1 /*
   2  * Copyright (c) 2012, 2018, 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
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   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) 2008-2012, 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.ChronoUnit.DAYS;
  65 import static java.time.temporal.ChronoUnit.MONTHS;
  66 import static java.time.temporal.ChronoUnit.YEARS;
  67 
  68 import java.io.DataInput;
  69 import java.io.DataOutput;
  70 import java.io.IOException;
  71 import java.io.InvalidObjectException;
  72 import java.io.ObjectInputStream;
  73 import java.io.Serializable;
  74 import java.time.chrono.ChronoLocalDate;
  75 import java.time.chrono.ChronoPeriod;
  76 import java.time.chrono.Chronology;
  77 import java.time.chrono.IsoChronology;
  78 import java.time.format.DateTimeParseException;
  79 import java.time.temporal.ChronoUnit;
  80 import java.time.temporal.Temporal;
  81 import java.time.temporal.TemporalAccessor;
  82 import java.time.temporal.TemporalAmount;
  83 import java.time.temporal.TemporalQueries;
  84 import java.time.temporal.TemporalUnit;
  85 import java.time.temporal.UnsupportedTemporalTypeException;
  86 import java.util.List;
  87 import java.util.Objects;
  88 import java.util.regex.Matcher;
  89 import java.util.regex.Pattern;
  90 
  91 /**
  92  * A date-based amount of time in the ISO-8601 calendar system,
  93  * such as '2 years, 3 months and 4 days'.
  94  * <p>
  95  * This class models a quantity or amount of time in terms of years, months and days.
  96  * See {@link Duration} for the time-based equivalent to this class.
  97  * <p>
  98  * Durations and periods differ in their treatment of daylight savings time
  99  * when added to {@link ZonedDateTime}. A {@code Duration} will add an exact
 100  * number of seconds, thus a duration of one day is always exactly 24 hours.
 101  * By contrast, a {@code Period} will add a conceptual day, trying to maintain
 102  * the local time.
 103  * <p>
 104  * For example, consider adding a period of one day and a duration of one day to
 105  * 18:00 on the evening before a daylight savings gap. The {@code Period} will add
 106  * the conceptual day and result in a {@code ZonedDateTime} at 18:00 the following day.
 107  * By contrast, the {@code Duration} will add exactly 24 hours, resulting in a
 108  * {@code ZonedDateTime} at 19:00 the following day (assuming a one hour DST gap).
 109  * <p>
 110  * The supported units of a period are {@link ChronoUnit#YEARS YEARS},
 111  * {@link ChronoUnit#MONTHS MONTHS} and {@link ChronoUnit#DAYS DAYS}.
 112  * All three fields are always present, but may be set to zero.
 113  * <p>
 114  * The ISO-8601 calendar system is the modern civil calendar system used today
 115  * in most of the world. It is equivalent to the proleptic Gregorian calendar
 116  * system, in which today's rules for leap years are applied for all time.
 117  * <p>
 118  * The period is modeled as a directed amount of time, meaning that individual parts of the
 119  * period may be negative.
 120  *
 121  * <p>
 122  * This is a <a href="{@docRoot}/java.base/java/lang/doc-files/ValueBased.html">value-based</a>
 123  * class; use of identity-sensitive operations (including reference equality
 124  * ({@code ==}), identity hash code, or synchronization) on instances of
 125  * {@code Period} may have unpredictable results and should be avoided.
 126  * The {@code equals} method should be used for comparisons.
 127  *
 128  * @implSpec
 129  * This class is immutable and thread-safe.
 130  *
 131  * @since 1.8
 132  */
 133 public final class Period
 134         implements ChronoPeriod, Serializable {
 135 
 136     /**
 137      * A constant for a period of zero.
 138      */
 139     public static final Period ZERO = new Period(0, 0, 0);
 140     /**
 141      * Serialization version.
 142      */
 143     @java.io.Serial
 144     private static final long serialVersionUID = -3587258372562876L;
 145     /**
 146      * The pattern for parsing.
 147      */
 148     private static final Pattern PATTERN =
 149             Pattern.compile("([-+]?)P(?:([-+]?[0-9]+)Y)?(?:([-+]?[0-9]+)M)?(?:([-+]?[0-9]+)W)?(?:([-+]?[0-9]+)D)?", Pattern.CASE_INSENSITIVE);
 150 
 151     /**
 152      * The set of supported units.
 153      */
 154     private static final List<TemporalUnit> SUPPORTED_UNITS = List.of(YEARS, MONTHS, DAYS);
 155 
 156     /**
 157      * The number of years.
 158      */
 159     private final int years;
 160     /**
 161      * The number of months.
 162      */
 163     private final int months;
 164     /**
 165      * The number of days.
 166      */
 167     private final int days;
 168 
 169     //-----------------------------------------------------------------------
 170     /**
 171      * Obtains a {@code Period} representing a number of years.
 172      * <p>
 173      * The resulting period will have the specified years.
 174      * The months and days units will be zero.
 175      *
 176      * @param years  the number of years, positive or negative
 177      * @return the period of years, not null
 178      */
 179     public static Period ofYears(int years) {
 180         return create(years, 0, 0);
 181     }
 182 
 183     /**
 184      * Obtains a {@code Period} representing a number of months.
 185      * <p>
 186      * The resulting period will have the specified months.
 187      * The years and days units will be zero.
 188      *
 189      * @param months  the number of months, positive or negative
 190      * @return the period of months, not null
 191      */
 192     public static Period ofMonths(int months) {
 193         return create(0, months, 0);
 194     }
 195 
 196     /**
 197      * Obtains a {@code Period} representing a number of weeks.
 198      * <p>
 199      * The resulting period will be day-based, with the amount of days
 200      * equal to the number of weeks multiplied by 7.
 201      * The years and months units will be zero.
 202      *
 203      * @param weeks  the number of weeks, positive or negative
 204      * @return the period, with the input weeks converted to days, not null
 205      */
 206     public static Period ofWeeks(int weeks) {
 207         return create(0, 0, Math.multiplyExact(weeks, 7));
 208     }
 209 
 210     /**
 211      * Obtains a {@code Period} representing a number of days.
 212      * <p>
 213      * The resulting period will have the specified days.
 214      * The years and months units will be zero.
 215      *
 216      * @param days  the number of days, positive or negative
 217      * @return the period of days, not null
 218      */
 219     public static Period ofDays(int days) {
 220         return create(0, 0, days);
 221     }
 222 
 223     //-----------------------------------------------------------------------
 224     /**
 225      * Obtains a {@code Period} representing a number of years, months and days.
 226      * <p>
 227      * This creates an instance based on years, months and days.
 228      *
 229      * @param years  the amount of years, may be negative
 230      * @param months  the amount of months, may be negative
 231      * @param days  the amount of days, may be negative
 232      * @return the period of years, months and days, not null
 233      */
 234     public static Period of(int years, int months, int days) {
 235         return create(years, months, days);
 236     }
 237 
 238     //-----------------------------------------------------------------------
 239     /**
 240      * Obtains an instance of {@code Period} from a temporal amount.
 241      * <p>
 242      * This obtains a period based on the specified amount.
 243      * A {@code TemporalAmount} represents an  amount of time, which may be
 244      * date-based or time-based, which this factory extracts to a {@code Period}.
 245      * <p>
 246      * The conversion loops around the set of units from the amount and uses
 247      * the {@link ChronoUnit#YEARS YEARS}, {@link ChronoUnit#MONTHS MONTHS}
 248      * and {@link ChronoUnit#DAYS DAYS} units to create a period.
 249      * If any other units are found then an exception is thrown.
 250      * <p>
 251      * If the amount is a {@code ChronoPeriod} then it must use the ISO chronology.
 252      *
 253      * @param amount  the temporal amount to convert, not null
 254      * @return the equivalent period, not null
 255      * @throws DateTimeException if unable to convert to a {@code Period}
 256      * @throws ArithmeticException if the amount of years, months or days exceeds an int
 257      */
 258     public static Period from(TemporalAmount amount) {
 259         if (amount instanceof Period) {
 260             return (Period) amount;
 261         }
 262         if (amount instanceof ChronoPeriod) {
 263             if (IsoChronology.INSTANCE.equals(((ChronoPeriod) amount).getChronology()) == false) {
 264                 throw new DateTimeException("Period requires ISO chronology: " + amount);
 265             }
 266         }
 267         Objects.requireNonNull(amount, "amount");
 268         int years = 0;
 269         int months = 0;
 270         int days = 0;
 271         for (TemporalUnit unit : amount.getUnits()) {
 272             long unitAmount = amount.get(unit);
 273             if (unit == ChronoUnit.YEARS) {
 274                 years = Math.toIntExact(unitAmount);
 275             } else if (unit == ChronoUnit.MONTHS) {
 276                 months = Math.toIntExact(unitAmount);
 277             } else if (unit == ChronoUnit.DAYS) {
 278                 days = Math.toIntExact(unitAmount);
 279             } else {
 280                 throw new DateTimeException("Unit must be Years, Months or Days, but was " + unit);
 281             }
 282         }
 283         return create(years, months, days);
 284     }
 285 
 286     //-----------------------------------------------------------------------
 287     /**
 288      * Obtains a {@code Period} from a text string such as {@code PnYnMnD}.
 289      * <p>
 290      * This will parse the string produced by {@code toString()} which is
 291      * based on the ISO-8601 period formats {@code PnYnMnD} and {@code PnW}.
 292      * <p>
 293      * The string starts with an optional sign, denoted by the ASCII negative
 294      * or positive symbol. If negative, the whole period is negated.
 295      * The ASCII letter "P" is next in upper or lower case.
 296      * There are then four sections, each consisting of a number and a suffix.
 297      * At least one of the four sections must be present.
 298      * The sections have suffixes in ASCII of "Y", "M", "W" and "D" for
 299      * years, months, weeks and days, accepted in upper or lower case.
 300      * The suffixes must occur in order.
 301      * The number part of each section must consist of ASCII digits.
 302      * The number may be prefixed by the ASCII negative or positive symbol.
 303      * The number must parse to an {@code int}.
 304      * <p>
 305      * The leading plus/minus sign, and negative values for other units are
 306      * not part of the ISO-8601 standard. In addition, ISO-8601 does not
 307      * permit mixing between the {@code PnYnMnD} and {@code PnW} formats.
 308      * Any week-based input is multiplied by 7 and treated as a number of days.
 309      * <p>
 310      * For example, the following are valid inputs:
 311      * <pre>
 312      *   "P2Y"             -- Period.ofYears(2)
 313      *   "P3M"             -- Period.ofMonths(3)
 314      *   "P4W"             -- Period.ofWeeks(4)
 315      *   "P5D"             -- Period.ofDays(5)
 316      *   "P1Y2M3D"         -- Period.of(1, 2, 3)
 317      *   "P1Y2M3W4D"       -- Period.of(1, 2, 25)
 318      *   "P-1Y2M"          -- Period.of(-1, 2, 0)
 319      *   "-P1Y2M"          -- Period.of(-1, -2, 0)
 320      * </pre>
 321      *
 322      * @param text  the text to parse, not null
 323      * @return the parsed period, not null
 324      * @throws DateTimeParseException if the text cannot be parsed to a period
 325      */
 326     public static Period parse(CharSequence text) {
 327         Objects.requireNonNull(text, "text");
 328         Matcher matcher = PATTERN.matcher(text);
 329         if (matcher.matches()) {
 330             int negate = (charMatch(text, matcher.start(1), matcher.end(1), '-') ? -1 : 1);
 331             int yearStart = matcher.start(2), yearEnd = matcher.end(2);
 332             int monthStart = matcher.start(3), monthEnd = matcher.end(3);
 333             int weekStart = matcher.start(4), weekEnd = matcher.end(4);
 334             int dayStart = matcher.start(5), dayEnd = matcher.end(5);
 335             if (yearStart >= 0 || monthStart >= 0 || weekStart >= 0 || dayStart >= 0) {
 336                 try {
 337                     int years = parseNumber(text, yearStart, yearEnd, negate);
 338                     int months = parseNumber(text, monthStart, monthEnd, negate);
 339                     int weeks = parseNumber(text, weekStart, weekEnd, negate);
 340                     int days = parseNumber(text, dayStart, dayEnd, negate);
 341                     days = Math.addExact(days, Math.multiplyExact(weeks, 7));
 342                     return create(years, months, days);
 343                 } catch (NumberFormatException ex) {
 344                     throw new DateTimeParseException("Text cannot be parsed to a Period", text, 0, ex);
 345                 }
 346             }
 347         }
 348         throw new DateTimeParseException("Text cannot be parsed to a Period", text, 0);
 349     }
 350 
 351     private static boolean charMatch(CharSequence text, int start, int end, char c) {
 352         return (start >= 0 && end == start + 1 && text.charAt(start) == c);
 353     }
 354 
 355     private static int parseNumber(CharSequence text, int start, int end, int negate) {
 356         if (start < 0 || end < 0) {
 357             return 0;
 358         }
 359         int val = Integer.parseInt(text, start, end, 10);
 360         try {
 361             return Math.multiplyExact(val, negate);
 362         } catch (ArithmeticException ex) {
 363             throw new DateTimeParseException("Text cannot be parsed to a Period", text, 0, ex);
 364         }
 365     }
 366 
 367     //-----------------------------------------------------------------------
 368     /**
 369      * Obtains a {@code Period} consisting of the number of years, months,
 370      * and days between two dates.
 371      * <p>
 372      * The start date is included, but the end date is not.
 373      * The period is calculated by removing complete months, then calculating
 374      * the remaining number of days, adjusting to ensure that both have the same sign.
 375      * The number of months is then split into years and months based on a 12 month year.
 376      * A month is considered if the end day-of-month is greater than or equal to the start day-of-month.
 377      * For example, from {@code 2010-01-15} to {@code 2011-03-18} is one year, two months and three days.
 378      * <p>
 379      * The result of this method can be a negative period if the end is before the start.
 380      * The negative sign will be the same in each of year, month and day.
 381      *
 382      * @param startDateInclusive  the start date, inclusive, not null
 383      * @param endDateExclusive  the end date, exclusive, not null
 384      * @return the period between this date and the end date, not null
 385      * @see ChronoLocalDate#until(ChronoLocalDate)
 386      */
 387     public static Period between(LocalDate startDateInclusive, LocalDate endDateExclusive) {
 388         return startDateInclusive.until(endDateExclusive);
 389     }
 390 
 391     //-----------------------------------------------------------------------
 392     /**
 393      * Creates an instance.
 394      *
 395      * @param years  the amount
 396      * @param months  the amount
 397      * @param days  the amount
 398      */
 399     private static Period create(int years, int months, int days) {
 400         if ((years | months | days) == 0) {
 401             return ZERO;
 402         }
 403         return new Period(years, months, days);
 404     }
 405 
 406     /**
 407      * Constructor.
 408      *
 409      * @param years  the amount
 410      * @param months  the amount
 411      * @param days  the amount
 412      */
 413     private Period(int years, int months, int days) {
 414         this.years = years;
 415         this.months = months;
 416         this.days = days;
 417     }
 418 
 419     //-----------------------------------------------------------------------
 420     /**
 421      * Gets the value of the requested unit.
 422      * <p>
 423      * This returns a value for each of the three supported units,
 424      * {@link ChronoUnit#YEARS YEARS}, {@link ChronoUnit#MONTHS MONTHS} and
 425      * {@link ChronoUnit#DAYS DAYS}.
 426      * All other units throw an exception.
 427      *
 428      * @param unit the {@code TemporalUnit} for which to return the value
 429      * @return the long value of the unit
 430      * @throws DateTimeException if the unit is not supported
 431      * @throws UnsupportedTemporalTypeException if the unit is not supported
 432      */
 433     @Override
 434     public long get(TemporalUnit unit) {
 435         if (unit == ChronoUnit.YEARS) {
 436             return getYears();
 437         } else if (unit == ChronoUnit.MONTHS) {
 438             return getMonths();
 439         } else if (unit == ChronoUnit.DAYS) {
 440             return getDays();
 441         } else {
 442             throw new UnsupportedTemporalTypeException("Unsupported unit: " + unit);
 443         }
 444     }
 445 
 446     /**
 447      * Gets the set of units supported by this period.
 448      * <p>
 449      * The supported units are {@link ChronoUnit#YEARS YEARS},
 450      * {@link ChronoUnit#MONTHS MONTHS} and {@link ChronoUnit#DAYS DAYS}.
 451      * They are returned in the order years, months, days.
 452      * <p>
 453      * This set can be used in conjunction with {@link #get(TemporalUnit)}
 454      * to access the entire state of the period.
 455      *
 456      * @return a list containing the years, months and days units, not null
 457      */
 458     @Override
 459     public List<TemporalUnit> getUnits() {
 460         return SUPPORTED_UNITS;
 461     }
 462 
 463     /**
 464      * Gets the chronology of this period, which is the ISO calendar system.
 465      * <p>
 466      * The {@code Chronology} represents the calendar system in use.
 467      * The ISO-8601 calendar system is the modern civil calendar system used today
 468      * in most of the world. It is equivalent to the proleptic Gregorian calendar
 469      * system, in which today's rules for leap years are applied for all time.
 470      *
 471      * @return the ISO chronology, not null
 472      */
 473     @Override
 474     public IsoChronology getChronology() {
 475         return IsoChronology.INSTANCE;
 476     }
 477 
 478     //-----------------------------------------------------------------------
 479     /**
 480      * Checks if all three units of this period are zero.
 481      * <p>
 482      * A zero period has the value zero for the years, months and days units.
 483      *
 484      * @return true if this period is zero-length
 485      */
 486     public boolean isZero() {
 487         return (this == ZERO);
 488     }
 489 
 490     /**
 491      * Checks if any of the three units of this period are negative.
 492      * <p>
 493      * This checks whether the years, months or days units are less than zero.
 494      *
 495      * @return true if any unit of this period is negative
 496      */
 497     public boolean isNegative() {
 498         return years < 0 || months < 0 || days < 0;
 499     }
 500 
 501     //-----------------------------------------------------------------------
 502     /**
 503      * Gets the amount of years of this period.
 504      * <p>
 505      * This returns the years unit.
 506      * <p>
 507      * The months unit is not automatically normalized with the years unit.
 508      * This means that a period of "15 months" is different to a period
 509      * of "1 year and 3 months".
 510      *
 511      * @return the amount of years of this period, may be negative
 512      */
 513     public int getYears() {
 514         return years;
 515     }
 516 
 517     /**
 518      * Gets the amount of months of this period.
 519      * <p>
 520      * This returns the months unit.
 521      * <p>
 522      * The months unit is not automatically normalized with the years unit.
 523      * This means that a period of "15 months" is different to a period
 524      * of "1 year and 3 months".
 525      *
 526      * @return the amount of months of this period, may be negative
 527      */
 528     public int getMonths() {
 529         return months;
 530     }
 531 
 532     /**
 533      * Gets the amount of days of this period.
 534      * <p>
 535      * This returns the days unit.
 536      *
 537      * @return the amount of days of this period, may be negative
 538      */
 539     public int getDays() {
 540         return days;
 541     }
 542 
 543     //-----------------------------------------------------------------------
 544     /**
 545      * Returns a copy of this period with the specified amount of years.
 546      * <p>
 547      * This sets the amount of the years unit in a copy of this period.
 548      * The months and days units are unaffected.
 549      * <p>
 550      * The months unit is not automatically normalized with the years unit.
 551      * This means that a period of "15 months" is different to a period
 552      * of "1 year and 3 months".
 553      * <p>
 554      * This instance is immutable and unaffected by this method call.
 555      *
 556      * @param years  the years to represent, may be negative
 557      * @return a {@code Period} based on this period with the requested years, not null
 558      */
 559     public Period withYears(int years) {
 560         if (years == this.years) {
 561             return this;
 562         }
 563         return create(years, months, days);
 564     }
 565 
 566     /**
 567      * Returns a copy of this period with the specified amount of months.
 568      * <p>
 569      * This sets the amount of the months unit in a copy of this period.
 570      * The years and days units are unaffected.
 571      * <p>
 572      * The months unit is not automatically normalized with the years unit.
 573      * This means that a period of "15 months" is different to a period
 574      * of "1 year and 3 months".
 575      * <p>
 576      * This instance is immutable and unaffected by this method call.
 577      *
 578      * @param months  the months to represent, may be negative
 579      * @return a {@code Period} based on this period with the requested months, not null
 580      */
 581     public Period withMonths(int months) {
 582         if (months == this.months) {
 583             return this;
 584         }
 585         return create(years, months, days);
 586     }
 587 
 588     /**
 589      * Returns a copy of this period with the specified amount of days.
 590      * <p>
 591      * This sets the amount of the days unit in a copy of this period.
 592      * The years and months units are unaffected.
 593      * <p>
 594      * This instance is immutable and unaffected by this method call.
 595      *
 596      * @param days  the days to represent, may be negative
 597      * @return a {@code Period} based on this period with the requested days, not null
 598      */
 599     public Period withDays(int days) {
 600         if (days == this.days) {
 601             return this;
 602         }
 603         return create(years, months, days);
 604     }
 605 
 606     //-----------------------------------------------------------------------
 607     /**
 608      * Returns a copy of this period with the specified period added.
 609      * <p>
 610      * This operates separately on the years, months and days.
 611      * No normalization is performed.
 612      * <p>
 613      * For example, "1 year, 6 months and 3 days" plus "2 years, 2 months and 2 days"
 614      * returns "3 years, 8 months and 5 days".
 615      * <p>
 616      * The specified amount is typically an instance of {@code Period}.
 617      * Other types are interpreted using {@link Period#from(TemporalAmount)}.
 618      * <p>
 619      * This instance is immutable and unaffected by this method call.
 620      *
 621      * @param amountToAdd  the amount to add, not null
 622      * @return a {@code Period} based on this period with the requested period added, not null
 623      * @throws DateTimeException if the specified amount has a non-ISO chronology or
 624      *  contains an invalid unit
 625      * @throws ArithmeticException if numeric overflow occurs
 626      */
 627     public Period plus(TemporalAmount amountToAdd) {
 628         Period isoAmount = Period.from(amountToAdd);
 629         return create(
 630                 Math.addExact(years, isoAmount.years),
 631                 Math.addExact(months, isoAmount.months),
 632                 Math.addExact(days, isoAmount.days));
 633     }
 634 
 635     /**
 636      * Returns a copy of this period with the specified years added.
 637      * <p>
 638      * This adds the amount to the years unit in a copy of this period.
 639      * The months and days units are unaffected.
 640      * For example, "1 year, 6 months and 3 days" plus 2 years returns "3 years, 6 months and 3 days".
 641      * <p>
 642      * This instance is immutable and unaffected by this method call.
 643      *
 644      * @param yearsToAdd  the years to add, positive or negative
 645      * @return a {@code Period} based on this period with the specified years added, not null
 646      * @throws ArithmeticException if numeric overflow occurs
 647      */
 648     public Period plusYears(long yearsToAdd) {
 649         if (yearsToAdd == 0) {
 650             return this;
 651         }
 652         return create(Math.toIntExact(Math.addExact(years, yearsToAdd)), months, days);
 653     }
 654 
 655     /**
 656      * Returns a copy of this period with the specified months added.
 657      * <p>
 658      * This adds the amount to the months unit in a copy of this period.
 659      * The years and days units are unaffected.
 660      * For example, "1 year, 6 months and 3 days" plus 2 months returns "1 year, 8 months and 3 days".
 661      * <p>
 662      * This instance is immutable and unaffected by this method call.
 663      *
 664      * @param monthsToAdd  the months to add, positive or negative
 665      * @return a {@code Period} based on this period with the specified months added, not null
 666      * @throws ArithmeticException if numeric overflow occurs
 667      */
 668     public Period plusMonths(long monthsToAdd) {
 669         if (monthsToAdd == 0) {
 670             return this;
 671         }
 672         return create(years, Math.toIntExact(Math.addExact(months, monthsToAdd)), days);
 673     }
 674 
 675     /**
 676      * Returns a copy of this period with the specified days added.
 677      * <p>
 678      * This adds the amount to the days unit in a copy of this period.
 679      * The years and months units are unaffected.
 680      * For example, "1 year, 6 months and 3 days" plus 2 days returns "1 year, 6 months and 5 days".
 681      * <p>
 682      * This instance is immutable and unaffected by this method call.
 683      *
 684      * @param daysToAdd  the days to add, positive or negative
 685      * @return a {@code Period} based on this period with the specified days added, not null
 686      * @throws ArithmeticException if numeric overflow occurs
 687      */
 688     public Period plusDays(long daysToAdd) {
 689         if (daysToAdd == 0) {
 690             return this;
 691         }
 692         return create(years, months, Math.toIntExact(Math.addExact(days, daysToAdd)));
 693     }
 694 
 695     //-----------------------------------------------------------------------
 696     /**
 697      * Returns a copy of this period with the specified period subtracted.
 698      * <p>
 699      * This operates separately on the years, months and days.
 700      * No normalization is performed.
 701      * <p>
 702      * For example, "1 year, 6 months and 3 days" minus "2 years, 2 months and 2 days"
 703      * returns "-1 years, 4 months and 1 day".
 704      * <p>
 705      * The specified amount is typically an instance of {@code Period}.
 706      * Other types are interpreted using {@link Period#from(TemporalAmount)}.
 707      * <p>
 708      * This instance is immutable and unaffected by this method call.
 709      *
 710      * @param amountToSubtract  the amount to subtract, not null
 711      * @return a {@code Period} based on this period with the requested period subtracted, not null
 712      * @throws DateTimeException if the specified amount has a non-ISO chronology or
 713      *  contains an invalid unit
 714      * @throws ArithmeticException if numeric overflow occurs
 715      */
 716     public Period minus(TemporalAmount amountToSubtract) {
 717         Period isoAmount = Period.from(amountToSubtract);
 718         return create(
 719                 Math.subtractExact(years, isoAmount.years),
 720                 Math.subtractExact(months, isoAmount.months),
 721                 Math.subtractExact(days, isoAmount.days));
 722     }
 723 
 724     /**
 725      * Returns a copy of this period with the specified years subtracted.
 726      * <p>
 727      * This subtracts the amount from the years unit in a copy of this period.
 728      * The months and days units are unaffected.
 729      * For example, "1 year, 6 months and 3 days" minus 2 years returns "-1 years, 6 months and 3 days".
 730      * <p>
 731      * This instance is immutable and unaffected by this method call.
 732      *
 733      * @param yearsToSubtract  the years to subtract, positive or negative
 734      * @return a {@code Period} based on this period with the specified years subtracted, not null
 735      * @throws ArithmeticException if numeric overflow occurs
 736      */
 737     public Period minusYears(long yearsToSubtract) {
 738         return (yearsToSubtract == Long.MIN_VALUE ? plusYears(Long.MAX_VALUE).plusYears(1) : plusYears(-yearsToSubtract));
 739     }
 740 
 741     /**
 742      * Returns a copy of this period with the specified months subtracted.
 743      * <p>
 744      * This subtracts the amount from the months unit in a copy of this period.
 745      * The years and days units are unaffected.
 746      * For example, "1 year, 6 months and 3 days" minus 2 months returns "1 year, 4 months and 3 days".
 747      * <p>
 748      * This instance is immutable and unaffected by this method call.
 749      *
 750      * @param monthsToSubtract  the years to subtract, positive or negative
 751      * @return a {@code Period} based on this period with the specified months subtracted, not null
 752      * @throws ArithmeticException if numeric overflow occurs
 753      */
 754     public Period minusMonths(long monthsToSubtract) {
 755         return (monthsToSubtract == Long.MIN_VALUE ? plusMonths(Long.MAX_VALUE).plusMonths(1) : plusMonths(-monthsToSubtract));
 756     }
 757 
 758     /**
 759      * Returns a copy of this period with the specified days subtracted.
 760      * <p>
 761      * This subtracts the amount from the days unit in a copy of this period.
 762      * The years and months units are unaffected.
 763      * For example, "1 year, 6 months and 3 days" minus 2 days returns "1 year, 6 months and 1 day".
 764      * <p>
 765      * This instance is immutable and unaffected by this method call.
 766      *
 767      * @param daysToSubtract  the months to subtract, positive or negative
 768      * @return a {@code Period} based on this period with the specified days subtracted, not null
 769      * @throws ArithmeticException if numeric overflow occurs
 770      */
 771     public Period minusDays(long daysToSubtract) {
 772         return (daysToSubtract == Long.MIN_VALUE ? plusDays(Long.MAX_VALUE).plusDays(1) : plusDays(-daysToSubtract));
 773     }
 774 
 775     //-----------------------------------------------------------------------
 776     /**
 777      * Returns a new instance with each element in this period multiplied
 778      * by the specified scalar.
 779      * <p>
 780      * This returns a period with each of the years, months and days units
 781      * individually multiplied.
 782      * For example, a period of "2 years, -3 months and 4 days" multiplied by
 783      * 3 will return "6 years, -9 months and 12 days".
 784      * No normalization is performed.
 785      *
 786      * @param scalar  the scalar to multiply by, not null
 787      * @return a {@code Period} based on this period with the amounts multiplied by the scalar, not null
 788      * @throws ArithmeticException if numeric overflow occurs
 789      */
 790     public Period multipliedBy(int scalar) {
 791         if (this == ZERO || scalar == 1) {
 792             return this;
 793         }
 794         return create(
 795                 Math.multiplyExact(years, scalar),
 796                 Math.multiplyExact(months, scalar),
 797                 Math.multiplyExact(days, scalar));
 798     }
 799 
 800     /**
 801      * Returns a new instance with each amount in this period negated.
 802      * <p>
 803      * This returns a period with each of the years, months and days units
 804      * individually negated.
 805      * For example, a period of "2 years, -3 months and 4 days" will be
 806      * negated to "-2 years, 3 months and -4 days".
 807      * No normalization is performed.
 808      *
 809      * @return a {@code Period} based on this period with the amounts negated, not null
 810      * @throws ArithmeticException if numeric overflow occurs, which only happens if
 811      *  one of the units has the value {@code Long.MIN_VALUE}
 812      */
 813     public Period negated() {
 814         return multipliedBy(-1);
 815     }
 816 
 817     //-----------------------------------------------------------------------
 818     /**
 819      * Returns a copy of this period with the years and months normalized.
 820      * <p>
 821      * This normalizes the years and months units, leaving the days unit unchanged.
 822      * The months unit is adjusted to have an absolute value less than 12,
 823      * with the years unit being adjusted to compensate. For example, a period of
 824      * "1 Year and 15 months" will be normalized to "2 years and 3 months".
 825      * <p>
 826      * The sign of the years and months units will be the same after normalization.
 827      * For example, a period of "1 year and -25 months" will be normalized to
 828      * "-1 year and -1 month".
 829      * <p>
 830      * This instance is immutable and unaffected by this method call.
 831      *
 832      * @return a {@code Period} based on this period with excess months normalized to years, not null
 833      * @throws ArithmeticException if numeric overflow occurs
 834      */
 835     public Period normalized() {
 836         long totalMonths = toTotalMonths();
 837         long splitYears = totalMonths / 12;
 838         int splitMonths = (int) (totalMonths % 12);  // no overflow
 839         if (splitYears == years && splitMonths == months) {
 840             return this;
 841         }
 842         return create(Math.toIntExact(splitYears), splitMonths, days);
 843     }
 844 
 845     /**
 846      * Gets the total number of months in this period.
 847      * <p>
 848      * This returns the total number of months in the period by multiplying the
 849      * number of years by 12 and adding the number of months.
 850      * <p>
 851      * This instance is immutable and unaffected by this method call.
 852      *
 853      * @return the total number of months in the period, may be negative
 854      */
 855     public long toTotalMonths() {
 856         return years * 12L + months;  // no overflow
 857     }
 858 
 859     //-------------------------------------------------------------------------
 860     /**
 861      * Adds this period to the specified temporal object.
 862      * <p>
 863      * This returns a temporal object of the same observable type as the input
 864      * with this period added.
 865      * If the temporal has a chronology, it must be the ISO chronology.
 866      * <p>
 867      * In most cases, it is clearer to reverse the calling pattern by using
 868      * {@link Temporal#plus(TemporalAmount)}.
 869      * <pre>
 870      *   // these two lines are equivalent, but the second approach is recommended
 871      *   dateTime = thisPeriod.addTo(dateTime);
 872      *   dateTime = dateTime.plus(thisPeriod);
 873      * </pre>
 874      * <p>
 875      * The calculation operates as follows.
 876      * First, the chronology of the temporal is checked to ensure it is ISO chronology or null.
 877      * Second, if the months are zero, the years are added if non-zero, otherwise
 878      * the combination of years and months is added if non-zero.
 879      * Finally, any days are added.
 880      * <p>
 881      * This approach ensures that a partial period can be added to a partial date.
 882      * For example, a period of years and/or months can be added to a {@code YearMonth},
 883      * but a period including days cannot.
 884      * The approach also adds years and months together when necessary, which ensures
 885      * correct behaviour at the end of the month.
 886      * <p>
 887      * This instance is immutable and unaffected by this method call.
 888      *
 889      * @param temporal  the temporal object to adjust, not null
 890      * @return an object of the same type with the adjustment made, not null
 891      * @throws DateTimeException if unable to add
 892      * @throws ArithmeticException if numeric overflow occurs
 893      */
 894     @Override
 895     public Temporal addTo(Temporal temporal) {
 896         validateChrono(temporal);
 897         if (months == 0) {
 898             if (years != 0) {
 899                 temporal = temporal.plus(years, YEARS);
 900             }
 901         } else {
 902             long totalMonths = toTotalMonths();
 903             if (totalMonths != 0) {
 904                 temporal = temporal.plus(totalMonths, MONTHS);
 905             }
 906         }
 907         if (days != 0) {
 908             temporal = temporal.plus(days, DAYS);
 909         }
 910         return temporal;
 911     }
 912 
 913     /**
 914      * Subtracts this period from the specified temporal object.
 915      * <p>
 916      * This returns a temporal object of the same observable type as the input
 917      * with this period subtracted.
 918      * If the temporal has a chronology, it must be the ISO chronology.
 919      * <p>
 920      * In most cases, it is clearer to reverse the calling pattern by using
 921      * {@link Temporal#minus(TemporalAmount)}.
 922      * <pre>
 923      *   // these two lines are equivalent, but the second approach is recommended
 924      *   dateTime = thisPeriod.subtractFrom(dateTime);
 925      *   dateTime = dateTime.minus(thisPeriod);
 926      * </pre>
 927      * <p>
 928      * The calculation operates as follows.
 929      * First, the chronology of the temporal is checked to ensure it is ISO chronology or null.
 930      * Second, if the months are zero, the years are subtracted if non-zero, otherwise
 931      * the combination of years and months is subtracted if non-zero.
 932      * Finally, any days are subtracted.
 933      * <p>
 934      * This approach ensures that a partial period can be subtracted from a partial date.
 935      * For example, a period of years and/or months can be subtracted from a {@code YearMonth},
 936      * but a period including days cannot.
 937      * The approach also subtracts years and months together when necessary, which ensures
 938      * correct behaviour at the end of the month.
 939      * <p>
 940      * This instance is immutable and unaffected by this method call.
 941      *
 942      * @param temporal  the temporal object to adjust, not null
 943      * @return an object of the same type with the adjustment made, not null
 944      * @throws DateTimeException if unable to subtract
 945      * @throws ArithmeticException if numeric overflow occurs
 946      */
 947     @Override
 948     public Temporal subtractFrom(Temporal temporal) {
 949         validateChrono(temporal);
 950         if (months == 0) {
 951             if (years != 0) {
 952                 temporal = temporal.minus(years, YEARS);
 953             }
 954         } else {
 955             long totalMonths = toTotalMonths();
 956             if (totalMonths != 0) {
 957                 temporal = temporal.minus(totalMonths, MONTHS);
 958             }
 959         }
 960         if (days != 0) {
 961             temporal = temporal.minus(days, DAYS);
 962         }
 963         return temporal;
 964     }
 965 
 966     /**
 967      * Validates that the temporal has the correct chronology.
 968      */
 969     private void validateChrono(TemporalAccessor temporal) {
 970         Objects.requireNonNull(temporal, "temporal");
 971         Chronology temporalChrono = temporal.query(TemporalQueries.chronology());
 972         if (temporalChrono != null && IsoChronology.INSTANCE.equals(temporalChrono) == false) {
 973             throw new DateTimeException("Chronology mismatch, expected: ISO, actual: " + temporalChrono.getId());
 974         }
 975     }
 976 
 977     //-----------------------------------------------------------------------
 978     /**
 979      * Checks if this period is equal to another period.
 980      * <p>
 981      * The comparison is based on the type {@code Period} and each of the three amounts.
 982      * To be equal, the years, months and days units must be individually equal.
 983      * Note that this means that a period of "15 Months" is not equal to a period
 984      * of "1 Year and 3 Months".
 985      *
 986      * @param obj  the object to check, null returns false
 987      * @return true if this is equal to the other period
 988      */
 989     @Override
 990     public boolean equals(Object obj) {
 991         if (this == obj) {
 992             return true;
 993         }
 994         if (obj instanceof Period) {
 995             Period other = (Period) obj;
 996             return years == other.years &&
 997                     months == other.months &&
 998                     days == other.days;
 999         }
1000         return false;
1001     }
1002 
1003     /**
1004      * A hash code for this period.
1005      *
1006      * @return a suitable hash code
1007      */
1008     @Override
1009     public int hashCode() {
1010         return years + Integer.rotateLeft(months, 8) + Integer.rotateLeft(days, 16);
1011     }
1012 
1013     //-----------------------------------------------------------------------
1014     /**
1015      * Outputs this period as a {@code String}, such as {@code P6Y3M1D}.
1016      * <p>
1017      * The output will be in the ISO-8601 period format.
1018      * A zero period will be represented as zero days, 'P0D'.
1019      *
1020      * @return a string representation of this period, not null
1021      */
1022     @Override
1023     public String toString() {
1024         if (this == ZERO) {
1025             return "P0D";
1026         } else {
1027             StringBuilder buf = new StringBuilder();
1028             buf.append('P');
1029             if (years != 0) {
1030                 buf.append(years).append('Y');
1031             }
1032             if (months != 0) {
1033                 buf.append(months).append('M');
1034             }
1035             if (days != 0) {
1036                 buf.append(days).append('D');
1037             }
1038             return buf.toString();
1039         }
1040     }
1041 
1042     //-----------------------------------------------------------------------
1043     /**
1044      * Writes the object using a
1045      * <a href="{@docRoot}/serialized-form.html#java.time.Ser">dedicated serialized form</a>.
1046      * @serialData
1047      * <pre>
1048      *  out.writeByte(14);  // identifies a Period
1049      *  out.writeInt(years);
1050      *  out.writeInt(months);
1051      *  out.writeInt(days);
1052      * </pre>
1053      *
1054      * @return the instance of {@code Ser}, not null
1055      */
1056     @java.io.Serial
1057     private Object writeReplace() {
1058         return new Ser(Ser.PERIOD_TYPE, this);
1059     }
1060 
1061     /**
1062      * Defend against malicious streams.
1063      *
1064      * @param s the stream to read
1065      * @throws java.io.InvalidObjectException always
1066      */
1067     @java.io.Serial
1068     private void readObject(ObjectInputStream s) throws InvalidObjectException {
1069         throw new InvalidObjectException("Deserialization via serialization delegate");
1070     }
1071 
1072     void writeExternal(DataOutput out) throws IOException {
1073         out.writeInt(years);
1074         out.writeInt(months);
1075         out.writeInt(days);
1076     }
1077 
1078     static Period readExternal(DataInput in) throws IOException {
1079         int years = in.readInt();
1080         int months = in.readInt();
1081         int days = in.readInt();
1082         return Period.of(years, months, days);
1083     }
1084 
1085 }