Reference object references}.
123 *
124 * <div class="preview-block">
125 * <div class="preview-comment">
126 * When preview features are enabled, {@code YearMonth} is a {@linkplain Class#isValue value class}.
127 * Use of value class instances for synchronization, mutexes, or with
128 * {@linkplain java.lang.ref.Reference object references} result in
129 * {@link IdentityException}.
130 * </div>
131 * </div>
132 *
133 * @implSpec
134 * This class is immutable and thread-safe.
135 *
136 * @since 1.8
137 */
138 @jdk.internal.ValueBased
139 @jdk.internal.MigratedValueClass
140 public final class YearMonth
141 implements Temporal, TemporalAdjuster, Comparable<YearMonth>, Serializable {
142
143 /**
144 * Serialization version.
145 */
146 @java.io.Serial
147 private static final long serialVersionUID = 4183400860270640070L;
148 /**
149 * Parser.
150 */
151 private static final DateTimeFormatter PARSER = new DateTimeFormatterBuilder()
152 .appendValue(YEAR, 4, 10, SignStyle.EXCEEDS_PAD)
153 .appendLiteral('-')
154 .appendValue(MONTH_OF_YEAR, 2)
155 .toFormatter();
156
157 /**
158 * The year.
159 */
160 private final int year;
161 /**
162 * The month-of-year, not null.
163 */
164 private final int month;
165
166 //-----------------------------------------------------------------------
167 /**
168 * Obtains the current year-month from the system clock in the default time-zone.
169 * <p>
170 * This will query the {@link Clock#systemDefaultZone() system clock} in the default
171 * time-zone to obtain the current year-month.
172 * <p>
173 * Using this method will prevent the ability to use an alternate clock for testing
174 * because the clock is hard-coded.
175 *
176 * @return the current year-month using the system clock and default time-zone, not null
177 */
178 public static YearMonth now() {
179 return now(Clock.systemDefaultZone());
180 }
181
182 /**
183 * Obtains the current year-month from the system clock in the specified time-zone.
184 * <p>
185 * This will query the {@link Clock#system(ZoneId) system clock} to obtain the current year-month.
186 * Specifying the time-zone avoids dependence on the default time-zone.
187 * <p>
188 * Using this method will prevent the ability to use an alternate clock for testing
189 * because the clock is hard-coded.
190 *
191 * @param zone the zone ID to use, not null
192 * @return the current year-month using the system clock, not null
193 */
194 public static YearMonth now(ZoneId zone) {
195 return now(Clock.system(zone));
196 }
197
198 /**
199 * Obtains the current year-month from the specified clock.
200 * <p>
201 * This will query the specified clock to obtain the current year-month.
202 * Using this method allows the use of an alternate clock for testing.
203 * The alternate clock may be introduced using {@link Clock dependency injection}.
204 *
205 * @param clock the clock to use, not null
206 * @return the current year-month, not null
207 */
208 public static YearMonth now(Clock clock) {
209 final LocalDate now = LocalDate.now(clock); // called once
210 return YearMonth.of(now.getYear(), now.getMonth());
211 }
212
213 //-----------------------------------------------------------------------
214 /**
215 * Obtains an instance of {@code YearMonth} from a year and month.
216 *
217 * @param year the year to represent, from MIN_YEAR to MAX_YEAR
218 * @param month the month-of-year to represent, not null
219 * @return the year-month, not null
220 * @throws DateTimeException if the year value is invalid
221 */
222 public static YearMonth of(int year, Month month) {
223 Objects.requireNonNull(month, "month");
224 return of(year, month.getValue());
225 }
226
227 /**
228 * Obtains an instance of {@code YearMonth} from a year and month.
229 *
230 * @param year the year to represent, from MIN_YEAR to MAX_YEAR
231 * @param month the month-of-year to represent, from 1 (January) to 12 (December)
232 * @return the year-month, not null
233 * @throws DateTimeException if either field value is invalid
234 */
235 public static YearMonth of(int year, int month) {
236 YEAR.checkValidValue(year);
237 MONTH_OF_YEAR.checkValidValue(month);
238 return new YearMonth(year, month);
239 }
240
241 //-----------------------------------------------------------------------
242 /**
243 * Obtains an instance of {@code YearMonth} from a temporal object.
244 * <p>
245 * This obtains a year-month based on the specified temporal.
246 * A {@code TemporalAccessor} represents an arbitrary set of date and time information,
247 * which this factory converts to an instance of {@code YearMonth}.
248 * <p>
249 * The conversion extracts the {@link ChronoField#YEAR YEAR} and
250 * {@link ChronoField#MONTH_OF_YEAR MONTH_OF_YEAR} fields.
251 * The extraction is only permitted if the temporal object has an ISO
252 * chronology, or can be converted to a {@code LocalDate}.
253 * <p>
254 * This method matches the signature of the functional interface {@link TemporalQuery}
255 * allowing it to be used as a query via method reference, {@code YearMonth::from}.
256 *
257 * @param temporal the temporal object to convert, not null
258 * @return the year-month, not null
259 * @throws DateTimeException if unable to convert to a {@code YearMonth}
260 */
261 public static YearMonth from(TemporalAccessor temporal) {
262 if (temporal instanceof YearMonth) {
263 return (YearMonth) temporal;
264 }
265 Objects.requireNonNull(temporal, "temporal");
266 try {
267 if (IsoChronology.INSTANCE.equals(Chronology.from(temporal)) == false) {
268 temporal = LocalDate.from(temporal);
269 }
270 return of(temporal.get(YEAR), temporal.get(MONTH_OF_YEAR));
271 } catch (DateTimeException ex) {
272 throw new DateTimeException("Unable to obtain YearMonth from TemporalAccessor: " +
273 temporal + " of type " + temporal.getClass().getName(), ex);
274 }
275 }
276
277 //-----------------------------------------------------------------------
278 /**
279 * Obtains an instance of {@code YearMonth} from a text string such as {@code 2007-12}.
280 * <p>
281 * The string must represent a valid year-month.
282 * The format must be {@code uuuu-MM}.
283 * Years outside the range 0000 to 9999 must be prefixed by the plus or minus symbol.
284 *
285 * @param text the text to parse such as "2007-12", not null
286 * @return the parsed year-month, not null
287 * @throws DateTimeParseException if the text cannot be parsed
288 */
289 public static YearMonth parse(CharSequence text) {
290 return parse(text, PARSER);
291 }
292
293 /**
294 * Obtains an instance of {@code YearMonth} from a text string using a specific formatter.
295 * <p>
296 * The text is parsed using the formatter, returning a year-month.
297 *
298 * @param text the text to parse, not null
299 * @param formatter the formatter to use, not null
300 * @return the parsed year-month, not null
301 * @throws DateTimeParseException if the text cannot be parsed
302 */
303 public static YearMonth parse(CharSequence text, DateTimeFormatter formatter) {
304 Objects.requireNonNull(formatter, "formatter");
305 return formatter.parse(text, YearMonth::from);
306 }
307
308 //-----------------------------------------------------------------------
309 /**
310 * Constructor.
311 *
312 * @param year the year to represent, validated from MIN_YEAR to MAX_YEAR
313 * @param month the month-of-year to represent, validated from 1 (January) to 12 (December)
314 */
315 private YearMonth(int year, int month) {
316 this.year = year;
317 this.month = month;
318 }
319
320 /**
321 * Returns a copy of this year-month with the new year and month, checking
322 * to see if a new object is in fact required.
323 *
324 * @param newYear the year to represent, validated from MIN_YEAR to MAX_YEAR
325 * @param newMonth the month-of-year to represent, validated not null
326 * @return the year-month, not null
327 */
328 private YearMonth with(int newYear, int newMonth) {
329 if (year == newYear && month == newMonth) {
330 return this;
331 }
332 return new YearMonth(newYear, newMonth);
333 }
334
335 //-----------------------------------------------------------------------
336 /**
337 * Checks if the specified field is supported.
338 * <p>
339 * This checks if this year-month can be queried for the specified field.
340 * If false, then calling the {@link #range(TemporalField) range},
341 * {@link #get(TemporalField) get} and {@link #with(TemporalField, long)}
342 * methods will throw an exception.
343 * <p>
344 * If the field is a {@link ChronoField} then the query is implemented here.
345 * The supported fields are:
346 * <ul>
347 * <li>{@code MONTH_OF_YEAR}
348 * <li>{@code PROLEPTIC_MONTH}
349 * <li>{@code YEAR_OF_ERA}
350 * <li>{@code YEAR}
351 * <li>{@code ERA}
352 * </ul>
353 * All other {@code ChronoField} instances will return false.
354 * <p>
355 * If the field is not a {@code ChronoField}, then the result of this method
356 * is obtained by invoking {@code TemporalField.isSupportedBy(TemporalAccessor)}
357 * passing {@code this} as the argument.
358 * Whether the field is supported is determined by the field.
359 *
360 * @param field the field to check, null returns false
361 * @return true if the field is supported on this year-month, false if not
362 */
363 @Override
364 public boolean isSupported(TemporalField field) {
365 if (field instanceof ChronoField) {
366 return field == YEAR || field == MONTH_OF_YEAR ||
367 field == PROLEPTIC_MONTH || field == YEAR_OF_ERA || field == ERA;
368 }
369 return field != null && field.isSupportedBy(this);
370 }
371
372 /**
373 * Checks if the specified unit is supported.
374 * <p>
375 * This checks if the specified unit can be added to, or subtracted from, this year-month.
376 * If false, then calling the {@link #plus(long, TemporalUnit)} and
377 * {@link #minus(long, TemporalUnit) minus} methods will throw an exception.
378 * <p>
379 * If the unit is a {@link ChronoUnit} then the query is implemented here.
380 * The supported units are:
381 * <ul>
382 * <li>{@code MONTHS}
383 * <li>{@code YEARS}
384 * <li>{@code DECADES}
385 * <li>{@code CENTURIES}
386 * <li>{@code MILLENNIA}
387 * <li>{@code ERAS}
388 * </ul>
389 * All other {@code ChronoUnit} instances will return false.
390 * <p>
391 * If the unit is not a {@code ChronoUnit}, then the result of this method
392 * is obtained by invoking {@code TemporalUnit.isSupportedBy(Temporal)}
393 * passing {@code this} as the argument.
394 * Whether the unit is supported is determined by the unit.
395 *
396 * @param unit the unit to check, null returns false
397 * @return true if the unit can be added/subtracted, false if not
398 */
399 @Override
400 public boolean isSupported(TemporalUnit unit) {
401 if (unit instanceof ChronoUnit) {
402 return unit == MONTHS || unit == YEARS || unit == DECADES || unit == CENTURIES || unit == MILLENNIA || unit == ERAS;
403 }
404 return unit != null && unit.isSupportedBy(this);
405 }
406
407 //-----------------------------------------------------------------------
408 /**
409 * Gets the range of valid values for the specified field.
410 * <p>
411 * The range object expresses the minimum and maximum valid values for a field.
412 * This year-month is used to enhance the accuracy of the returned range.
413 * If it is not possible to return the range, because the field is not supported
414 * or for some other reason, an exception is thrown.
415 * <p>
416 * If the field is a {@link ChronoField} then the query is implemented here.
417 * The {@link #isSupported(TemporalField) supported fields} will return
418 * appropriate range instances.
419 * All other {@code ChronoField} instances will throw an {@code UnsupportedTemporalTypeException}.
420 * <p>
421 * If the field is not a {@code ChronoField}, then the result of this method
422 * is obtained by invoking {@code TemporalField.rangeRefinedBy(TemporalAccessor)}
423 * passing {@code this} as the argument.
424 * Whether the range can be obtained is determined by the field.
425 *
426 * @param field the field to query the range for, not null
427 * @return the range of valid values for the field, not null
428 * @throws DateTimeException if the range for the field cannot be obtained
429 * @throws UnsupportedTemporalTypeException if the field is not supported
430 */
431 @Override
432 public ValueRange range(TemporalField field) {
433 if (field == YEAR_OF_ERA) {
434 return (getYear() <= 0 ? ValueRange.of(1, Year.MAX_VALUE + 1) : ValueRange.of(1, Year.MAX_VALUE));
435 }
436 return Temporal.super.range(field);
437 }
438
439 /**
440 * Gets the value of the specified field from this year-month as an {@code int}.
441 * <p>
442 * This queries this year-month for the value of the specified field.
443 * The returned value will always be within the valid range of values for the field.
444 * If it is not possible to return the value, because the field is not supported
445 * or for some other reason, an exception is thrown.
446 * <p>
447 * If the field is a {@link ChronoField} then the query is implemented here.
448 * The {@link #isSupported(TemporalField) supported fields} will return valid
449 * values based on this year-month, except {@code PROLEPTIC_MONTH} which is too
450 * large to fit in an {@code int} and throw a {@code DateTimeException}.
451 * All other {@code ChronoField} instances will throw an {@code UnsupportedTemporalTypeException}.
452 * <p>
453 * If the field is not a {@code ChronoField}, then the result of this method
454 * is obtained by invoking {@code TemporalField.getFrom(TemporalAccessor)}
455 * passing {@code this} as the argument. Whether the value can be obtained,
456 * and what the value represents, is determined by the field.
457 *
458 * @param field the field to get, not null
459 * @return the value for the field
460 * @throws DateTimeException if a value for the field cannot be obtained or
461 * the value is outside the range of valid values for the field
462 * @throws UnsupportedTemporalTypeException if the field is not supported or
463 * the range of values exceeds an {@code int}
464 * @throws ArithmeticException if numeric overflow occurs
465 */
466 @Override // override for Javadoc
467 public int get(TemporalField field) {
468 return range(field).checkValidIntValue(getLong(field), field);
469 }
470
471 /**
472 * Gets the value of the specified field from this year-month as a {@code long}.
473 * <p>
474 * This queries this year-month for the value of the specified field.
475 * If it is not possible to return the value, because the field is not supported
476 * or for some other reason, an exception is thrown.
477 * <p>
478 * If the field is a {@link ChronoField} then the query is implemented here.
479 * The {@link #isSupported(TemporalField) supported fields} will return valid
480 * values based on this year-month.
481 * All other {@code ChronoField} instances will throw an {@code UnsupportedTemporalTypeException}.
482 * <p>
483 * If the field is not a {@code ChronoField}, then the result of this method
484 * is obtained by invoking {@code TemporalField.getFrom(TemporalAccessor)}
485 * passing {@code this} as the argument. Whether the value can be obtained,
486 * and what the value represents, is determined by the field.
487 *
488 * @param field the field to get, not null
489 * @return the value for the field
490 * @throws DateTimeException if a value for the field cannot be obtained
491 * @throws UnsupportedTemporalTypeException if the field is not supported
492 * @throws ArithmeticException if numeric overflow occurs
493 */
494 @Override
495 public long getLong(TemporalField field) {
496 if (field instanceof ChronoField chronoField) {
497 return switch (chronoField) {
498 case MONTH_OF_YEAR -> month;
499 case PROLEPTIC_MONTH -> getProlepticMonth();
500 case YEAR_OF_ERA -> (year < 1 ? 1 - year : year);
501 case YEAR -> year;
502 case ERA -> (year < 1 ? 0 : 1);
503 default -> throw new UnsupportedTemporalTypeException("Unsupported field: " + field);
504 };
505 }
506 return field.getFrom(this);
507 }
508
509 private long getProlepticMonth() {
510 return (year * 12L + month - 1);
511 }
512
513 //-----------------------------------------------------------------------
514 /**
515 * Gets the year field.
516 * <p>
517 * This method returns the primitive {@code int} value for the year.
518 * <p>
519 * The year returned by this method is proleptic as per {@code get(YEAR)}.
520 *
521 * @return the year, from MIN_YEAR to MAX_YEAR
522 */
523 public int getYear() {
524 return year;
525 }
526
527 /**
528 * Gets the month-of-year field from 1 to 12.
529 * <p>
530 * This method returns the month as an {@code int} from 1 to 12.
531 * Application code is frequently clearer if the enum {@link Month}
532 * is used by calling {@link #getMonth()}.
533 *
534 * @return the month-of-year, from 1 to 12
535 * @see #getMonth()
536 */
537 public int getMonthValue() {
538 return month;
539 }
540
541 /**
542 * Gets the month-of-year field using the {@code Month} enum.
543 * <p>
544 * This method returns the enum {@link Month} for the month.
545 * This avoids confusion as to what {@code int} values mean.
546 * If you need access to the primitive {@code int} value then the enum
547 * provides the {@link Month#getValue() int value}.
548 *
549 * @return the month-of-year, not null
550 * @see #getMonthValue()
551 */
552 public Month getMonth() {
553 return Month.of(month);
554 }
555
556 //-----------------------------------------------------------------------
557 /**
558 * Checks if the year is a leap year, according to the ISO proleptic
559 * calendar system rules.
560 * <p>
561 * This method applies the current rules for leap years across the whole time-line.
562 * In general, a year is a leap year if it is divisible by four without
563 * remainder. However, years divisible by 100, are not leap years, with
564 * the exception of years divisible by 400 which are.
565 * <p>
566 * For example, 1904 is a leap year it is divisible by 4.
567 * 1900 was not a leap year as it is divisible by 100, however 2000 was a
568 * leap year as it is divisible by 400.
569 * <p>
570 * The calculation is proleptic - applying the same rules into the far future and far past.
571 * This is historically inaccurate, but is correct for the ISO-8601 standard.
572 *
573 * @return true if the year is leap, false otherwise
574 */
575 public boolean isLeapYear() {
576 return IsoChronology.INSTANCE.isLeapYear(year);
577 }
578
579 /**
580 * Checks if the day-of-month is valid for this year-month.
581 * <p>
582 * This method checks whether this year and month and the input day form
583 * a valid date.
584 *
585 * @param dayOfMonth the day-of-month to validate, from 1 to 31, invalid value returns false
586 * @return true if the day is valid for this year-month
587 */
588 public boolean isValidDay(int dayOfMonth) {
589 return dayOfMonth >= 1 && dayOfMonth <= lengthOfMonth();
590 }
591
592 /**
593 * Returns the length of the month, taking account of the year.
594 * <p>
595 * This returns the length of the month in days.
596 * For example, a date in January would return 31.
597 *
598 * @return the length of the month in days, from 28 to 31
599 */
600 public int lengthOfMonth() {
601 return getMonth().length(isLeapYear());
602 }
603
604 /**
605 * Returns the length of the year.
606 * <p>
607 * This returns the length of the year in days, either 365 or 366.
608 *
609 * @return 366 if the year is leap, 365 otherwise
610 */
611 public int lengthOfYear() {
612 return (isLeapYear() ? 366 : 365);
613 }
614
615 //-----------------------------------------------------------------------
616 /**
617 * Returns an adjusted copy of this year-month.
618 * <p>
619 * This returns a {@code YearMonth}, based on this one, with the year-month adjusted.
620 * The adjustment takes place using the specified adjuster strategy object.
621 * Read the documentation of the adjuster to understand what adjustment will be made.
622 * <p>
623 * A simple adjuster might simply set the one of the fields, such as the year field.
624 * A more complex adjuster might set the year-month to the next month that
625 * Halley's comet will pass the Earth.
626 * <p>
627 * The result of this method is obtained by invoking the
628 * {@link TemporalAdjuster#adjustInto(Temporal)} method on the
629 * specified adjuster passing {@code this} as the argument.
630 * <p>
631 * This instance is immutable and unaffected by this method call.
632 *
633 * @param adjuster the adjuster to use, not null
634 * @return a {@code YearMonth} based on {@code this} with the adjustment made, not null
635 * @throws DateTimeException if the adjustment cannot be made
636 * @throws ArithmeticException if numeric overflow occurs
637 */
638 @Override
639 public YearMonth with(TemporalAdjuster adjuster) {
640 return (YearMonth) adjuster.adjustInto(this);
641 }
642
643 /**
644 * Returns a copy of this year-month with the specified field set to a new value.
645 * <p>
646 * This returns a {@code YearMonth}, based on this one, with the value
647 * for the specified field changed.
648 * This can be used to change any supported field, such as the year or month.
649 * If it is not possible to set the value, because the field is not supported or for
650 * some other reason, an exception is thrown.
651 * <p>
652 * If the field is a {@link ChronoField} then the adjustment is implemented here.
653 * The supported fields behave as follows:
654 * <ul>
655 * <li>{@code MONTH_OF_YEAR} -
656 * Returns a {@code YearMonth} with the specified month-of-year.
657 * The year will be unchanged.
658 * <li>{@code PROLEPTIC_MONTH} -
659 * Returns a {@code YearMonth} with the specified proleptic-month.
660 * This completely replaces the year and month of this object.
661 * <li>{@code YEAR_OF_ERA} -
662 * Returns a {@code YearMonth} with the specified year-of-era
663 * The month and era will be unchanged.
664 * <li>{@code YEAR} -
665 * Returns a {@code YearMonth} with the specified year.
666 * The month will be unchanged.
667 * <li>{@code ERA} -
668 * Returns a {@code YearMonth} with the specified era.
669 * The month and year-of-era will be unchanged.
670 * </ul>
671 * <p>
672 * In all cases, if the new value is outside the valid range of values for the field
673 * then a {@code DateTimeException} will be thrown.
674 * <p>
675 * All other {@code ChronoField} instances will throw an {@code UnsupportedTemporalTypeException}.
676 * <p>
677 * If the field is not a {@code ChronoField}, then the result of this method
678 * is obtained by invoking {@code TemporalField.adjustInto(Temporal, long)}
679 * passing {@code this} as the argument. In this case, the field determines
680 * whether and how to adjust the instant.
681 * <p>
682 * This instance is immutable and unaffected by this method call.
683 *
684 * @param field the field to set in the result, not null
685 * @param newValue the new value of the field in the result
686 * @return a {@code YearMonth} based on {@code this} with the specified field set, not null
687 * @throws DateTimeException if the field cannot be set
688 * @throws UnsupportedTemporalTypeException if the field is not supported
689 * @throws ArithmeticException if numeric overflow occurs
690 */
691 @Override
692 public YearMonth with(TemporalField field, long newValue) {
693 if (field instanceof ChronoField chronoField) {
694 chronoField.checkValidValue(newValue);
695 return switch (chronoField) {
696 case MONTH_OF_YEAR -> withMonth((int) newValue);
697 case PROLEPTIC_MONTH -> plusMonths(newValue - getProlepticMonth());
698 case YEAR_OF_ERA -> withYear((int) (year < 1 ? 1 - newValue : newValue));
699 case YEAR -> withYear((int) newValue);
700 case ERA -> (getLong(ERA) == newValue ? this : withYear(1 - year));
701 default -> throw new UnsupportedTemporalTypeException("Unsupported field: " + field);
702 };
703 }
704 return field.adjustInto(this, newValue);
705 }
706
707 //-----------------------------------------------------------------------
708 /**
709 * Returns a copy of this {@code YearMonth} with the year altered.
710 * <p>
711 * This instance is immutable and unaffected by this method call.
712 *
713 * @param year the year to set in the returned year-month, from MIN_YEAR to MAX_YEAR
714 * @return a {@code YearMonth} based on this year-month with the requested year, not null
715 * @throws DateTimeException if the year value is invalid
716 */
717 public YearMonth withYear(int year) {
718 YEAR.checkValidValue(year);
719 return with(year, month);
720 }
721
722 /**
723 * Returns a copy of this {@code YearMonth} with the month-of-year altered.
724 * <p>
725 * This instance is immutable and unaffected by this method call.
726 *
727 * @param month the month-of-year to set in the returned year-month, from 1 (January) to 12 (December)
728 * @return a {@code YearMonth} based on this year-month with the requested month, not null
729 * @throws DateTimeException if the month-of-year value is invalid
730 */
731 public YearMonth withMonth(int month) {
732 MONTH_OF_YEAR.checkValidValue(month);
733 return with(year, month);
734 }
735
736 //-----------------------------------------------------------------------
737 /**
738 * Returns a copy of this year-month with the specified amount added.
739 * <p>
740 * This returns a {@code YearMonth}, based on this one, with the specified amount added.
741 * The amount is typically {@link Period} but may be any other type implementing
742 * the {@link TemporalAmount} interface.
743 * <p>
744 * The calculation is delegated to the amount object by calling
745 * {@link TemporalAmount#addTo(Temporal)}. The amount implementation is free
746 * to implement the addition in any way it wishes, however it typically
747 * calls back to {@link #plus(long, TemporalUnit)}. Consult the documentation
748 * of the amount implementation to determine if it can be successfully added.
749 * <p>
750 * This instance is immutable and unaffected by this method call.
751 *
752 * @param amountToAdd the amount to add, not null
753 * @return a {@code YearMonth} based on this year-month with the addition made, not null
754 * @throws DateTimeException if the addition cannot be made
755 * @throws ArithmeticException if numeric overflow occurs
756 */
757 @Override
758 public YearMonth plus(TemporalAmount amountToAdd) {
759 return (YearMonth) amountToAdd.addTo(this);
760 }
761
762 /**
763 * Returns a copy of this year-month with the specified amount added.
764 * <p>
765 * This returns a {@code YearMonth}, based on this one, with the amount
766 * in terms of the unit added. If it is not possible to add the amount, because the
767 * unit is not supported or for some other reason, an exception is thrown.
768 * <p>
769 * If the field is a {@link ChronoUnit} then the addition is implemented here.
770 * The supported fields behave as follows:
771 * <ul>
772 * <li>{@code MONTHS} -
773 * Returns a {@code YearMonth} with the specified number of months added.
774 * This is equivalent to {@link #plusMonths(long)}.
775 * <li>{@code YEARS} -
776 * Returns a {@code YearMonth} with the specified number of years added.
777 * This is equivalent to {@link #plusYears(long)}.
778 * <li>{@code DECADES} -
779 * Returns a {@code YearMonth} with the specified number of decades added.
780 * This is equivalent to calling {@link #plusYears(long)} with the amount
781 * multiplied by 10.
782 * <li>{@code CENTURIES} -
783 * Returns a {@code YearMonth} with the specified number of centuries added.
784 * This is equivalent to calling {@link #plusYears(long)} with the amount
785 * multiplied by 100.
786 * <li>{@code MILLENNIA} -
787 * Returns a {@code YearMonth} with the specified number of millennia added.
788 * This is equivalent to calling {@link #plusYears(long)} with the amount
789 * multiplied by 1,000.
790 * <li>{@code ERAS} -
791 * Returns a {@code YearMonth} with the specified number of eras added.
792 * Only two eras are supported so the amount must be one, zero or minus one.
793 * If the amount is non-zero then the year is changed such that the year-of-era
794 * is unchanged.
795 * </ul>
796 * <p>
797 * All other {@code ChronoUnit} instances will throw an {@code UnsupportedTemporalTypeException}.
798 * <p>
799 * If the field is not a {@code ChronoUnit}, then the result of this method
800 * is obtained by invoking {@code TemporalUnit.addTo(Temporal, long)}
801 * passing {@code this} as the argument. In this case, the unit determines
802 * whether and how to perform the addition.
803 * <p>
804 * This instance is immutable and unaffected by this method call.
805 *
806 * @param amountToAdd the amount of the unit to add to the result, may be negative
807 * @param unit the unit of the amount to add, not null
808 * @return a {@code YearMonth} based on this year-month with the specified amount added, not null
809 * @throws DateTimeException if the addition cannot be made
810 * @throws UnsupportedTemporalTypeException if the unit is not supported
811 * @throws ArithmeticException if numeric overflow occurs
812 */
813 @Override
814 public YearMonth plus(long amountToAdd, TemporalUnit unit) {
815 if (unit instanceof ChronoUnit chronoUnit) {
816 return switch (chronoUnit) {
817 case MONTHS -> plusMonths(amountToAdd);
818 case YEARS -> plusYears(amountToAdd);
819 case DECADES -> plusYears(Math.multiplyExact(amountToAdd, 10));
820 case CENTURIES -> plusYears(Math.multiplyExact(amountToAdd, 100));
821 case MILLENNIA -> plusYears(Math.multiplyExact(amountToAdd, 1000));
822 case ERAS -> with(ERA, Math.addExact(getLong(ERA), amountToAdd));
823 default -> throw new UnsupportedTemporalTypeException("Unsupported unit: " + unit);
824 };
825 }
826 return unit.addTo(this, amountToAdd);
827 }
828
829 /**
830 * Returns a copy of this {@code YearMonth} with the specified number of years added.
831 * <p>
832 * This instance is immutable and unaffected by this method call.
833 *
834 * @param yearsToAdd the years to add, may be negative
835 * @return a {@code YearMonth} based on this year-month with the years added, not null
836 * @throws DateTimeException if the result exceeds the supported range
837 */
838 public YearMonth plusYears(long yearsToAdd) {
839 if (yearsToAdd == 0) {
840 return this;
841 }
842 int newYear = YEAR.checkValidIntValue(year + yearsToAdd); // safe overflow
843 return with(newYear, month);
844 }
845
846 /**
847 * Returns a copy of this {@code YearMonth} with the specified number of months added.
848 * <p>
849 * This instance is immutable and unaffected by this method call.
850 *
851 * @param monthsToAdd the months to add, may be negative
852 * @return a {@code YearMonth} based on this year-month with the months added, not null
853 * @throws DateTimeException if the result exceeds the supported range
854 */
855 public YearMonth plusMonths(long monthsToAdd) {
856 if (monthsToAdd == 0) {
857 return this;
858 }
859 long monthCount = year * 12L + (month - 1);
860 long calcMonths = monthCount + monthsToAdd; // safe overflow
861 int newYear = YEAR.checkValidIntValue(Math.floorDiv(calcMonths, 12));
862 int newMonth = Math.floorMod(calcMonths, 12) + 1;
863 return with(newYear, newMonth);
864 }
865
866 //-----------------------------------------------------------------------
867 /**
868 * Returns a copy of this year-month with the specified amount subtracted.
869 * <p>
870 * This returns a {@code YearMonth}, based on this one, with the specified amount subtracted.
871 * The amount is typically {@link Period} but may be any other type implementing
872 * the {@link TemporalAmount} interface.
873 * <p>
874 * The calculation is delegated to the amount object by calling
875 * {@link TemporalAmount#subtractFrom(Temporal)}. The amount implementation is free
876 * to implement the subtraction in any way it wishes, however it typically
877 * calls back to {@link #minus(long, TemporalUnit)}. Consult the documentation
878 * of the amount implementation to determine if it can be successfully subtracted.
879 * <p>
880 * This instance is immutable and unaffected by this method call.
881 *
882 * @param amountToSubtract the amount to subtract, not null
883 * @return a {@code YearMonth} based on this year-month with the subtraction made, not null
884 * @throws DateTimeException if the subtraction cannot be made
885 * @throws ArithmeticException if numeric overflow occurs
886 */
887 @Override
888 public YearMonth minus(TemporalAmount amountToSubtract) {
889 return (YearMonth) amountToSubtract.subtractFrom(this);
890 }
891
892 /**
893 * Returns a copy of this year-month with the specified amount subtracted.
894 * <p>
895 * This returns a {@code YearMonth}, based on this one, with the amount
896 * in terms of the unit subtracted. If it is not possible to subtract the amount,
897 * because the unit is not supported or for some other reason, an exception is thrown.
898 * <p>
899 * This method is equivalent to {@link #plus(long, TemporalUnit)} with the amount negated.
900 * See that method for a full description of how addition, and thus subtraction, works.
901 * <p>
902 * This instance is immutable and unaffected by this method call.
903 *
904 * @param amountToSubtract the amount of the unit to subtract from the result, may be negative
905 * @param unit the unit of the amount to subtract, not null
906 * @return a {@code YearMonth} based on this year-month with the specified amount subtracted, not null
907 * @throws DateTimeException if the subtraction cannot be made
908 * @throws UnsupportedTemporalTypeException if the unit is not supported
909 * @throws ArithmeticException if numeric overflow occurs
910 */
911 @Override
912 public YearMonth minus(long amountToSubtract, TemporalUnit unit) {
913 return (amountToSubtract == Long.MIN_VALUE ? plus(Long.MAX_VALUE, unit).plus(1, unit) : plus(-amountToSubtract, unit));
914 }
915
916 /**
917 * Returns a copy of this {@code YearMonth} with the specified number of years subtracted.
918 * <p>
919 * This instance is immutable and unaffected by this method call.
920 *
921 * @param yearsToSubtract the years to subtract, may be negative
922 * @return a {@code YearMonth} based on this year-month with the years subtracted, not null
923 * @throws DateTimeException if the result exceeds the supported range
924 */
925 public YearMonth minusYears(long yearsToSubtract) {
926 return (yearsToSubtract == Long.MIN_VALUE ? plusYears(Long.MAX_VALUE).plusYears(1) : plusYears(-yearsToSubtract));
927 }
928
929 /**
930 * Returns a copy of this {@code YearMonth} with the specified number of months subtracted.
931 * <p>
932 * This instance is immutable and unaffected by this method call.
933 *
934 * @param monthsToSubtract the months to subtract, may be negative
935 * @return a {@code YearMonth} based on this year-month with the months subtracted, not null
936 * @throws DateTimeException if the result exceeds the supported range
937 */
938 public YearMonth minusMonths(long monthsToSubtract) {
939 return (monthsToSubtract == Long.MIN_VALUE ? plusMonths(Long.MAX_VALUE).plusMonths(1) : plusMonths(-monthsToSubtract));
940 }
941
942 //-----------------------------------------------------------------------
943 /**
944 * Queries this year-month using the specified query.
945 * <p>
946 * This queries this year-month using the specified query strategy object.
947 * The {@code TemporalQuery} object defines the logic to be used to
948 * obtain the result. Read the documentation of the query to understand
949 * what the result of this method will be.
950 * <p>
951 * The result of this method is obtained by invoking the
952 * {@link TemporalQuery#queryFrom(TemporalAccessor)} method on the
953 * specified query passing {@code this} as the argument.
954 *
955 * @param <R> the type of the result
956 * @param query the query to invoke, not null
957 * @return the query result, null may be returned (defined by the query)
958 * @throws DateTimeException if unable to query (defined by the query)
959 * @throws ArithmeticException if numeric overflow occurs (defined by the query)
960 */
961 @SuppressWarnings("unchecked")
962 @Override
963 public <R> R query(TemporalQuery<R> query) {
964 if (query == TemporalQueries.chronology()) {
965 return (R) IsoChronology.INSTANCE;
966 } else if (query == TemporalQueries.precision()) {
967 return (R) MONTHS;
968 }
969 return Temporal.super.query(query);
970 }
971
972 /**
973 * Adjusts the specified temporal object to have this year-month.
974 * <p>
975 * This returns a temporal object of the same observable type as the input
976 * with the year and month changed to be the same as this.
977 * <p>
978 * The adjustment is equivalent to using {@link Temporal#with(TemporalField, long)}
979 * passing {@link ChronoField#PROLEPTIC_MONTH} as the field.
980 * If the specified temporal object does not use the ISO calendar system then
981 * a {@code DateTimeException} is thrown.
982 * <p>
983 * In most cases, it is clearer to reverse the calling pattern by using
984 * {@link Temporal#with(TemporalAdjuster)}:
985 * <pre>
986 * // these two lines are equivalent, but the second approach is recommended
987 * temporal = thisYearMonth.adjustInto(temporal);
988 * temporal = temporal.with(thisYearMonth);
989 * </pre>
990 * <p>
991 * This instance is immutable and unaffected by this method call.
992 *
993 * @param temporal the target object to be adjusted, not null
994 * @return the adjusted object, not null
995 * @throws DateTimeException if unable to make the adjustment
996 * @throws ArithmeticException if numeric overflow occurs
997 */
998 @Override
999 public Temporal adjustInto(Temporal temporal) {
1000 if (Chronology.from(temporal).equals(IsoChronology.INSTANCE) == false) {
1001 throw new DateTimeException("Adjustment only supported on ISO date-time");
1002 }
1003 return temporal.with(PROLEPTIC_MONTH, getProlepticMonth());
1004 }
1005
1006 /**
1007 * Calculates the amount of time until another year-month in terms of the specified unit.
1008 * <p>
1009 * This calculates the amount of time between two {@code YearMonth}
1010 * objects in terms of a single {@code TemporalUnit}.
1011 * The start and end points are {@code this} and the specified year-month.
1012 * The result will be negative if the end is before the start.
1013 * The {@code Temporal} passed to this method is converted to a
1014 * {@code YearMonth} using {@link #from(TemporalAccessor)}.
1015 * For example, the amount in years between two year-months can be calculated
1016 * using {@code startYearMonth.until(endYearMonth, YEARS)}.
1017 * <p>
1018 * The calculation returns a whole number, representing the number of
1019 * complete units between the two year-months.
1020 * For example, the amount in decades between 2012-06 and 2032-05
1021 * will only be one decade as it is one month short of two decades.
1022 * <p>
1023 * There are two equivalent ways of using this method.
1024 * The first is to invoke this method.
1025 * The second is to use {@link TemporalUnit#between(Temporal, Temporal)}:
1026 * <pre>
1027 * // these two lines are equivalent
1028 * amount = start.until(end, MONTHS);
1029 * amount = MONTHS.between(start, end);
1030 * </pre>
1031 * The choice should be made based on which makes the code more readable.
1032 * <p>
1033 * The calculation is implemented in this method for {@link ChronoUnit}.
1034 * The units {@code MONTHS}, {@code YEARS}, {@code DECADES},
1035 * {@code CENTURIES}, {@code MILLENNIA} and {@code ERAS} are supported.
1036 * Other {@code ChronoUnit} values will throw an exception.
1037 * <p>
1038 * If the unit is not a {@code ChronoUnit}, then the result of this method
1039 * is obtained by invoking {@code TemporalUnit.between(Temporal, Temporal)}
1040 * passing {@code this} as the first argument and the converted input temporal
1041 * as the second argument.
1042 * <p>
1043 * This instance is immutable and unaffected by this method call.
1044 *
1045 * @param endExclusive the end date, exclusive, which is converted to a {@code YearMonth}, not null
1046 * @param unit the unit to measure the amount in, not null
1047 * @return the amount of time between this year-month and the end year-month
1048 * @throws DateTimeException if the amount cannot be calculated, or the end
1049 * temporal cannot be converted to a {@code YearMonth}
1050 * @throws UnsupportedTemporalTypeException if the unit is not supported
1051 * @throws ArithmeticException if numeric overflow occurs
1052 */
1053 @Override
1054 public long until(Temporal endExclusive, TemporalUnit unit) {
1055 YearMonth end = YearMonth.from(endExclusive);
1056 if (unit instanceof ChronoUnit chronoUnit) {
1057 long monthsUntil = end.getProlepticMonth() - getProlepticMonth(); // no overflow
1058 return switch (chronoUnit) {
1059 case MONTHS -> monthsUntil;
1060 case YEARS -> monthsUntil / 12;
1061 case DECADES -> monthsUntil / 120;
1062 case CENTURIES -> monthsUntil / 1200;
1063 case MILLENNIA -> monthsUntil / 12000;
1064 case ERAS -> end.getLong(ERA) - getLong(ERA);
1065 default -> throw new UnsupportedTemporalTypeException("Unsupported unit: " + unit);
1066 };
1067 }
1068 return unit.between(this, end);
1069 }
1070
1071 /**
1072 * Formats this year-month using the specified formatter.
1073 * <p>
1074 * This year-month will be passed to the formatter to produce a string.
1075 *
1076 * @param formatter the formatter to use, not null
1077 * @return the formatted year-month string, not null
1078 * @throws DateTimeException if an error occurs during printing
1079 */
1080 public String format(DateTimeFormatter formatter) {
1081 Objects.requireNonNull(formatter, "formatter");
1082 return formatter.format(this);
1083 }
1084
1085 //-----------------------------------------------------------------------
1086 /**
1087 * Combines this year-month with a day-of-month to create a {@code LocalDate}.
1088 * <p>
1089 * This returns a {@code LocalDate} formed from this year-month and the specified day-of-month.
1090 * <p>
1091 * The day-of-month value must be valid for the year-month.
1092 * <p>
1093 * This method can be used as part of a chain to produce a date:
1094 * <pre>
1095 * LocalDate date = year.atMonth(month).atDay(day);
1096 * </pre>
1097 *
1098 * @param dayOfMonth the day-of-month to use, from 1 to 31
1099 * @return the date formed from this year-month and the specified day, not null
1100 * @throws DateTimeException if the day is invalid for the year-month
1101 * @see #isValidDay(int)
1102 */
1103 public LocalDate atDay(int dayOfMonth) {
1104 return LocalDate.of(year, month, dayOfMonth);
1105 }
1106
1107 /**
1108 * Returns a {@code LocalDate} at the end of the month.
1109 * <p>
1110 * This returns a {@code LocalDate} based on this year-month.
1111 * The day-of-month is set to the last valid day of the month, taking
1112 * into account leap years.
1113 * <p>
1114 * This method can be used as part of a chain to produce a date:
1115 * <pre>
1116 * LocalDate date = year.atMonth(month).atEndOfMonth();
1117 * </pre>
1118 *
1119 * @return the last valid date of this year-month, not null
1120 */
1121 public LocalDate atEndOfMonth() {
1122 return LocalDate.of(year, month, lengthOfMonth());
1123 }
1124
1125 //-----------------------------------------------------------------------
1126 /**
1127 * Compares this year-month to another year-month.
1128 * <p>
1129 * The comparison is based first on the value of the year, then on the value of the month.
1130 * It is "consistent with equals", as defined by {@link Comparable}.
1131 *
1132 * @param other the other year-month to compare to, not null
1133 * @return the comparator value, that is less than zero if this is before {@code other},
1134 * zero if they are equal, greater than zero if this is after {@code other}
1135 * @see #isBefore
1136 * @see #isAfter
1137 */
1138 @Override
1139 public int compareTo(YearMonth other) {
1140 int cmp = (year - other.year);
1141 if (cmp == 0) {
1142 cmp = (month - other.month);
1143 }
1144 return cmp;
1145 }
1146
1147 /**
1148 * Checks if this year-month is after the specified year-month.
1149 *
1150 * @param other the other year-month to compare to, not null
1151 * @return true if this is after the specified year-month
1152 */
1153 public boolean isAfter(YearMonth other) {
1154 return compareTo(other) > 0;
1155 }
1156
1157 /**
1158 * Checks if this year-month is before the specified year-month.
1159 *
1160 * @param other the other year-month to compare to, not null
1161 * @return true if this point is before the specified year-month
1162 */
1163 public boolean isBefore(YearMonth other) {
1164 return compareTo(other) < 0;
1165 }
1166
1167 //-----------------------------------------------------------------------
1168 /**
1169 * Checks if this year-month is equal to another year-month.
1170 * <p>
1171 * The comparison is based on the time-line position of the year-months.
1172 *
1173 * @param obj the object to check, null returns false
1174 * @return true if this is equal to the other year-month
1175 */
1176 @Override
1177 public boolean equals(Object obj) {
1178 if (this == obj) {
1179 return true;
1180 }
1181 return (obj instanceof YearMonth other)
1182 && year == other.year
1183 && month == other.month;
1184 }
1185
1186 /**
1187 * A hash code for this year-month.
1188 *
1189 * @return a suitable hash code
1190 */
1191 @Override
1192 public int hashCode() {
1193 return year ^ (month << 27);
1194 }
1195
1196 //-----------------------------------------------------------------------
1197 /**
1198 * Outputs this year-month as a {@code String}, such as {@code 2007-12}.
1199 * <p>
1200 * The output will be in the format {@code uuuu-MM}:
1201 *
1202 * @return a string representation of this year-month, not null
1203 */
1204 @Override
1205 public String toString() {
1206 int absYear = Math.abs(year);
1207 StringBuilder buf = new StringBuilder(9);
1208 if (absYear < 1000) {
1209 if (year < 0) {
1210 buf.append(year - 10000).deleteCharAt(1);
1211 } else {
1212 buf.append(year + 10000).deleteCharAt(0);
1213 }
1214 } else {
1215 buf.append(year);
1216 }
1217 return buf.append(month < 10 ? "-0" : "-")
1218 .append(month)
1219 .toString();
1220 }
1221
1222 //-----------------------------------------------------------------------
1223 /**
1224 * Writes the object using a
1225 * <a href="{@docRoot}/serialized-form.html#java.time.Ser">dedicated serialized form</a>.
1226 * @serialData
1227 * <pre>
1228 * out.writeByte(12); // identifies a YearMonth
1229 * out.writeInt(year);
1230 * out.writeByte(month);
1231 * </pre>
1232 *
1233 * @return the instance of {@code Ser}, not null
1234 */
1235 @java.io.Serial
1236 private Object writeReplace() {
1237 return new Ser(Ser.YEAR_MONTH_TYPE, this);
1238 }
1239
1240 /**
1241 * Defend against malicious streams.
1242 *
1243 * @param s the stream to read
1244 * @throws InvalidObjectException always
1245 */
1246 @java.io.Serial
1247 private void readObject(ObjectInputStream s) throws InvalidObjectException {
1248 throw new InvalidObjectException("Deserialization via serialization delegate");
1249 }
1250
1251 void writeExternal(DataOutput out) throws IOException {
1252 out.writeInt(year);
1253 out.writeByte(month);
1254 }
1255
1256 static YearMonth readExternal(DataInput in) throws IOException {
1257 int year = in.readInt();
1258 byte month = in.readByte();
1259 return YearMonth.of(year, month);
1260 }
1261
1262 }