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