1 /*
2 * Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
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 *
119 * <p>
120 * This is a <a href="{@docRoot}/java/lang/doc-files/ValueBased.html">value-based</a>
121 * class; use of identity-sensitive operations (including reference equality
122 * ({@code ==}), identity hash code, or synchronization) on instances of
123 * {@code YearMonth} may have unpredictable results and should be avoided.
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 public final class YearMonth
132 implements Temporal, TemporalAdjuster, Comparable<YearMonth>, Serializable {
133
134 /**
135 * Serialization version.
136 */
137 private static final long serialVersionUID = 4183400860270640070L;
138 /**
139 * Parser.
140 */
141 private static final DateTimeFormatter PARSER = new DateTimeFormatterBuilder()
142 .appendValue(YEAR, 4, 10, SignStyle.EXCEEDS_PAD)
143 .appendLiteral('-')
144 .appendValue(MONTH_OF_YEAR, 2)
145 .toFormatter();
146
147 /**
148 * The year.
149 */
150 private final int year;
151 /**
152 * The month-of-year, not null.
153 */
154 private final int month;
155
156 //-----------------------------------------------------------------------
157 /**
158 * Obtains the current year-month from the system clock in the default time-zone.
159 * <p>
160 * This will query the {@link Clock#systemDefaultZone() system clock} in the default
161 * time-zone to obtain the current year-month.
162 * <p>
163 * Using this method will prevent the ability to use an alternate clock for testing
164 * because the clock is hard-coded.
165 *
166 * @return the current year-month using the system clock and default time-zone, not null
167 */
168 public static YearMonth now() {
169 return now(Clock.systemDefaultZone());
170 }
171
172 /**
173 * Obtains the current year-month from the system clock in the specified time-zone.
174 * <p>
175 * This will query the {@link Clock#system(ZoneId) system clock} to obtain the current year-month.
176 * Specifying the time-zone avoids dependence on the default time-zone.
177 * <p>
178 * Using this method will prevent the ability to use an alternate clock for testing
179 * because the clock is hard-coded.
180 *
181 * @param zone the zone ID to use, not null
182 * @return the current year-month using the system clock, not null
183 */
184 public static YearMonth now(ZoneId zone) {
185 return now(Clock.system(zone));
186 }
187
188 /**
189 * Obtains the current year-month from the specified clock.
190 * <p>
191 * This will query the specified clock to obtain the current year-month.
192 * Using this method allows the use of an alternate clock for testing.
193 * The alternate clock may be introduced using {@link Clock dependency injection}.
194 *
195 * @param clock the clock to use, not null
196 * @return the current year-month, not null
197 */
198 public static YearMonth now(Clock clock) {
199 final LocalDate now = LocalDate.now(clock); // called once
200 return YearMonth.of(now.getYear(), now.getMonth());
201 }
202
203 //-----------------------------------------------------------------------
204 /**
205 * Obtains an instance of {@code YearMonth} from a year and month.
206 *
207 * @param year the year to represent, from MIN_YEAR to MAX_YEAR
208 * @param month the month-of-year to represent, not null
209 * @return the year-month, not null
210 * @throws DateTimeException if the year value is invalid
211 */
212 public static YearMonth of(int year, Month month) {
213 Objects.requireNonNull(month, "month");
214 return of(year, month.getValue());
215 }
216
217 /**
218 * Obtains an instance of {@code YearMonth} from a year and month.
219 *
220 * @param year the year to represent, from MIN_YEAR to MAX_YEAR
221 * @param month the month-of-year to represent, from 1 (January) to 12 (December)
222 * @return the year-month, not null
223 * @throws DateTimeException if either field value is invalid
224 */
225 public static YearMonth of(int year, int month) {
226 YEAR.checkValidValue(year);
227 MONTH_OF_YEAR.checkValidValue(month);
228 return new YearMonth(year, month);
229 }
230
231 //-----------------------------------------------------------------------
232 /**
233 * Obtains an instance of {@code YearMonth} from a temporal object.
234 * <p>
235 * This obtains a year-month based on the specified temporal.
236 * A {@code TemporalAccessor} represents an arbitrary set of date and time information,
237 * which this factory converts to an instance of {@code YearMonth}.
238 * <p>
239 * The conversion extracts the {@link ChronoField#YEAR YEAR} and
240 * {@link ChronoField#MONTH_OF_YEAR MONTH_OF_YEAR} fields.
241 * The extraction is only permitted if the temporal object has an ISO
242 * chronology, or can be converted to a {@code LocalDate}.
243 * <p>
244 * This method matches the signature of the functional interface {@link TemporalQuery}
245 * allowing it to be used as a query via method reference, {@code YearMonth::from}.
246 *
247 * @param temporal the temporal object to convert, not null
248 * @return the year-month, not null
249 * @throws DateTimeException if unable to convert to a {@code YearMonth}
250 */
251 public static YearMonth from(TemporalAccessor temporal) {
252 if (temporal instanceof YearMonth) {
253 return (YearMonth) temporal;
254 }
255 Objects.requireNonNull(temporal, "temporal");
256 try {
257 if (IsoChronology.INSTANCE.equals(Chronology.from(temporal)) == false) {
258 temporal = LocalDate.from(temporal);
259 }
260 return of(temporal.get(YEAR), temporal.get(MONTH_OF_YEAR));
261 } catch (DateTimeException ex) {
262 throw new DateTimeException("Unable to obtain YearMonth from TemporalAccessor: " +
263 temporal + " of type " + temporal.getClass().getName(), ex);
264 }
265 }
266
267 //-----------------------------------------------------------------------
268 /**
269 * Obtains an instance of {@code YearMonth} from a text string such as {@code 2007-12}.
270 * <p>
271 * The string must represent a valid year-month.
272 * The format must be {@code uuuu-MM}.
273 * Years outside the range 0000 to 9999 must be prefixed by the plus or minus symbol.
274 *
275 * @param text the text to parse such as "2007-12", not null
276 * @return the parsed year-month, not null
277 * @throws DateTimeParseException if the text cannot be parsed
278 */
279 public static YearMonth parse(CharSequence text) {
280 return parse(text, PARSER);
281 }
282
283 /**
284 * Obtains an instance of {@code YearMonth} from a text string using a specific formatter.
285 * <p>
286 * The text is parsed using the formatter, returning a year-month.
287 *
288 * @param text the text to parse, not null
289 * @param formatter the formatter to use, not null
290 * @return the parsed year-month, not null
291 * @throws DateTimeParseException if the text cannot be parsed
292 */
293 public static YearMonth parse(CharSequence text, DateTimeFormatter formatter) {
294 Objects.requireNonNull(formatter, "formatter");
295 return formatter.parse(text, YearMonth::from);
296 }
297
298 //-----------------------------------------------------------------------
299 /**
300 * Constructor.
301 *
302 * @param year the year to represent, validated from MIN_YEAR to MAX_YEAR
303 * @param month the month-of-year to represent, validated from 1 (January) to 12 (December)
304 */
305 private YearMonth(int year, int month) {
306 this.year = year;
307 this.month = month;
308 }
309
310 /**
311 * Returns a copy of this year-month with the new year and month, checking
312 * to see if a new object is in fact required.
313 *
314 * @param newYear the year to represent, validated from MIN_YEAR to MAX_YEAR
315 * @param newMonth the month-of-year to represent, validated not null
316 * @return the year-month, not null
317 */
318 private YearMonth with(int newYear, int newMonth) {
319 if (year == newYear && month == newMonth) {
320 return this;
321 }
322 return new YearMonth(newYear, newMonth);
323 }
324
325 //-----------------------------------------------------------------------
326 /**
327 * Checks if the specified field is supported.
328 * <p>
329 * This checks if this year-month can be queried for the specified field.
330 * If false, then calling the {@link #range(TemporalField) range},
331 * {@link #get(TemporalField) get} and {@link #with(TemporalField, long)}
332 * methods will throw an exception.
333 * <p>
334 * If the field is a {@link ChronoField} then the query is implemented here.
335 * The supported fields are:
336 * <ul>
337 * <li>{@code MONTH_OF_YEAR}
338 * <li>{@code PROLEPTIC_MONTH}
339 * <li>{@code YEAR_OF_ERA}
340 * <li>{@code YEAR}
341 * <li>{@code ERA}
342 * </ul>
343 * All other {@code ChronoField} instances will return false.
344 * <p>
345 * If the field is not a {@code ChronoField}, then the result of this method
346 * is obtained by invoking {@code TemporalField.isSupportedBy(TemporalAccessor)}
347 * passing {@code this} as the argument.
348 * Whether the field is supported is determined by the field.
349 *
350 * @param field the field to check, null returns false
351 * @return true if the field is supported on this year-month, false if not
352 */
353 @Override
354 public boolean isSupported(TemporalField field) {
355 if (field instanceof ChronoField) {
356 return field == YEAR || field == MONTH_OF_YEAR ||
357 field == PROLEPTIC_MONTH || field == YEAR_OF_ERA || field == ERA;
358 }
359 return field != null && field.isSupportedBy(this);
360 }
361
362 /**
363 * Checks if the specified unit is supported.
364 * <p>
365 * This checks if the specified unit can be added to, or subtracted from, this year-month.
366 * If false, then calling the {@link #plus(long, TemporalUnit)} and
367 * {@link #minus(long, TemporalUnit) minus} methods will throw an exception.
368 * <p>
369 * If the unit is a {@link ChronoUnit} then the query is implemented here.
370 * The supported units are:
371 * <ul>
372 * <li>{@code MONTHS}
373 * <li>{@code YEARS}
374 * <li>{@code DECADES}
375 * <li>{@code CENTURIES}
376 * <li>{@code MILLENNIA}
377 * <li>{@code ERAS}
378 * </ul>
379 * All other {@code ChronoUnit} instances will return false.
380 * <p>
381 * If the unit is not a {@code ChronoUnit}, then the result of this method
382 * is obtained by invoking {@code TemporalUnit.isSupportedBy(Temporal)}
383 * passing {@code this} as the argument.
384 * Whether the unit is supported is determined by the unit.
385 *
386 * @param unit the unit to check, null returns false
387 * @return true if the unit can be added/subtracted, false if not
388 */
389 @Override
390 public boolean isSupported(TemporalUnit unit) {
391 if (unit instanceof ChronoUnit) {
392 return unit == MONTHS || unit == YEARS || unit == DECADES || unit == CENTURIES || unit == MILLENNIA || unit == ERAS;
393 }
394 return unit != null && unit.isSupportedBy(this);
395 }
396
397 //-----------------------------------------------------------------------
398 /**
399 * Gets the range of valid values for the specified field.
400 * <p>
401 * The range object expresses the minimum and maximum valid values for a field.
402 * This year-month is used to enhance the accuracy of the returned range.
403 * If it is not possible to return the range, because the field is not supported
404 * or for some other reason, an exception is thrown.
405 * <p>
406 * If the field is a {@link ChronoField} then the query is implemented here.
407 * The {@link #isSupported(TemporalField) supported fields} will return
408 * appropriate range instances.
409 * All other {@code ChronoField} instances will throw an {@code UnsupportedTemporalTypeException}.
410 * <p>
411 * If the field is not a {@code ChronoField}, then the result of this method
412 * is obtained by invoking {@code TemporalField.rangeRefinedBy(TemporalAccessor)}
413 * passing {@code this} as the argument.
414 * Whether the range can be obtained is determined by the field.
415 *
416 * @param field the field to query the range for, not null
417 * @return the range of valid values for the field, not null
418 * @throws DateTimeException if the range for the field cannot be obtained
419 * @throws UnsupportedTemporalTypeException if the field is not supported
420 */
421 @Override
422 public ValueRange range(TemporalField field) {
423 if (field == YEAR_OF_ERA) {
424 return (getYear() <= 0 ? ValueRange.of(1, Year.MAX_VALUE + 1) : ValueRange.of(1, Year.MAX_VALUE));
425 }
426 return Temporal.super.range(field);
427 }
428
429 /**
430 * Gets the value of the specified field from this year-month as an {@code int}.
431 * <p>
432 * This queries this year-month for the value of the specified field.
433 * The returned value will always be within the valid range of values for the field.
434 * If it is not possible to return the value, because the field is not supported
435 * or for some other reason, an exception is thrown.
436 * <p>
437 * If the field is a {@link ChronoField} then the query is implemented here.
438 * The {@link #isSupported(TemporalField) supported fields} will return valid
439 * values based on this year-month, except {@code PROLEPTIC_MONTH} which is too
440 * large to fit in an {@code int} and throw a {@code DateTimeException}.
441 * All other {@code ChronoField} instances will throw an {@code UnsupportedTemporalTypeException}.
442 * <p>
443 * If the field is not a {@code ChronoField}, then the result of this method
444 * is obtained by invoking {@code TemporalField.getFrom(TemporalAccessor)}
445 * passing {@code this} as the argument. Whether the value can be obtained,
446 * and what the value represents, is determined by the field.
447 *
448 * @param field the field to get, not null
449 * @return the value for the field
450 * @throws DateTimeException if a value for the field cannot be obtained or
451 * the value is outside the range of valid values for the field
452 * @throws UnsupportedTemporalTypeException if the field is not supported or
453 * the range of values exceeds an {@code int}
454 * @throws ArithmeticException if numeric overflow occurs
455 */
456 @Override // override for Javadoc
457 public int get(TemporalField field) {
458 return range(field).checkValidIntValue(getLong(field), field);
459 }
460
461 /**
462 * Gets the value of the specified field from this year-month as a {@code long}.
463 * <p>
464 * This queries this year-month for the value of the specified field.
465 * If it is not possible to return the value, because the field is not supported
466 * or for some other reason, an exception is thrown.
467 * <p>
468 * If the field is a {@link ChronoField} then the query is implemented here.
469 * The {@link #isSupported(TemporalField) supported fields} will return valid
470 * values based on this year-month.
471 * All other {@code ChronoField} instances will throw an {@code UnsupportedTemporalTypeException}.
472 * <p>
473 * If the field is not a {@code ChronoField}, then the result of this method
474 * is obtained by invoking {@code TemporalField.getFrom(TemporalAccessor)}
475 * passing {@code this} as the argument. Whether the value can be obtained,
476 * and what the value represents, is determined by the field.
477 *
478 * @param field the field to get, not null
479 * @return the value for the field
480 * @throws DateTimeException if a value for the field cannot be obtained
481 * @throws UnsupportedTemporalTypeException if the field is not supported
482 * @throws ArithmeticException if numeric overflow occurs
483 */
484 @Override
485 public long getLong(TemporalField field) {
486 if (field instanceof ChronoField) {
487 switch ((ChronoField) field) {
488 case MONTH_OF_YEAR: return month;
489 case PROLEPTIC_MONTH: return getProlepticMonth();
490 case YEAR_OF_ERA: return (year < 1 ? 1 - year : year);
491 case YEAR: return year;
492 case ERA: return (year < 1 ? 0 : 1);
493 }
494 throw new UnsupportedTemporalTypeException("Unsupported field: " + field);
495 }
496 return field.getFrom(this);
497 }
498
499 private long getProlepticMonth() {
500 return (year * 12L + month - 1);
501 }
502
503 //-----------------------------------------------------------------------
504 /**
505 * Gets the year field.
506 * <p>
507 * This method returns the primitive {@code int} value for the year.
508 * <p>
509 * The year returned by this method is proleptic as per {@code get(YEAR)}.
510 *
511 * @return the year, from MIN_YEAR to MAX_YEAR
512 */
513 public int getYear() {
514 return year;
515 }
516
517 /**
518 * Gets the month-of-year field from 1 to 12.
519 * <p>
520 * This method returns the month as an {@code int} from 1 to 12.
521 * Application code is frequently clearer if the enum {@link Month}
522 * is used by calling {@link #getMonth()}.
523 *
524 * @return the month-of-year, from 1 to 12
525 * @see #getMonth()
526 */
527 public int getMonthValue() {
528 return month;
529 }
530
531 /**
532 * Gets the month-of-year field using the {@code Month} enum.
533 * <p>
534 * This method returns the enum {@link Month} for the month.
535 * This avoids confusion as to what {@code int} values mean.
536 * If you need access to the primitive {@code int} value then the enum
537 * provides the {@link Month#getValue() int value}.
538 *
539 * @return the month-of-year, not null
540 * @see #getMonthValue()
541 */
542 public Month getMonth() {
543 return Month.of(month);
544 }
545
546 //-----------------------------------------------------------------------
547 /**
548 * Checks if the year is a leap year, according to the ISO proleptic
549 * calendar system rules.
550 * <p>
551 * This method applies the current rules for leap years across the whole time-line.
552 * In general, a year is a leap year if it is divisible by four without
553 * remainder. However, years divisible by 100, are not leap years, with
554 * the exception of years divisible by 400 which are.
555 * <p>
556 * For example, 1904 is a leap year it is divisible by 4.
557 * 1900 was not a leap year as it is divisible by 100, however 2000 was a
558 * leap year as it is divisible by 400.
559 * <p>
560 * The calculation is proleptic - applying the same rules into the far future and far past.
561 * This is historically inaccurate, but is correct for the ISO-8601 standard.
562 *
563 * @return true if the year is leap, false otherwise
564 */
565 public boolean isLeapYear() {
566 return IsoChronology.INSTANCE.isLeapYear(year);
567 }
568
569 /**
570 * Checks if the day-of-month is valid for this year-month.
571 * <p>
572 * This method checks whether this year and month and the input day form
573 * a valid date.
574 *
575 * @param dayOfMonth the day-of-month to validate, from 1 to 31, invalid value returns false
576 * @return true if the day is valid for this year-month
577 */
578 public boolean isValidDay(int dayOfMonth) {
579 return dayOfMonth >= 1 && dayOfMonth <= lengthOfMonth();
580 }
581
582 /**
583 * Returns the length of the month, taking account of the year.
584 * <p>
585 * This returns the length of the month in days.
586 * For example, a date in January would return 31.
587 *
588 * @return the length of the month in days, from 28 to 31
589 */
590 public int lengthOfMonth() {
591 return getMonth().length(isLeapYear());
592 }
593
594 /**
595 * Returns the length of the year.
596 * <p>
597 * This returns the length of the year in days, either 365 or 366.
598 *
599 * @return 366 if the year is leap, 365 otherwise
600 */
601 public int lengthOfYear() {
602 return (isLeapYear() ? 366 : 365);
603 }
604
605 //-----------------------------------------------------------------------
606 /**
607 * Returns an adjusted copy of this year-month.
608 * <p>
609 * This returns a {@code YearMonth}, based on this one, with the year-month adjusted.
610 * The adjustment takes place using the specified adjuster strategy object.
611 * Read the documentation of the adjuster to understand what adjustment will be made.
612 * <p>
613 * A simple adjuster might simply set the one of the fields, such as the year field.
614 * A more complex adjuster might set the year-month to the next month that
615 * Halley's comet will pass the Earth.
616 * <p>
617 * The result of this method is obtained by invoking the
618 * {@link TemporalAdjuster#adjustInto(Temporal)} method on the
619 * specified adjuster passing {@code this} as the argument.
620 * <p>
621 * This instance is immutable and unaffected by this method call.
622 *
623 * @param adjuster the adjuster to use, not null
624 * @return a {@code YearMonth} based on {@code this} with the adjustment made, not null
625 * @throws DateTimeException if the adjustment cannot be made
626 * @throws ArithmeticException if numeric overflow occurs
627 */
628 @Override
629 public YearMonth with(TemporalAdjuster adjuster) {
630 return (YearMonth) adjuster.adjustInto(this);
631 }
632
633 /**
634 * Returns a copy of this year-month with the specified field set to a new value.
635 * <p>
636 * This returns a {@code YearMonth}, based on this one, with the value
637 * for the specified field changed.
638 * This can be used to change any supported field, such as the year or month.
639 * If it is not possible to set the value, because the field is not supported or for
640 * some other reason, an exception is thrown.
641 * <p>
642 * If the field is a {@link ChronoField} then the adjustment is implemented here.
643 * The supported fields behave as follows:
644 * <ul>
645 * <li>{@code MONTH_OF_YEAR} -
646 * Returns a {@code YearMonth} with the specified month-of-year.
647 * The year will be unchanged.
648 * <li>{@code PROLEPTIC_MONTH} -
649 * Returns a {@code YearMonth} with the specified proleptic-month.
650 * This completely replaces the year and month of this object.
651 * <li>{@code YEAR_OF_ERA} -
652 * Returns a {@code YearMonth} with the specified year-of-era
653 * The month and era will be unchanged.
654 * <li>{@code YEAR} -
655 * Returns a {@code YearMonth} with the specified year.
656 * The month will be unchanged.
657 * <li>{@code ERA} -
658 * Returns a {@code YearMonth} with the specified era.
659 * The month and year-of-era will be unchanged.
660 * </ul>
661 * <p>
662 * In all cases, if the new value is outside the valid range of values for the field
663 * then a {@code DateTimeException} will be thrown.
664 * <p>
665 * All other {@code ChronoField} instances will throw an {@code UnsupportedTemporalTypeException}.
666 * <p>
667 * If the field is not a {@code ChronoField}, then the result of this method
668 * is obtained by invoking {@code TemporalField.adjustInto(Temporal, long)}
669 * passing {@code this} as the argument. In this case, the field determines
670 * whether and how to adjust the instant.
671 * <p>
672 * This instance is immutable and unaffected by this method call.
673 *
674 * @param field the field to set in the result, not null
675 * @param newValue the new value of the field in the result
676 * @return a {@code YearMonth} based on {@code this} with the specified field set, not null
677 * @throws DateTimeException if the field cannot be set
678 * @throws UnsupportedTemporalTypeException if the field is not supported
679 * @throws ArithmeticException if numeric overflow occurs
680 */
681 @Override
682 public YearMonth with(TemporalField field, long newValue) {
683 if (field instanceof ChronoField) {
684 ChronoField f = (ChronoField) field;
685 f.checkValidValue(newValue);
686 switch (f) {
687 case MONTH_OF_YEAR: return withMonth((int) newValue);
688 case PROLEPTIC_MONTH: return plusMonths(newValue - getProlepticMonth());
689 case YEAR_OF_ERA: return withYear((int) (year < 1 ? 1 - newValue : newValue));
690 case YEAR: return withYear((int) newValue);
691 case ERA: return (getLong(ERA) == newValue ? this : withYear(1 - year));
692 }
693 throw new UnsupportedTemporalTypeException("Unsupported field: " + field);
694 }
695 return field.adjustInto(this, newValue);
696 }
697
698 //-----------------------------------------------------------------------
699 /**
700 * Returns a copy of this {@code YearMonth} with the year altered.
701 * <p>
702 * This instance is immutable and unaffected by this method call.
703 *
704 * @param year the year to set in the returned year-month, from MIN_YEAR to MAX_YEAR
705 * @return a {@code YearMonth} based on this year-month with the requested year, not null
706 * @throws DateTimeException if the year value is invalid
707 */
708 public YearMonth withYear(int year) {
709 YEAR.checkValidValue(year);
710 return with(year, month);
711 }
712
713 /**
714 * Returns a copy of this {@code YearMonth} with the month-of-year altered.
715 * <p>
716 * This instance is immutable and unaffected by this method call.
717 *
718 * @param month the month-of-year to set in the returned year-month, from 1 (January) to 12 (December)
719 * @return a {@code YearMonth} based on this year-month with the requested month, not null
720 * @throws DateTimeException if the month-of-year value is invalid
721 */
722 public YearMonth withMonth(int month) {
723 MONTH_OF_YEAR.checkValidValue(month);
724 return with(year, month);
725 }
726
727 //-----------------------------------------------------------------------
728 /**
729 * Returns a copy of this year-month with the specified amount added.
730 * <p>
731 * This returns a {@code YearMonth}, based on this one, with the specified amount added.
732 * The amount is typically {@link Period} but may be any other type implementing
733 * the {@link TemporalAmount} interface.
734 * <p>
735 * The calculation is delegated to the amount object by calling
736 * {@link TemporalAmount#addTo(Temporal)}. The amount implementation is free
737 * to implement the addition in any way it wishes, however it typically
738 * calls back to {@link #plus(long, TemporalUnit)}. Consult the documentation
739 * of the amount implementation to determine if it can be successfully added.
740 * <p>
741 * This instance is immutable and unaffected by this method call.
742 *
743 * @param amountToAdd the amount to add, not null
744 * @return a {@code YearMonth} based on this year-month with the addition made, not null
745 * @throws DateTimeException if the addition cannot be made
746 * @throws ArithmeticException if numeric overflow occurs
747 */
748 @Override
749 public YearMonth plus(TemporalAmount amountToAdd) {
750 return (YearMonth) amountToAdd.addTo(this);
751 }
752
753 /**
754 * Returns a copy of this year-month with the specified amount added.
755 * <p>
756 * This returns a {@code YearMonth}, based on this one, with the amount
757 * in terms of the unit added. If it is not possible to add the amount, because the
758 * unit is not supported or for some other reason, an exception is thrown.
759 * <p>
760 * If the field is a {@link ChronoUnit} then the addition is implemented here.
761 * The supported fields behave as follows:
762 * <ul>
763 * <li>{@code MONTHS} -
764 * Returns a {@code YearMonth} with the specified number of months added.
765 * This is equivalent to {@link #plusMonths(long)}.
766 * <li>{@code YEARS} -
767 * Returns a {@code YearMonth} with the specified number of years added.
768 * This is equivalent to {@link #plusYears(long)}.
769 * <li>{@code DECADES} -
770 * Returns a {@code YearMonth} with the specified number of decades added.
771 * This is equivalent to calling {@link #plusYears(long)} with the amount
772 * multiplied by 10.
773 * <li>{@code CENTURIES} -
774 * Returns a {@code YearMonth} with the specified number of centuries added.
775 * This is equivalent to calling {@link #plusYears(long)} with the amount
776 * multiplied by 100.
777 * <li>{@code MILLENNIA} -
778 * Returns a {@code YearMonth} with the specified number of millennia added.
779 * This is equivalent to calling {@link #plusYears(long)} with the amount
780 * multiplied by 1,000.
781 * <li>{@code ERAS} -
782 * Returns a {@code YearMonth} with the specified number of eras added.
783 * Only two eras are supported so the amount must be one, zero or minus one.
784 * If the amount is non-zero then the year is changed such that the year-of-era
785 * is unchanged.
786 * </ul>
787 * <p>
788 * All other {@code ChronoUnit} instances will throw an {@code UnsupportedTemporalTypeException}.
789 * <p>
790 * If the field is not a {@code ChronoUnit}, then the result of this method
791 * is obtained by invoking {@code TemporalUnit.addTo(Temporal, long)}
792 * passing {@code this} as the argument. In this case, the unit determines
793 * whether and how to perform the addition.
794 * <p>
795 * This instance is immutable and unaffected by this method call.
796 *
797 * @param amountToAdd the amount of the unit to add to the result, may be negative
798 * @param unit the unit of the amount to add, not null
799 * @return a {@code YearMonth} based on this year-month with the specified amount added, not null
800 * @throws DateTimeException if the addition cannot be made
801 * @throws UnsupportedTemporalTypeException if the unit is not supported
802 * @throws ArithmeticException if numeric overflow occurs
803 */
804 @Override
805 public YearMonth plus(long amountToAdd, TemporalUnit unit) {
806 if (unit instanceof ChronoUnit) {
807 switch ((ChronoUnit) unit) {
808 case MONTHS: return plusMonths(amountToAdd);
809 case YEARS: return plusYears(amountToAdd);
810 case DECADES: return plusYears(Math.multiplyExact(amountToAdd, 10));
811 case CENTURIES: return plusYears(Math.multiplyExact(amountToAdd, 100));
812 case MILLENNIA: return plusYears(Math.multiplyExact(amountToAdd, 1000));
813 case ERAS: return with(ERA, Math.addExact(getLong(ERA), amountToAdd));
814 }
815 throw new UnsupportedTemporalTypeException("Unsupported unit: " + unit);
816 }
817 return unit.addTo(this, amountToAdd);
818 }
819
820 /**
821 * Returns a copy of this {@code YearMonth} with the specified number of years added.
822 * <p>
823 * This instance is immutable and unaffected by this method call.
824 *
825 * @param yearsToAdd the years to add, may be negative
826 * @return a {@code YearMonth} based on this year-month with the years added, not null
827 * @throws DateTimeException if the result exceeds the supported range
828 */
829 public YearMonth plusYears(long yearsToAdd) {
830 if (yearsToAdd == 0) {
831 return this;
832 }
833 int newYear = YEAR.checkValidIntValue(year + yearsToAdd); // safe overflow
834 return with(newYear, month);
835 }
836
837 /**
838 * Returns a copy of this {@code YearMonth} with the specified number of months added.
839 * <p>
840 * This instance is immutable and unaffected by this method call.
841 *
842 * @param monthsToAdd the months to add, may be negative
843 * @return a {@code YearMonth} based on this year-month with the months added, not null
844 * @throws DateTimeException if the result exceeds the supported range
845 */
846 public YearMonth plusMonths(long monthsToAdd) {
847 if (monthsToAdd == 0) {
848 return this;
849 }
850 long monthCount = year * 12L + (month - 1);
851 long calcMonths = monthCount + monthsToAdd; // safe overflow
852 int newYear = YEAR.checkValidIntValue(Math.floorDiv(calcMonths, 12));
853 int newMonth = (int)Math.floorMod(calcMonths, 12) + 1;
854 return with(newYear, newMonth);
855 }
856
857 //-----------------------------------------------------------------------
858 /**
859 * Returns a copy of this year-month with the specified amount subtracted.
860 * <p>
861 * This returns a {@code YearMonth}, based on this one, with the specified amount subtracted.
862 * The amount is typically {@link Period} but may be any other type implementing
863 * the {@link TemporalAmount} interface.
864 * <p>
865 * The calculation is delegated to the amount object by calling
866 * {@link TemporalAmount#subtractFrom(Temporal)}. The amount implementation is free
867 * to implement the subtraction in any way it wishes, however it typically
868 * calls back to {@link #minus(long, TemporalUnit)}. Consult the documentation
869 * of the amount implementation to determine if it can be successfully subtracted.
870 * <p>
871 * This instance is immutable and unaffected by this method call.
872 *
873 * @param amountToSubtract the amount to subtract, not null
874 * @return a {@code YearMonth} based on this year-month with the subtraction made, not null
875 * @throws DateTimeException if the subtraction cannot be made
876 * @throws ArithmeticException if numeric overflow occurs
877 */
878 @Override
879 public YearMonth minus(TemporalAmount amountToSubtract) {
880 return (YearMonth) amountToSubtract.subtractFrom(this);
881 }
882
883 /**
884 * Returns a copy of this year-month with the specified amount subtracted.
885 * <p>
886 * This returns a {@code YearMonth}, based on this one, with the amount
887 * in terms of the unit subtracted. If it is not possible to subtract the amount,
888 * because the unit is not supported or for some other reason, an exception is thrown.
889 * <p>
890 * This method is equivalent to {@link #plus(long, TemporalUnit)} with the amount negated.
891 * See that method for a full description of how addition, and thus subtraction, works.
892 * <p>
893 * This instance is immutable and unaffected by this method call.
894 *
895 * @param amountToSubtract the amount of the unit to subtract from the result, may be negative
896 * @param unit the unit of the amount to subtract, not null
897 * @return a {@code YearMonth} based on this year-month with the specified amount subtracted, not null
898 * @throws DateTimeException if the subtraction cannot be made
899 * @throws UnsupportedTemporalTypeException if the unit is not supported
900 * @throws ArithmeticException if numeric overflow occurs
901 */
902 @Override
903 public YearMonth minus(long amountToSubtract, TemporalUnit unit) {
904 return (amountToSubtract == Long.MIN_VALUE ? plus(Long.MAX_VALUE, unit).plus(1, unit) : plus(-amountToSubtract, unit));
905 }
906
907 /**
908 * Returns a copy of this {@code YearMonth} with the specified number of years subtracted.
909 * <p>
910 * This instance is immutable and unaffected by this method call.
911 *
912 * @param yearsToSubtract the years to subtract, may be negative
913 * @return a {@code YearMonth} based on this year-month with the years subtracted, not null
914 * @throws DateTimeException if the result exceeds the supported range
915 */
916 public YearMonth minusYears(long yearsToSubtract) {
917 return (yearsToSubtract == Long.MIN_VALUE ? plusYears(Long.MAX_VALUE).plusYears(1) : plusYears(-yearsToSubtract));
918 }
919
920 /**
921 * Returns a copy of this {@code YearMonth} with the specified number of months subtracted.
922 * <p>
923 * This instance is immutable and unaffected by this method call.
924 *
925 * @param monthsToSubtract the months to subtract, may be negative
926 * @return a {@code YearMonth} based on this year-month with the months subtracted, not null
927 * @throws DateTimeException if the result exceeds the supported range
928 */
929 public YearMonth minusMonths(long monthsToSubtract) {
930 return (monthsToSubtract == Long.MIN_VALUE ? plusMonths(Long.MAX_VALUE).plusMonths(1) : plusMonths(-monthsToSubtract));
931 }
932
933 //-----------------------------------------------------------------------
934 /**
935 * Queries this year-month using the specified query.
936 * <p>
937 * This queries this year-month using the specified query strategy object.
938 * The {@code TemporalQuery} object defines the logic to be used to
939 * obtain the result. Read the documentation of the query to understand
940 * what the result of this method will be.
941 * <p>
942 * The result of this method is obtained by invoking the
943 * {@link TemporalQuery#queryFrom(TemporalAccessor)} method on the
944 * specified query passing {@code this} as the argument.
945 *
946 * @param <R> the type of the result
947 * @param query the query to invoke, not null
948 * @return the query result, null may be returned (defined by the query)
949 * @throws DateTimeException if unable to query (defined by the query)
950 * @throws ArithmeticException if numeric overflow occurs (defined by the query)
951 */
952 @SuppressWarnings("unchecked")
953 @Override
954 public <R> R query(TemporalQuery<R> query) {
955 if (query == TemporalQueries.chronology()) {
956 return (R) IsoChronology.INSTANCE;
957 } else if (query == TemporalQueries.precision()) {
958 return (R) MONTHS;
959 }
960 return Temporal.super.query(query);
961 }
962
963 /**
964 * Adjusts the specified temporal object to have this year-month.
965 * <p>
966 * This returns a temporal object of the same observable type as the input
967 * with the year and month changed to be the same as this.
968 * <p>
969 * The adjustment is equivalent to using {@link Temporal#with(TemporalField, long)}
970 * passing {@link ChronoField#PROLEPTIC_MONTH} as the field.
971 * If the specified temporal object does not use the ISO calendar system then
972 * a {@code DateTimeException} is thrown.
973 * <p>
974 * In most cases, it is clearer to reverse the calling pattern by using
975 * {@link Temporal#with(TemporalAdjuster)}:
976 * <pre>
977 * // these two lines are equivalent, but the second approach is recommended
978 * temporal = thisYearMonth.adjustInto(temporal);
979 * temporal = temporal.with(thisYearMonth);
980 * </pre>
981 * <p>
982 * This instance is immutable and unaffected by this method call.
983 *
984 * @param temporal the target object to be adjusted, not null
985 * @return the adjusted object, not null
986 * @throws DateTimeException if unable to make the adjustment
987 * @throws ArithmeticException if numeric overflow occurs
988 */
989 @Override
990 public Temporal adjustInto(Temporal temporal) {
991 if (Chronology.from(temporal).equals(IsoChronology.INSTANCE) == false) {
992 throw new DateTimeException("Adjustment only supported on ISO date-time");
993 }
994 return temporal.with(PROLEPTIC_MONTH, getProlepticMonth());
995 }
996
997 /**
998 * Calculates the amount of time until another year-month in terms of the specified unit.
999 * <p>
1000 * This calculates the amount of time between two {@code YearMonth}
1001 * objects in terms of a single {@code TemporalUnit}.
1002 * The start and end points are {@code this} and the specified year-month.
1003 * The result will be negative if the end is before the start.
1004 * The {@code Temporal} passed to this method is converted to a
1005 * {@code YearMonth} using {@link #from(TemporalAccessor)}.
1006 * For example, the amount in years between two year-months can be calculated
1007 * using {@code startYearMonth.until(endYearMonth, YEARS)}.
1008 * <p>
1009 * The calculation returns a whole number, representing the number of
1010 * complete units between the two year-months.
1011 * For example, the amount in decades between 2012-06 and 2032-05
1012 * will only be one decade as it is one month short of two decades.
1013 * <p>
1014 * There are two equivalent ways of using this method.
1015 * The first is to invoke this method.
1016 * The second is to use {@link TemporalUnit#between(Temporal, Temporal)}:
1017 * <pre>
1018 * // these two lines are equivalent
1019 * amount = start.until(end, MONTHS);
1020 * amount = MONTHS.between(start, end);
1021 * </pre>
1022 * The choice should be made based on which makes the code more readable.
1023 * <p>
1024 * The calculation is implemented in this method for {@link ChronoUnit}.
1025 * The units {@code MONTHS}, {@code YEARS}, {@code DECADES},
1026 * {@code CENTURIES}, {@code MILLENNIA} and {@code ERAS} are supported.
1027 * Other {@code ChronoUnit} values will throw an exception.
1028 * <p>
1029 * If the unit is not a {@code ChronoUnit}, then the result of this method
1030 * is obtained by invoking {@code TemporalUnit.between(Temporal, Temporal)}
1031 * passing {@code this} as the first argument and the converted input temporal
1032 * as the second argument.
1033 * <p>
1034 * This instance is immutable and unaffected by this method call.
1035 *
1036 * @param endExclusive the end date, exclusive, which is converted to a {@code YearMonth}, not null
1037 * @param unit the unit to measure the amount in, not null
1038 * @return the amount of time between this year-month and the end year-month
1039 * @throws DateTimeException if the amount cannot be calculated, or the end
1040 * temporal cannot be converted to a {@code YearMonth}
1041 * @throws UnsupportedTemporalTypeException if the unit is not supported
1042 * @throws ArithmeticException if numeric overflow occurs
1043 */
1044 @Override
1045 public long until(Temporal endExclusive, TemporalUnit unit) {
1046 YearMonth end = YearMonth.from(endExclusive);
1047 if (unit instanceof ChronoUnit) {
1048 long monthsUntil = end.getProlepticMonth() - getProlepticMonth(); // no overflow
1049 switch ((ChronoUnit) unit) {
1050 case MONTHS: return monthsUntil;
1051 case YEARS: return monthsUntil / 12;
1052 case DECADES: return monthsUntil / 120;
1053 case CENTURIES: return monthsUntil / 1200;
1054 case MILLENNIA: return monthsUntil / 12000;
1055 case ERAS: return end.getLong(ERA) - getLong(ERA);
1056 }
1057 throw new UnsupportedTemporalTypeException("Unsupported unit: " + unit);
1058 }
1059 return unit.between(this, end);
1060 }
1061
1062 /**
1063 * Formats this year-month using the specified formatter.
1064 * <p>
1065 * This year-month will be passed to the formatter to produce a string.
1066 *
1067 * @param formatter the formatter to use, not null
1068 * @return the formatted year-month string, not null
1069 * @throws DateTimeException if an error occurs during printing
1070 */
1071 public String format(DateTimeFormatter formatter) {
1072 Objects.requireNonNull(formatter, "formatter");
1073 return formatter.format(this);
1074 }
1075
1076 //-----------------------------------------------------------------------
1077 /**
1078 * Combines this year-month with a day-of-month to create a {@code LocalDate}.
1079 * <p>
1080 * This returns a {@code LocalDate} formed from this year-month and the specified day-of-month.
1081 * <p>
1082 * The day-of-month value must be valid for the year-month.
1083 * <p>
1084 * This method can be used as part of a chain to produce a date:
1085 * <pre>
1086 * LocalDate date = year.atMonth(month).atDay(day);
1087 * </pre>
1088 *
1089 * @param dayOfMonth the day-of-month to use, from 1 to 31
1090 * @return the date formed from this year-month and the specified day, not null
1091 * @throws DateTimeException if the day is invalid for the year-month
1092 * @see #isValidDay(int)
1093 */
1094 public LocalDate atDay(int dayOfMonth) {
1095 return LocalDate.of(year, month, dayOfMonth);
1096 }
1097
1098 /**
1099 * Returns a {@code LocalDate} at the end of the month.
1100 * <p>
1101 * This returns a {@code LocalDate} based on this year-month.
1102 * The day-of-month is set to the last valid day of the month, taking
1103 * into account leap years.
1104 * <p>
1105 * This method can be used as part of a chain to produce a date:
1106 * <pre>
1107 * LocalDate date = year.atMonth(month).atEndOfMonth();
1108 * </pre>
1109 *
1110 * @return the last valid date of this year-month, not null
1111 */
1112 public LocalDate atEndOfMonth() {
1113 return LocalDate.of(year, month, lengthOfMonth());
1114 }
1115
1116 //-----------------------------------------------------------------------
1117 /**
1118 * Compares this year-month to another year-month.
1119 * <p>
1120 * The comparison is based first on the value of the year, then on the value of the month.
1121 * It is "consistent with equals", as defined by {@link Comparable}.
1122 *
1123 * @param other the other year-month to compare to, not null
1124 * @return the comparator value, negative if less, positive if greater
1125 */
1126 @Override
1127 public int compareTo(YearMonth other) {
1128 int cmp = (year - other.year);
1129 if (cmp == 0) {
1130 cmp = (month - other.month);
1131 }
1132 return cmp;
1133 }
1134
1135 /**
1136 * Checks if this year-month is after the specified year-month.
1137 *
1138 * @param other the other year-month to compare to, not null
1139 * @return true if this is after the specified year-month
1140 */
1141 public boolean isAfter(YearMonth other) {
1142 return compareTo(other) > 0;
1143 }
1144
1145 /**
1146 * Checks if this year-month is before the specified year-month.
1147 *
1148 * @param other the other year-month to compare to, not null
1149 * @return true if this point is before the specified year-month
1150 */
1151 public boolean isBefore(YearMonth other) {
1152 return compareTo(other) < 0;
1153 }
1154
1155 //-----------------------------------------------------------------------
1156 /**
1157 * Checks if this year-month is equal to another year-month.
1158 * <p>
1159 * The comparison is based on the time-line position of the year-months.
1160 *
1161 * @param obj the object to check, null returns false
1162 * @return true if this is equal to the other year-month
1163 */
1164 @Override
1165 public boolean equals(Object obj) {
1166 if (this == obj) {
1167 return true;
1168 }
1169 if (obj instanceof YearMonth) {
1170 YearMonth other = (YearMonth) obj;
1171 return year == other.year && month == other.month;
1172 }
1173 return false;
1174 }
1175
1176 /**
1177 * A hash code for this year-month.
1178 *
1179 * @return a suitable hash code
1180 */
1181 @Override
1182 public int hashCode() {
1183 return year ^ (month << 27);
1184 }
1185
1186 //-----------------------------------------------------------------------
1187 /**
1188 * Outputs this year-month as a {@code String}, such as {@code 2007-12}.
1189 * <p>
1190 * The output will be in the format {@code uuuu-MM}:
1191 *
1192 * @return a string representation of this year-month, not null
1193 */
1194 @Override
1195 public String toString() {
1196 int absYear = Math.abs(year);
1197 StringBuilder buf = new StringBuilder(9);
1198 if (absYear < 1000) {
1199 if (year < 0) {
1200 buf.append(year - 10000).deleteCharAt(1);
1201 } else {
1202 buf.append(year + 10000).deleteCharAt(0);
1203 }
1204 } else {
1205 buf.append(year);
1206 }
1207 return buf.append(month < 10 ? "-0" : "-")
1208 .append(month)
1209 .toString();
1210 }
1211
1212 //-----------------------------------------------------------------------
1213 /**
1214 * Writes the object using a
1215 * <a href="../../serialized-form.html#java.time.Ser">dedicated serialized form</a>.
1216 * @serialData
1217 * <pre>
1218 * out.writeByte(12); // identifies a YearMonth
1219 * out.writeInt(year);
1220 * out.writeByte(month);
1221 * </pre>
1222 *
1223 * @return the instance of {@code Ser}, not null
1224 */
1225 private Object writeReplace() {
1226 return new Ser(Ser.YEAR_MONTH_TYPE, this);
1227 }
1228
1229 /**
1230 * Defend against malicious streams.
1231 *
1232 * @param s the stream to read
1233 * @throws InvalidObjectException always
1234 */
1235 private void readObject(ObjectInputStream s) throws InvalidObjectException {
1236 throw new InvalidObjectException("Deserialization via serialization delegate");
1237 }
1238
1239 void writeExternal(DataOutput out) throws IOException {
1240 out.writeInt(year);
1241 out.writeByte(month);
1242 }
1243
1244 static YearMonth readExternal(DataInput in) throws IOException {
1245 int year = in.readInt();
1246 byte month = in.readByte();
1247 return YearMonth.of(year, month);
1248 }
1249
1250 }