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   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.
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  22  * or visit www.oracle.com if you need additional information or have any
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  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.OFFSET_SECONDS;
  65 
  66 import java.io.DataInput;
  67 import java.io.DataOutput;
  68 import java.io.IOException;
  69 import java.io.InvalidObjectException;
  70 import java.io.ObjectStreamException;
  71 import java.io.Serializable;
  72 import java.time.temporal.ChronoField;
  73 import java.time.temporal.Queries;
  74 import java.time.temporal.Temporal;
  75 import java.time.temporal.TemporalAccessor;
  76 import java.time.temporal.TemporalAdjuster;
  77 import java.time.temporal.TemporalField;
  78 import java.time.temporal.TemporalQuery;
  79 import java.time.temporal.ValueRange;
  80 import java.time.zone.ZoneRules;
  81 import java.util.Objects;
  82 import java.util.concurrent.ConcurrentHashMap;
  83 import java.util.concurrent.ConcurrentMap;
  84 
  85 /**
  86  * A time-zone offset from Greenwich/UTC, such as {@code +02:00}.
  87  * <p>
  88  * A time-zone offset is the period of time that a time-zone differs from Greenwich/UTC.
  89  * This is usually a fixed number of hours and minutes.
  90  * <p>
  91  * Different parts of the world have different time-zone offsets.
  92  * The rules for how offsets vary by place and time of year are captured in the
  93  * {@link ZoneId} class.
  94  * <p>
  95  * For example, Paris is one hour ahead of Greenwich/UTC in winter and two hours
  96  * ahead in summer. The {@code ZoneId} instance for Paris will reference two
  97  * {@code ZoneOffset} instances - a {@code +01:00} instance for winter,
  98  * and a {@code +02:00} instance for summer.
  99  * <p>
 100  * In 2008, time-zone offsets around the world extended from -12:00 to +14:00.
 101  * To prevent any problems with that range being extended, yet still provide
 102  * validation, the range of offsets is restricted to -18:00 to 18:00 inclusive.
 103  * <p>
 104  * This class is designed for use with the ISO calendar system.
 105  * The fields of hours, minutes and seconds make assumptions that are valid for the
 106  * standard ISO definitions of those fields. This class may be used with other
 107  * calendar systems providing the definition of the time fields matches those
 108  * of the ISO calendar system.
 109  * <p>
 110  * Instances of {@code ZoneOffset} must be compared using {@link #equals}.
 111  * Implementations may choose to cache certain common offsets, however
 112  * applications must not rely on such caching.
 113  *
 114  * <h3>Specification for implementors</h3>
 115  * This class is immutable and thread-safe.
 116  *
 117  * @since 1.8
 118  */
 119 public final class ZoneOffset
 120         extends ZoneId
 121         implements TemporalAccessor, TemporalAdjuster, Comparable<ZoneOffset>, Serializable {
 122 
 123     /** Cache of time-zone offset by offset in seconds. */
 124     private static final ConcurrentMap<Integer, ZoneOffset> SECONDS_CACHE = new ConcurrentHashMap<>(16, 0.75f, 4);
 125     /** Cache of time-zone offset by ID. */
 126     private static final ConcurrentMap<String, ZoneOffset> ID_CACHE = new ConcurrentHashMap<>(16, 0.75f, 4);
 127 
 128     /**
 129      * The number of seconds per hour.
 130      */
 131     private static final int SECONDS_PER_HOUR = 60 * 60;
 132     /**
 133      * The number of seconds per minute.
 134      */
 135     private static final int SECONDS_PER_MINUTE = 60;
 136     /**
 137      * The number of minutes per hour.
 138      */
 139     private static final int MINUTES_PER_HOUR = 60;
 140     /**
 141      * The abs maximum seconds.
 142      */
 143     private static final int MAX_SECONDS = 18 * SECONDS_PER_HOUR;
 144     /**
 145      * Serialization version.
 146      */
 147     private static final long serialVersionUID = 2357656521762053153L;
 148 
 149     /**
 150      * The time-zone offset for UTC, with an ID of 'Z'.
 151      */
 152     public static final ZoneOffset UTC = ZoneOffset.ofTotalSeconds(0);
 153     /**
 154      * Constant for the maximum supported offset.
 155      */
 156     public static final ZoneOffset MIN = ZoneOffset.ofTotalSeconds(-MAX_SECONDS);
 157     /**
 158      * Constant for the maximum supported offset.
 159      */
 160     public static final ZoneOffset MAX = ZoneOffset.ofTotalSeconds(MAX_SECONDS);
 161 
 162     /**
 163      * The total offset in seconds.
 164      */
 165     private final int totalSeconds;
 166     /**
 167      * The string form of the time-zone offset.
 168      */
 169     private final transient String id;
 170 
 171     //-----------------------------------------------------------------------
 172     /**
 173      * Obtains an instance of {@code ZoneOffset} using the ID.
 174      * <p>
 175      * This method parses the string ID of a {@code ZoneOffset} to
 176      * return an instance. The parsing accepts all the formats generated by
 177      * {@link #getId()}, plus some additional formats:
 178      * <p><ul>
 179      * <li>{@code Z} - for UTC
 180      * <li>{@code +h}
 181      * <li>{@code +hh}
 182      * <li>{@code +hh:mm}
 183      * <li>{@code -hh:mm}
 184      * <li>{@code +hhmm}
 185      * <li>{@code -hhmm}
 186      * <li>{@code +hh:mm:ss}
 187      * <li>{@code -hh:mm:ss}
 188      * <li>{@code +hhmmss}
 189      * <li>{@code -hhmmss}
 190      * </ul><p>
 191      * Note that &plusmn; means either the plus or minus symbol.
 192      * <p>
 193      * The ID of the returned offset will be normalized to one of the formats
 194      * described by {@link #getId()}.
 195      * <p>
 196      * The maximum supported range is from +18:00 to -18:00 inclusive.
 197      *
 198      * @param offsetId  the offset ID, not null
 199      * @return the zone-offset, not null
 200      * @throws DateTimeException if the offset ID is invalid
 201      */
 202     @SuppressWarnings("fallthrough")
 203     public static ZoneOffset of(String offsetId) {
 204         Objects.requireNonNull(offsetId, "offsetId");
 205         // "Z" is always in the cache
 206         ZoneOffset offset = ID_CACHE.get(offsetId);
 207         if (offset != null) {
 208             return offset;
 209         }
 210 
 211         // parse - +h, +hh, +hhmm, +hh:mm, +hhmmss, +hh:mm:ss
 212         final int hours, minutes, seconds;
 213         switch (offsetId.length()) {
 214             case 2:
 215                 offsetId = offsetId.charAt(0) + "0" + offsetId.charAt(1);  // fallthru
 216             case 3:
 217                 hours = parseNumber(offsetId, 1, false);
 218                 minutes = 0;
 219                 seconds = 0;
 220                 break;
 221             case 5:
 222                 hours = parseNumber(offsetId, 1, false);
 223                 minutes = parseNumber(offsetId, 3, false);
 224                 seconds = 0;
 225                 break;
 226             case 6:
 227                 hours = parseNumber(offsetId, 1, false);
 228                 minutes = parseNumber(offsetId, 4, true);
 229                 seconds = 0;
 230                 break;
 231             case 7:
 232                 hours = parseNumber(offsetId, 1, false);
 233                 minutes = parseNumber(offsetId, 3, false);
 234                 seconds = parseNumber(offsetId, 5, false);
 235                 break;
 236             case 9:
 237                 hours = parseNumber(offsetId, 1, false);
 238                 minutes = parseNumber(offsetId, 4, true);
 239                 seconds = parseNumber(offsetId, 7, true);
 240                 break;
 241             default:
 242                 throw new DateTimeException("Zone offset ID '" + offsetId + "' is invalid");
 243         }
 244         char first = offsetId.charAt(0);
 245         if (first != '+' && first != '-') {
 246             throw new DateTimeException("Zone offset ID '" + offsetId + "' is invalid: Plus/minus not found when expected");
 247         }
 248         if (first == '-') {
 249             return ofHoursMinutesSeconds(-hours, -minutes, -seconds);
 250         } else {
 251             return ofHoursMinutesSeconds(hours, minutes, seconds);
 252         }
 253     }
 254 
 255     /**
 256      * Parse a two digit zero-prefixed number.
 257      *
 258      * @param offsetId  the offset ID, not null
 259      * @param pos  the position to parse, valid
 260      * @param precededByColon  should this number be prefixed by a precededByColon
 261      * @return the parsed number, from 0 to 99
 262      */
 263     private static int parseNumber(CharSequence offsetId, int pos, boolean precededByColon) {
 264         if (precededByColon && offsetId.charAt(pos - 1) != ':') {
 265             throw new DateTimeException("Zone offset ID '" + offsetId + "' is invalid: Colon not found when expected");
 266         }
 267         char ch1 = offsetId.charAt(pos);
 268         char ch2 = offsetId.charAt(pos + 1);
 269         if (ch1 < '0' || ch1 > '9' || ch2 < '0' || ch2 > '9') {
 270             throw new DateTimeException("Zone offset ID '" + offsetId + "' is invalid: Non numeric characters found");
 271         }
 272         return (ch1 - 48) * 10 + (ch2 - 48);
 273     }
 274 
 275     //-----------------------------------------------------------------------
 276     /**
 277      * Obtains an instance of {@code ZoneOffset} using an offset in hours.
 278      *
 279      * @param hours  the time-zone offset in hours, from -18 to +18
 280      * @return the zone-offset, not null
 281      * @throws DateTimeException if the offset is not in the required range
 282      */
 283     public static ZoneOffset ofHours(int hours) {
 284         return ofHoursMinutesSeconds(hours, 0, 0);
 285     }
 286 
 287     /**
 288      * Obtains an instance of {@code ZoneOffset} using an offset in
 289      * hours and minutes.
 290      * <p>
 291      * The sign of the hours and minutes components must match.
 292      * Thus, if the hours is negative, the minutes must be negative or zero.
 293      * If the hours is zero, the minutes may be positive, negative or zero.
 294      *
 295      * @param hours  the time-zone offset in hours, from -18 to +18
 296      * @param minutes  the time-zone offset in minutes, from 0 to &plusmn;59, sign matches hours
 297      * @return the zone-offset, not null
 298      * @throws DateTimeException if the offset is not in the required range
 299      */
 300     public static ZoneOffset ofHoursMinutes(int hours, int minutes) {
 301         return ofHoursMinutesSeconds(hours, minutes, 0);
 302     }
 303 
 304     /**
 305      * Obtains an instance of {@code ZoneOffset} using an offset in
 306      * hours, minutes and seconds.
 307      * <p>
 308      * The sign of the hours, minutes and seconds components must match.
 309      * Thus, if the hours is negative, the minutes and seconds must be negative or zero.
 310      *
 311      * @param hours  the time-zone offset in hours, from -18 to +18
 312      * @param minutes  the time-zone offset in minutes, from 0 to &plusmn;59, sign matches hours and seconds
 313      * @param seconds  the time-zone offset in seconds, from 0 to &plusmn;59, sign matches hours and minutes
 314      * @return the zone-offset, not null
 315      * @throws DateTimeException if the offset is not in the required range
 316      */
 317     public static ZoneOffset ofHoursMinutesSeconds(int hours, int minutes, int seconds) {
 318         validate(hours, minutes, seconds);
 319         int totalSeconds = totalSeconds(hours, minutes, seconds);
 320         return ofTotalSeconds(totalSeconds);
 321     }
 322 
 323     //-----------------------------------------------------------------------
 324     /**
 325      * Obtains an instance of {@code ZoneOffset} from a temporal object.
 326      * <p>
 327      * A {@code TemporalAccessor} represents some form of date and time information.
 328      * This factory converts the arbitrary temporal object to an instance of {@code ZoneOffset}.
 329      * <p>
 330      * The conversion extracts the {@link ChronoField#OFFSET_SECONDS offset-seconds} field.
 331      * <p>
 332      * This method matches the signature of the functional interface {@link TemporalQuery}
 333      * allowing it to be used in queries via method reference, {@code ZoneOffset::from}.
 334      *
 335      * @param temporal  the temporal object to convert, not null
 336      * @return the zone-offset, not null
 337      * @throws DateTimeException if unable to convert to an {@code ZoneOffset}
 338      */
 339     public static ZoneOffset from(TemporalAccessor temporal) {
 340         if (temporal instanceof ZoneOffset) {
 341             return (ZoneOffset) temporal;
 342         }
 343         try {
 344             return ofTotalSeconds(temporal.get(OFFSET_SECONDS));
 345         } catch (DateTimeException ex) {
 346             throw new DateTimeException("Unable to obtain ZoneOffset from TemporalAccessor: " + temporal.getClass(), ex);
 347         }
 348     }
 349 
 350     //-----------------------------------------------------------------------
 351     /**
 352      * Validates the offset fields.
 353      *
 354      * @param hours  the time-zone offset in hours, from -18 to +18
 355      * @param minutes  the time-zone offset in minutes, from 0 to &plusmn;59
 356      * @param seconds  the time-zone offset in seconds, from 0 to &plusmn;59
 357      * @throws DateTimeException if the offset is not in the required range
 358      */
 359     private static void validate(int hours, int minutes, int seconds) {
 360         if (hours < -18 || hours > 18) {
 361             throw new DateTimeException("Zone offset hours not in valid range: value " + hours +
 362                     " is not in the range -18 to 18");
 363         }
 364         if (hours > 0) {
 365             if (minutes < 0 || seconds < 0) {
 366                 throw new DateTimeException("Zone offset minutes and seconds must be positive because hours is positive");
 367             }
 368         } else if (hours < 0) {
 369             if (minutes > 0 || seconds > 0) {
 370                 throw new DateTimeException("Zone offset minutes and seconds must be negative because hours is negative");
 371             }
 372         } else if ((minutes > 0 && seconds < 0) || (minutes < 0 && seconds > 0)) {
 373             throw new DateTimeException("Zone offset minutes and seconds must have the same sign");
 374         }
 375         if (Math.abs(minutes) > 59) {
 376             throw new DateTimeException("Zone offset minutes not in valid range: abs(value) " +
 377                     Math.abs(minutes) + " is not in the range 0 to 59");
 378         }
 379         if (Math.abs(seconds) > 59) {
 380             throw new DateTimeException("Zone offset seconds not in valid range: abs(value) " +
 381                     Math.abs(seconds) + " is not in the range 0 to 59");
 382         }
 383         if (Math.abs(hours) == 18 && (Math.abs(minutes) > 0 || Math.abs(seconds) > 0)) {
 384             throw new DateTimeException("Zone offset not in valid range: -18:00 to +18:00");
 385         }
 386     }
 387 
 388     /**
 389      * Calculates the total offset in seconds.
 390      *
 391      * @param hours  the time-zone offset in hours, from -18 to +18
 392      * @param minutes  the time-zone offset in minutes, from 0 to &plusmn;59, sign matches hours and seconds
 393      * @param seconds  the time-zone offset in seconds, from 0 to &plusmn;59, sign matches hours and minutes
 394      * @return the total in seconds
 395      */
 396     private static int totalSeconds(int hours, int minutes, int seconds) {
 397         return hours * SECONDS_PER_HOUR + minutes * SECONDS_PER_MINUTE + seconds;
 398     }
 399 
 400     //-----------------------------------------------------------------------
 401     /**
 402      * Obtains an instance of {@code ZoneOffset} specifying the total offset in seconds
 403      * <p>
 404      * The offset must be in the range {@code -18:00} to {@code +18:00}, which corresponds to -64800 to +64800.
 405      *
 406      * @param totalSeconds  the total time-zone offset in seconds, from -64800 to +64800
 407      * @return the ZoneOffset, not null
 408      * @throws DateTimeException if the offset is not in the required range
 409      */
 410     public static ZoneOffset ofTotalSeconds(int totalSeconds) {
 411         if (Math.abs(totalSeconds) > MAX_SECONDS) {
 412             throw new DateTimeException("Zone offset not in valid range: -18:00 to +18:00");
 413         }
 414         if (totalSeconds % (15 * SECONDS_PER_MINUTE) == 0) {
 415             Integer totalSecs = totalSeconds;
 416             ZoneOffset result = SECONDS_CACHE.get(totalSecs);
 417             if (result == null) {
 418                 result = new ZoneOffset(totalSeconds);
 419                 SECONDS_CACHE.putIfAbsent(totalSecs, result);
 420                 result = SECONDS_CACHE.get(totalSecs);
 421                 ID_CACHE.putIfAbsent(result.getId(), result);
 422             }
 423             return result;
 424         } else {
 425             return new ZoneOffset(totalSeconds);
 426         }
 427     }
 428 
 429     //-----------------------------------------------------------------------
 430     /**
 431      * Constructor.
 432      *
 433      * @param totalSeconds  the total time-zone offset in seconds, from -64800 to +64800
 434      */
 435     private ZoneOffset(int totalSeconds) {
 436         super();
 437         this.totalSeconds = totalSeconds;
 438         id = buildId(totalSeconds);
 439     }
 440 
 441     private static String buildId(int totalSeconds) {
 442         if (totalSeconds == 0) {
 443             return "Z";
 444         } else {
 445             int absTotalSeconds = Math.abs(totalSeconds);
 446             StringBuilder buf = new StringBuilder();
 447             int absHours = absTotalSeconds / SECONDS_PER_HOUR;
 448             int absMinutes = (absTotalSeconds / SECONDS_PER_MINUTE) % MINUTES_PER_HOUR;
 449             buf.append(totalSeconds < 0 ? "-" : "+")
 450                 .append(absHours < 10 ? "0" : "").append(absHours)
 451                 .append(absMinutes < 10 ? ":0" : ":").append(absMinutes);
 452             int absSeconds = absTotalSeconds % SECONDS_PER_MINUTE;
 453             if (absSeconds != 0) {
 454                 buf.append(absSeconds < 10 ? ":0" : ":").append(absSeconds);
 455             }
 456             return buf.toString();
 457         }
 458     }
 459 
 460     //-----------------------------------------------------------------------
 461     /**
 462      * Gets the total zone offset in seconds.
 463      * <p>
 464      * This is the primary way to access the offset amount.
 465      * It returns the total of the hours, minutes and seconds fields as a
 466      * single offset that can be added to a time.
 467      *
 468      * @return the total zone offset amount in seconds
 469      */
 470     public int getTotalSeconds() {
 471         return totalSeconds;
 472     }
 473 
 474     /**
 475      * Gets the normalized zone offset ID.
 476      * <p>
 477      * The ID is minor variation to the standard ISO-8601 formatted string
 478      * for the offset. There are three formats:
 479      * <p><ul>
 480      * <li>{@code Z} - for UTC (ISO-8601)
 481      * <li>{@code +hh:mm} or {@code -hh:mm} - if the seconds are zero (ISO-8601)
 482      * <li>{@code +hh:mm:ss} or {@code -hh:mm:ss} - if the seconds are non-zero (not ISO-8601)
 483      * </ul><p>
 484      *
 485      * @return the zone offset ID, not null
 486      */
 487     @Override
 488     public String getId() {
 489         return id;
 490     }
 491 
 492     /**
 493      * Gets the associated time-zone rules.
 494      * <p>
 495      * The rules will always return this offset when queried.
 496      * The implementation class is immutable, thread-safe and serializable.
 497      *
 498      * @return the rules, not null
 499      */
 500     @Override
 501     public ZoneRules getRules() {
 502         return ZoneRules.of(this);
 503     }
 504 
 505     //-----------------------------------------------------------------------
 506     /**
 507      * Checks if the specified field is supported.
 508      * <p>
 509      * This checks if this offset can be queried for the specified field.
 510      * If false, then calling the {@link #range(TemporalField) range} and
 511      * {@link #get(TemporalField) get} methods will throw an exception.
 512      * <p>
 513      * If the field is a {@link ChronoField} then the query is implemented here.
 514      * The {@code OFFSET_SECONDS} field returns true.
 515      * All other {@code ChronoField} instances will return false.
 516      * <p>
 517      * If the field is not a {@code ChronoField}, then the result of this method
 518      * is obtained by invoking {@code TemporalField.doIsSupported(TemporalAccessor)}
 519      * passing {@code this} as the argument.
 520      * Whether the field is supported is determined by the field.
 521      *
 522      * @param field  the field to check, null returns false
 523      * @return true if the field is supported on this offset, false if not
 524      */
 525     @Override
 526     public boolean isSupported(TemporalField field) {
 527         if (field instanceof ChronoField) {
 528             return field == OFFSET_SECONDS;
 529         }
 530         return field != null && field.doIsSupported(this);
 531     }
 532 
 533     /**
 534      * Gets the range of valid values for the specified field.
 535      * <p>
 536      * The range object expresses the minimum and maximum valid values for a field.
 537      * This offset is used to enhance the accuracy of the returned range.
 538      * If it is not possible to return the range, because the field is not supported
 539      * or for some other reason, an exception is thrown.
 540      * <p>
 541      * If the field is a {@link ChronoField} then the query is implemented here.
 542      * The {@link #isSupported(TemporalField) supported fields} will return
 543      * appropriate range instances.
 544      * All other {@code ChronoField} instances will throw a {@code DateTimeException}.
 545      * <p>
 546      * If the field is not a {@code ChronoField}, then the result of this method
 547      * is obtained by invoking {@code TemporalField.doRange(TemporalAccessor)}
 548      * passing {@code this} as the argument.
 549      * Whether the range can be obtained is determined by the field.
 550      *
 551      * @param field  the field to query the range for, not null
 552      * @return the range of valid values for the field, not null
 553      * @throws DateTimeException if the range for the field cannot be obtained
 554      */
 555     @Override  // override for Javadoc
 556     public ValueRange range(TemporalField field) {
 557         return TemporalAccessor.super.range(field);
 558     }
 559 
 560     /**
 561      * Gets the value of the specified field from this offset as an {@code int}.
 562      * <p>
 563      * This queries this offset for the value for the specified field.
 564      * The returned value will always be within the valid range of values for the field.
 565      * If it is not possible to return the value, because the field is not supported
 566      * or for some other reason, an exception is thrown.
 567      * <p>
 568      * If the field is a {@link ChronoField} then the query is implemented here.
 569      * The {@code OFFSET_SECONDS} field returns the value of the offset.
 570      * All other {@code ChronoField} instances will throw a {@code DateTimeException}.
 571      * <p>
 572      * If the field is not a {@code ChronoField}, then the result of this method
 573      * is obtained by invoking {@code TemporalField.doGet(TemporalAccessor)}
 574      * passing {@code this} as the argument. Whether the value can be obtained,
 575      * and what the value represents, is determined by the field.
 576      *
 577      * @param field  the field to get, not null
 578      * @return the value for the field
 579      * @throws DateTimeException if a value for the field cannot be obtained
 580      * @throws ArithmeticException if numeric overflow occurs
 581      */
 582     @Override  // override for Javadoc and performance
 583     public int get(TemporalField field) {
 584         if (field == OFFSET_SECONDS) {
 585             return totalSeconds;
 586         } else if (field instanceof ChronoField) {
 587             throw new DateTimeException("Unsupported field: " + field.getName());
 588         }
 589         return range(field).checkValidIntValue(getLong(field), field);
 590     }
 591 
 592     /**
 593      * Gets the value of the specified field from this offset as a {@code long}.
 594      * <p>
 595      * This queries this offset for the value for the specified field.
 596      * If it is not possible to return the value, because the field is not supported
 597      * or for some other reason, an exception is thrown.
 598      * <p>
 599      * If the field is a {@link ChronoField} then the query is implemented here.
 600      * The {@code OFFSET_SECONDS} field returns the value of the offset.
 601      * All other {@code ChronoField} instances will throw a {@code DateTimeException}.
 602      * <p>
 603      * If the field is not a {@code ChronoField}, then the result of this method
 604      * is obtained by invoking {@code TemporalField.doGet(TemporalAccessor)}
 605      * passing {@code this} as the argument. Whether the value can be obtained,
 606      * and what the value represents, is determined by the field.
 607      *
 608      * @param field  the field to get, not null
 609      * @return the value for the field
 610      * @throws DateTimeException if a value for the field cannot be obtained
 611      * @throws ArithmeticException if numeric overflow occurs
 612      */
 613     @Override
 614     public long getLong(TemporalField field) {
 615         if (field == OFFSET_SECONDS) {
 616             return totalSeconds;
 617         } else if (field instanceof ChronoField) {
 618             throw new DateTimeException("Unsupported field: " + field.getName());
 619         }
 620         return field.doGet(this);
 621     }
 622 
 623     //-----------------------------------------------------------------------
 624     /**
 625      * Queries this offset using the specified query.
 626      * <p>
 627      * This queries this offset using the specified query strategy object.
 628      * The {@code TemporalQuery} object defines the logic to be used to
 629      * obtain the result. Read the documentation of the query to understand
 630      * what the result of this method will be.
 631      * <p>
 632      * The result of this method is obtained by invoking the
 633      * {@link TemporalQuery#queryFrom(TemporalAccessor)} method on the
 634      * specified query passing {@code this} as the argument.
 635      *
 636      * @param <R> the type of the result
 637      * @param query  the query to invoke, not null
 638      * @return the query result, null may be returned (defined by the query)
 639      * @throws DateTimeException if unable to query (defined by the query)
 640      * @throws ArithmeticException if numeric overflow occurs (defined by the query)
 641      */
 642     @SuppressWarnings("unchecked")
 643     @Override
 644     public <R> R query(TemporalQuery<R> query) {
 645         if (query == Queries.offset() || query == Queries.zone()) {
 646             return (R) this;
 647         }
 648         return TemporalAccessor.super.query(query);
 649     }
 650 
 651     /**
 652      * Adjusts the specified temporal object to have the same offset as this object.
 653      * <p>
 654      * This returns a temporal object of the same observable type as the input
 655      * with the offset changed to be the same as this.
 656      * <p>
 657      * The adjustment is equivalent to using {@link Temporal#with(TemporalField, long)}
 658      * passing {@link ChronoField#OFFSET_SECONDS} as the field.
 659      * <p>
 660      * In most cases, it is clearer to reverse the calling pattern by using
 661      * {@link Temporal#with(TemporalAdjuster)}:
 662      * <pre>
 663      *   // these two lines are equivalent, but the second approach is recommended
 664      *   temporal = thisOffset.adjustInto(temporal);
 665      *   temporal = temporal.with(thisOffset);
 666      * </pre>
 667      * <p>
 668      * This instance is immutable and unaffected by this method call.
 669      *
 670      * @param temporal  the target object to be adjusted, not null
 671      * @return the adjusted object, not null
 672      * @throws DateTimeException if unable to make the adjustment
 673      * @throws ArithmeticException if numeric overflow occurs
 674      */
 675     @Override
 676     public Temporal adjustInto(Temporal temporal) {
 677         return temporal.with(OFFSET_SECONDS, totalSeconds);
 678     }
 679 
 680     //-----------------------------------------------------------------------
 681     /**
 682      * Compares this offset to another offset in descending order.
 683      * <p>
 684      * The offsets are compared in the order that they occur for the same time
 685      * of day around the world. Thus, an offset of {@code +10:00} comes before an
 686      * offset of {@code +09:00} and so on down to {@code -18:00}.
 687      * <p>
 688      * The comparison is "consistent with equals", as defined by {@link Comparable}.
 689      *
 690      * @param other  the other date to compare to, not null
 691      * @return the comparator value, negative if less, postive if greater
 692      * @throws NullPointerException if {@code other} is null
 693      */
 694     @Override
 695     public int compareTo(ZoneOffset other) {
 696         return other.totalSeconds - totalSeconds;
 697     }
 698 
 699     //-----------------------------------------------------------------------
 700     /**
 701      * Checks if this offset is equal to another offset.
 702      * <p>
 703      * The comparison is based on the amount of the offset in seconds.
 704      * This is equivalent to a comparison by ID.
 705      *
 706      * @param obj  the object to check, null returns false
 707      * @return true if this is equal to the other offset
 708      */
 709     @Override
 710     public boolean equals(Object obj) {
 711         if (this == obj) {
 712            return true;
 713         }
 714         if (obj instanceof ZoneOffset) {
 715             return totalSeconds == ((ZoneOffset) obj).totalSeconds;
 716         }
 717         return false;
 718     }
 719 
 720     /**
 721      * A hash code for this offset.
 722      *
 723      * @return a suitable hash code
 724      */
 725     @Override
 726     public int hashCode() {
 727         return totalSeconds;
 728     }
 729 
 730     //-----------------------------------------------------------------------
 731     /**
 732      * Outputs this offset as a {@code String}, using the normalized ID.
 733      *
 734      * @return a string representation of this offset, not null
 735      */
 736     @Override
 737     public String toString() {
 738         return id;
 739     }
 740 
 741     // -----------------------------------------------------------------------
 742     /**
 743      * Writes the object using a
 744      * <a href="../../serialized-form.html#java.time.Ser">dedicated serialized form</a>.
 745      * <pre>
 746      *  out.writeByte(8);  // identifies this as a ZoneOffset
 747      *  int offsetByte = totalSeconds % 900 == 0 ? totalSeconds / 900 : 127;
 748      *  out.writeByte(offsetByte);
 749      *  if (offsetByte == 127) {
 750      *    out.writeInt(totalSeconds);
 751      *  }
 752      * </pre>
 753      *
 754      * @return the instance of {@code Ser}, not null
 755      */
 756     private Object writeReplace() {
 757         return new Ser(Ser.ZONE_OFFSET_TYPE, this);
 758     }
 759 
 760     /**
 761      * Defend against malicious streams.
 762      * @return never
 763      * @throws InvalidObjectException always
 764      */
 765     private Object readResolve() throws ObjectStreamException {
 766         throw new InvalidObjectException("Deserialization via serialization delegate");
 767     }
 768 
 769     @Override
 770     void write(DataOutput out) throws IOException {
 771         out.writeByte(Ser.ZONE_OFFSET_TYPE);
 772         writeExternal(out);
 773     }
 774 
 775     void writeExternal(DataOutput out) throws IOException {
 776         final int offsetSecs = totalSeconds;
 777         int offsetByte = offsetSecs % 900 == 0 ? offsetSecs / 900 : 127;  // compress to -72 to +72
 778         out.writeByte(offsetByte);
 779         if (offsetByte == 127) {
 780             out.writeInt(offsetSecs);
 781         }
 782     }
 783 
 784     static ZoneOffset readExternal(DataInput in) throws IOException {
 785         int offsetByte = in.readByte();
 786         return (offsetByte == 127 ? ZoneOffset.ofTotalSeconds(in.readInt()) : ZoneOffset.ofTotalSeconds(offsetByte * 900));
 787     }
 788 
 789 }