content: /*
   * Copyright (c) 2012, 2015, Oracle and/or its affiliates. All rights reserved.
   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   *
   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.  Oracle designates this
   * particular file as subject to the "Classpath" exception as provided
   * by Oracle in the LICENSE file that accompanied this code.
   *
   * This code is distributed in the hope that it will be useful, but WITHOUT
   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   * version 2 for more details (a copy is included in the LICENSE file that
   * accompanied this code).
   *
   * You should have received a copy of the GNU General Public License version
   * 2 along with this work; if not, write to the Free Software Foundation,
   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
   * or visit www.oracle.com if you need additional information or have any
   * questions.
   */
  
  /*
   * This file is available under and governed by the GNU General Public
   * License version 2 only, as published by the Free Software Foundation.
   * However, the following notice accompanied the original version of this
   * file:
   *
   * Copyright (c) 2007-2012, Stephen Colebourne & Michael Nascimento Santos
   *
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions are met:
   *
   *  * Redistributions of source code must retain the above copyright notice,
   *    this list of conditions and the following disclaimer.
   *
   *  * Redistributions in binary form must reproduce the above copyright notice,
   *    this list of conditions and the following disclaimer in the documentation
   *    and/or other materials provided with the distribution.
   *
   *  * Neither the name of JSR-310 nor the names of its contributors
   *    may be used to endorse or promote products derived from this software
   *    without specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
   * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
   * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
   * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
   * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
   * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
   * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
   * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
   * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   */
  package java.time;
  
  import static java.time.LocalTime.NANOS_PER_SECOND;
  import static java.time.LocalTime.SECONDS_PER_DAY;
  import static java.time.LocalTime.SECONDS_PER_HOUR;
  import static java.time.LocalTime.SECONDS_PER_MINUTE;
  import static java.time.temporal.ChronoField.INSTANT_SECONDS;
  import static java.time.temporal.ChronoField.MICRO_OF_SECOND;
  import static java.time.temporal.ChronoField.MILLI_OF_SECOND;
  import static java.time.temporal.ChronoField.NANO_OF_SECOND;
  import static java.time.temporal.ChronoUnit.DAYS;
  import static java.time.temporal.ChronoUnit.NANOS;
  
  import java.io.DataInput;
  import java.io.DataOutput;
  import java.io.IOException;
  import java.io.InvalidObjectException;
  import java.io.ObjectInputStream;
  import java.io.Serializable;
  import java.time.format.DateTimeFormatter;
  import java.time.format.DateTimeParseException;
  import java.time.temporal.ChronoField;
  import java.time.temporal.ChronoUnit;
  import java.time.temporal.Temporal;
  import java.time.temporal.TemporalAccessor;
  import java.time.temporal.TemporalAdjuster;
  import java.time.temporal.TemporalAmount;
  import java.time.temporal.TemporalField;
  import java.time.temporal.TemporalQueries;
  import java.time.temporal.TemporalQuery;
  import java.time.temporal.TemporalUnit;
  import java.time.temporal.UnsupportedTemporalTypeException;
  import java.time.temporal.ValueRange;
  import java.util.Objects;
  
  // Android-changed: removed ValueBased paragraph.
  
  /**
   * An instantaneous point on the time-line.
   * <p>
   * This class models a single instantaneous point on the time-line.
   * This might be used to record event time-stamps in the application.
   * <p>
   * The range of an instant requires the storage of a number larger than a {@code long}.
   * To achieve this, the class stores a {@code long} representing epoch-seconds and an
   * {@code int} representing nanosecond-of-second, which will always be between 0 and 999,999,999.
   * The epoch-seconds are measured from the standard Java epoch of {@code 1970-01-01T00:00:00Z}
   * where instants after the epoch have positive values, and earlier instants have negative values.
   * For both the epoch-second and nanosecond parts, a larger value is always later on the time-line
   * than a smaller value.
   *
   * <h3>Time-scale</h3>
   * <p>
   * The length of the solar day is the standard way that humans measure time.
   * This has traditionally been subdivided into 24 hours of 60 minutes of 60 seconds,
   * forming a 86400 second day.
   * <p>
   * Modern timekeeping is based on atomic clocks which precisely define an SI second
   * relative to the transitions of a Caesium atom. The length of an SI second was defined
   * to be very close to the 86400th fraction of a day.
   * <p>
   * Unfortunately, as the Earth rotates the length of the day varies.
   * In addition, over time the average length of the day is getting longer as the Earth slows.
   * As a result, the length of a solar day in 2012 is slightly longer than 86400 SI seconds.
   * The actual length of any given day and the amount by which the Earth is slowing
   * are not predictable and can only be determined by measurement.
   * The UT1 time-scale captures the accurate length of day, but is only available some
   * time after the day has completed.
   * <p>
   * The UTC time-scale is a standard approach to bundle up all the additional fractions
   * of a second from UT1 into whole seconds, known as <i>leap-seconds</i>.
   * A leap-second may be added or removed depending on the Earth's rotational changes.
   * As such, UTC permits a day to have 86399 SI seconds or 86401 SI seconds where
   * necessary in order to keep the day aligned with the Sun.
   * <p>
   * The modern UTC time-scale was introduced in 1972, introducing the concept of whole leap-seconds.
   * Between 1958 and 1972, the definition of UTC was complex, with minor sub-second leaps and
   * alterations to the length of the notional second. As of 2012, discussions are underway
   * to change the definition of UTC again, with the potential to remove leap seconds or
   * introduce other changes.
   * <p>
   * Given the complexity of accurate timekeeping described above, this Java API defines
   * its own time-scale, the <i>Java Time-Scale</i>.
   * <p>
   * The Java Time-Scale divides each calendar day into exactly 86400
   * subdivisions, known as seconds.  These seconds may differ from the
   * SI second.  It closely matches the de facto international civil time
   * scale, the definition of which changes from time to time.
   * <p>
   * The Java Time-Scale has slightly different definitions for different
   * segments of the time-line, each based on the consensus international
   * time scale that is used as the basis for civil time. Whenever the
   * internationally-agreed time scale is modified or replaced, a new
   * segment of the Java Time-Scale must be defined for it.  Each segment
   * must meet these requirements:
   * <ul>
   * <li>the Java Time-Scale shall closely match the underlying international
   *  civil time scale;</li>
   * <li>the Java Time-Scale shall exactly match the international civil
   *  time scale at noon each day;</li>
   * <li>the Java Time-Scale shall have a precisely-defined relationship to
   *  the international civil time scale.</li>
   * </ul>
   * There are currently, as of 2013, two segments in the Java time-scale.
   * <p>
   * For the segment from 1972-11-03 (exact boundary discussed below) until
   * further notice, the consensus international time scale is UTC (with
   * leap seconds).  In this segment, the Java Time-Scale is identical to
   * <a href="http://www.cl.cam.ac.uk/~mgk25/time/utc-sls/">UTC-SLS</a>.
   * This is identical to UTC on days that do not have a leap second.
   * On days that do have a leap second, the leap second is spread equally
   * over the last 1000 seconds of the day, maintaining the appearance of
   * exactly 86400 seconds per day.
   * <p>
   * For the segment prior to 1972-11-03, extending back arbitrarily far,
   * the consensus international time scale is defined to be UT1, applied
   * proleptically, which is equivalent to the (mean) solar time on the
   * prime meridian (Greenwich). In this segment, the Java Time-Scale is
   * identical to the consensus international time scale. The exact
   * boundary between the two segments is the instant where UT1 = UTC
   * between 1972-11-03T00:00 and 1972-11-04T12:00.
   * <p>
   * Implementations of the Java time-scale using the JSR-310 API are not
   * required to provide any clock that is sub-second accurate, or that
   * progresses monotonically or smoothly. Implementations are therefore
   * not required to actually perform the UTC-SLS slew or to otherwise be
   * aware of leap seconds. JSR-310 does, however, require that
   * implementations must document the approach they use when defining a
   * clock representing the current instant.
   * See {@link Clock} for details on the available clocks.
   * <p>
   * The Java time-scale is used for all date-time classes.
   * This includes {@code Instant}, {@code LocalDate}, {@code LocalTime}, {@code OffsetDateTime},
   * {@code ZonedDateTime} and {@code Duration}.
   *
   * @implSpec
   * This class is immutable and thread-safe.
   *
   * @since 1.8
   */
  public final class Instant
          implements Temporal, TemporalAdjuster, Comparable<Instant>, Serializable {
  
      /**
       * Constant for the 1970-01-01T00:00:00Z epoch instant.
       */
      public static final Instant EPOCH = new Instant(0, 0);
      /**
       * The minimum supported epoch second.
       */
      private static final long MIN_SECOND = -31557014167219200L;
      /**
       * The maximum supported epoch second.
       */
      private static final long MAX_SECOND = 31556889864403199L;
      /**
       * The minimum supported {@code Instant}, '-1000000000-01-01T00:00Z'.
       * This could be used by an application as a "far past" instant.
       * <p>
       * This is one year earlier than the minimum {@code LocalDateTime}.
       * This provides sufficient values to handle the range of {@code ZoneOffset}
       * which affect the instant in addition to the local date-time.
       * The value is also chosen such that the value of the year fits in
       * an {@code int}.
       */
      public static final Instant MIN = Instant.ofEpochSecond(MIN_SECOND, 0);
      /**
       * The maximum supported {@code Instant}, '1000000000-12-31T23:59:59.999999999Z'.
       * This could be used by an application as a "far future" instant.
       * <p>
       * This is one year later than the maximum {@code LocalDateTime}.
       * This provides sufficient values to handle the range of {@code ZoneOffset}
       * which affect the instant in addition to the local date-time.
       * The value is also chosen such that the value of the year fits in
       * an {@code int}.
       */
      public static final Instant MAX = Instant.ofEpochSecond(MAX_SECOND, 999_999_999);
  
      /**
       * Serialization version.
       */
      private static final long serialVersionUID = -665713676816604388L;
  
      /**
       * The number of seconds from the epoch of 1970-01-01T00:00:00Z.
       */
      private final long seconds;
      /**
       * The number of nanoseconds, later along the time-line, from the seconds field.
       * This is always positive, and never exceeds 999,999,999.
       */
      private final int nanos;
  
      //-----------------------------------------------------------------------
      /**
       * Obtains the current instant from the system clock.
       * <p>
       * This will query the {@link Clock#systemUTC() system UTC clock} to
       * obtain the current instant.
       * <p>
       * Using this method will prevent the ability to use an alternate time-source for
       * testing because the clock is effectively hard-coded.
       *
       * @return the current instant using the system clock, not null
       */
      public static Instant now() {
          return Clock.systemUTC().instant();
      }
  
      /**
       * Obtains the current instant from the specified clock.
       * <p>
       * This will query the specified clock to obtain the current time.
       * <p>
       * Using this method allows the use of an alternate clock for testing.
       * The alternate clock may be introduced using {@link Clock dependency injection}.
       *
       * @param clock  the clock to use, not null
       * @return the current instant, not null
       */
      public static Instant now(Clock clock) {
          Objects.requireNonNull(clock, "clock");
          return clock.instant();
      }
  
      //-----------------------------------------------------------------------
      /**
       * Obtains an instance of {@code Instant} using seconds from the
       * epoch of 1970-01-01T00:00:00Z.
       * <p>
       * The nanosecond field is set to zero.
       *
       * @param epochSecond  the number of seconds from 1970-01-01T00:00:00Z
       * @return an instant, not null
       * @throws DateTimeException if the instant exceeds the maximum or minimum instant
       */
      public static Instant ofEpochSecond(long epochSecond) {
          return create(epochSecond, 0);
      }
  
      /**
       * Obtains an instance of {@code Instant} using seconds from the
       * epoch of 1970-01-01T00:00:00Z and nanosecond fraction of second.
       * <p>
       * This method allows an arbitrary number of nanoseconds to be passed in.
       * The factory will alter the values of the second and nanosecond in order
       * to ensure that the stored nanosecond is in the range 0 to 999,999,999.
       * For example, the following will result in the exactly the same instant:
       * <pre>
       *  Instant.ofEpochSecond(3, 1);
       *  Instant.ofEpochSecond(4, -999_999_999);
       *  Instant.ofEpochSecond(2, 1000_000_001);
       * </pre>
       *
       * @param epochSecond  the number of seconds from 1970-01-01T00:00:00Z
       * @param nanoAdjustment  the nanosecond adjustment to the number of seconds, positive or negative
       * @return an instant, not null
       * @throws DateTimeException if the instant exceeds the maximum or minimum instant
       * @throws ArithmeticException if numeric overflow occurs
       */
      public static Instant ofEpochSecond(long epochSecond, long nanoAdjustment) {
          long secs = Math.addExact(epochSecond, Math.floorDiv(nanoAdjustment, NANOS_PER_SECOND));
          int nos = (int)Math.floorMod(nanoAdjustment, NANOS_PER_SECOND);
          return create(secs, nos);
      }
  
      /**
       * Obtains an instance of {@code Instant} using milliseconds from the
       * epoch of 1970-01-01T00:00:00Z.
       * <p>
       * The seconds and nanoseconds are extracted from the specified milliseconds.
       *
       * @param epochMilli  the number of milliseconds from 1970-01-01T00:00:00Z
       * @return an instant, not null
       * @throws DateTimeException if the instant exceeds the maximum or minimum instant
       */
      public static Instant ofEpochMilli(long epochMilli) {
          long secs = Math.floorDiv(epochMilli, 1000);
          int mos = (int)Math.floorMod(epochMilli, 1000);
          return create(secs, mos * 1000_000);
      }
  
      //-----------------------------------------------------------------------
      /**
       * Obtains an instance of {@code Instant} from a temporal object.
       * <p>
       * This obtains an instant based on the specified temporal.
       * A {@code TemporalAccessor} represents an arbitrary set of date and time information,
       * which this factory converts to an instance of {@code Instant}.
       * <p>
       * The conversion extracts the {@link ChronoField#INSTANT_SECONDS INSTANT_SECONDS}
       * and {@link ChronoField#NANO_OF_SECOND NANO_OF_SECOND} fields.
       * <p>
       * This method matches the signature of the functional interface {@link TemporalQuery}
       * allowing it to be used as a query via method reference, {@code Instant::from}.
       *
       * @param temporal  the temporal object to convert, not null
       * @return the instant, not null
       * @throws DateTimeException if unable to convert to an {@code Instant}
       */
      public static Instant from(TemporalAccessor temporal) {
          if (temporal instanceof Instant) {
              return (Instant) temporal;
          }
          Objects.requireNonNull(temporal, "temporal");
          try {
              long instantSecs = temporal.getLong(INSTANT_SECONDS);
              int nanoOfSecond = temporal.get(NANO_OF_SECOND);
              return Instant.ofEpochSecond(instantSecs, nanoOfSecond);
          } catch (DateTimeException ex) {
              throw new DateTimeException("Unable to obtain Instant from TemporalAccessor: " +
                      temporal + " of type " + temporal.getClass().getName(), ex);
          }
      }
  
      //-----------------------------------------------------------------------
      /**
       * Obtains an instance of {@code Instant} from a text string such as
       * {@code 2007-12-03T10:15:30.00Z}.
       * <p>
       * The string must represent a valid instant in UTC and is parsed using
       * {@link DateTimeFormatter#ISO_INSTANT}.
       *
       * @param text  the text to parse, not null
       * @return the parsed instant, not null
       * @throws DateTimeParseException if the text cannot be parsed
       */
      public static Instant parse(final CharSequence text) {
          return DateTimeFormatter.ISO_INSTANT.parse(text, Instant::from);
      }
  
      //-----------------------------------------------------------------------
      /**
       * Obtains an instance of {@code Instant} using seconds and nanoseconds.
       *
       * @param seconds  the length of the duration in seconds
       * @param nanoOfSecond  the nano-of-second, from 0 to 999,999,999
       * @throws DateTimeException if the instant exceeds the maximum or minimum instant
       */
      private static Instant create(long seconds, int nanoOfSecond) {
          if ((seconds | nanoOfSecond) == 0) {
              return EPOCH;
          }
          if (seconds < MIN_SECOND || seconds > MAX_SECOND) {
              throw new DateTimeException("Instant exceeds minimum or maximum instant");
          }
          return new Instant(seconds, nanoOfSecond);
      }
  
      /**
       * Constructs an instance of {@code Instant} using seconds from the epoch of
       * 1970-01-01T00:00:00Z and nanosecond fraction of second.
       *
       * @param epochSecond  the number of seconds from 1970-01-01T00:00:00Z
       * @param nanos  the nanoseconds within the second, must be positive
       */
      private Instant(long epochSecond, int nanos) {
          super();
          this.seconds = epochSecond;
          this.nanos = nanos;
      }
  
      //-----------------------------------------------------------------------
      /**
       * Checks if the specified field is supported.
       * <p>
       * This checks if this instant can be queried for the specified field.
       * If false, then calling the {@link #range(TemporalField) range},
       * {@link #get(TemporalField) get} and {@link #with(TemporalField, long)}
       * methods will throw an exception.
       * <p>
       * If the field is a {@link ChronoField} then the query is implemented here.
       * The supported fields are:
       * <ul>
       * <li>{@code NANO_OF_SECOND}
       * <li>{@code MICRO_OF_SECOND}
       * <li>{@code MILLI_OF_SECOND}
       * <li>{@code INSTANT_SECONDS}
       * </ul>
       * All other {@code ChronoField} instances will return false.
       * <p>
       * If the field is not a {@code ChronoField}, then the result of this method
       * is obtained by invoking {@code TemporalField.isSupportedBy(TemporalAccessor)}
       * passing {@code this} as the argument.
       * Whether the field is supported is determined by the field.
       *
       * @param field  the field to check, null returns false
       * @return true if the field is supported on this instant, false if not
       */
      @Override
      public boolean isSupported(TemporalField field) {
          if (field instanceof ChronoField) {
              return field == INSTANT_SECONDS || field == NANO_OF_SECOND || field == MICRO_OF_SECOND || field == MILLI_OF_SECOND;
          }
          return field != null && field.isSupportedBy(this);
      }
  
      /**
       * Checks if the specified unit is supported.
       * <p>
       * This checks if the specified unit can be added to, or subtracted from, this date-time.
       * If false, then calling the {@link #plus(long, TemporalUnit)} and
       * {@link #minus(long, TemporalUnit) minus} methods will throw an exception.
       * <p>
       * If the unit is a {@link ChronoUnit} then the query is implemented here.
       * The supported units are:
       * <ul>
       * <li>{@code NANOS}
       * <li>{@code MICROS}
       * <li>{@code MILLIS}
       * <li>{@code SECONDS}
       * <li>{@code MINUTES}
       * <li>{@code HOURS}
       * <li>{@code HALF_DAYS}
       * <li>{@code DAYS}
       * </ul>
       * All other {@code ChronoUnit} instances will return false.
       * <p>
       * If the unit is not a {@code ChronoUnit}, then the result of this method
       * is obtained by invoking {@code TemporalUnit.isSupportedBy(Temporal)}
       * passing {@code this} as the argument.
       * Whether the unit is supported is determined by the unit.
       *
       * @param unit  the unit to check, null returns false
       * @return true if the unit can be added/subtracted, false if not
       */
      @Override
      public boolean isSupported(TemporalUnit unit) {
          if (unit instanceof ChronoUnit) {
              return unit.isTimeBased() || unit == DAYS;
          }
          return unit != null && unit.isSupportedBy(this);
      }
  
      //-----------------------------------------------------------------------
      /**
       * Gets the range of valid values for the specified field.
       * <p>
       * The range object expresses the minimum and maximum valid values for a field.
       * This instant is used to enhance the accuracy of the returned range.
       * If it is not possible to return the range, because the field is not supported
       * or for some other reason, an exception is thrown.
       * <p>
       * If the field is a {@link ChronoField} then the query is implemented here.
       * The {@link #isSupported(TemporalField) supported fields} will return
       * appropriate range instances.
       * All other {@code ChronoField} instances will throw an {@code UnsupportedTemporalTypeException}.
       * <p>
       * If the field is not a {@code ChronoField}, then the result of this method
       * is obtained by invoking {@code TemporalField.rangeRefinedBy(TemporalAccessor)}
       * passing {@code this} as the argument.
       * Whether the range can be obtained is determined by the field.
       *
       * @param field  the field to query the range for, not null
       * @return the range of valid values for the field, not null
       * @throws DateTimeException if the range for the field cannot be obtained
       * @throws UnsupportedTemporalTypeException if the field is not supported
       */
      @Override  // override for Javadoc
      public ValueRange range(TemporalField field) {
          return Temporal.super.range(field);
      }
  
      /**
       * Gets the value of the specified field from this instant as an {@code int}.
       * <p>
       * This queries this instant for the value of the specified field.
       * The returned value will always be within the valid range of values for the field.
       * If it is not possible to return the value, because the field is not supported
       * or for some other reason, an exception is thrown.
       * <p>
       * If the field is a {@link ChronoField} then the query is implemented here.
       * The {@link #isSupported(TemporalField) supported fields} will return valid
       * values based on this date-time, except {@code INSTANT_SECONDS} which is too
       * large to fit in an {@code int} and throws a {@code DateTimeException}.
       * All other {@code ChronoField} instances will throw an {@code UnsupportedTemporalTypeException}.
       * <p>
       * If the field is not a {@code ChronoField}, then the result of this method
       * is obtained by invoking {@code TemporalField.getFrom(TemporalAccessor)}
       * passing {@code this} as the argument. Whether the value can be obtained,
       * and what the value represents, is determined by the field.
       *
       * @param field  the field to get, not null
       * @return the value for the field
       * @throws DateTimeException if a value for the field cannot be obtained or
       *         the value is outside the range of valid values for the field
       * @throws UnsupportedTemporalTypeException if the field is not supported or
       *         the range of values exceeds an {@code int}
       * @throws ArithmeticException if numeric overflow occurs
       */
      @Override  // override for Javadoc and performance
      public int get(TemporalField field) {
          if (field instanceof ChronoField) {
              switch ((ChronoField) field) {
                  case NANO_OF_SECOND: return nanos;
                  case MICRO_OF_SECOND: return nanos / 1000;
                  case MILLI_OF_SECOND: return nanos / 1000_000;
                  case INSTANT_SECONDS: INSTANT_SECONDS.checkValidIntValue(seconds);
              }
              throw new UnsupportedTemporalTypeException("Unsupported field: " + field);
          }
          return range(field).checkValidIntValue(field.getFrom(this), field);
      }
  
      /**
       * Gets the value of the specified field from this instant as a {@code long}.
       * <p>
       * This queries this instant for the value of the specified field.
       * If it is not possible to return the value, because the field is not supported
       * or for some other reason, an exception is thrown.
       * <p>
       * If the field is a {@link ChronoField} then the query is implemented here.
       * The {@link #isSupported(TemporalField) supported fields} will return valid
       * values based on this date-time.
       * All other {@code ChronoField} instances will throw an {@code UnsupportedTemporalTypeException}.
       * <p>
       * If the field is not a {@code ChronoField}, then the result of this method
       * is obtained by invoking {@code TemporalField.getFrom(TemporalAccessor)}
       * passing {@code this} as the argument. Whether the value can be obtained,
       * and what the value represents, is determined by the field.
       *
       * @param field  the field to get, not null
       * @return the value for the field
       * @throws DateTimeException if a value for the field cannot be obtained
       * @throws UnsupportedTemporalTypeException if the field is not supported
       * @throws ArithmeticException if numeric overflow occurs
       */
      @Override
      public long getLong(TemporalField field) {
          if (field instanceof ChronoField) {
              switch ((ChronoField) field) {
                  case NANO_OF_SECOND: return nanos;
                  case MICRO_OF_SECOND: return nanos / 1000;
                  case MILLI_OF_SECOND: return nanos / 1000_000;
                  case INSTANT_SECONDS: return seconds;
              }
              throw new UnsupportedTemporalTypeException("Unsupported field: " + field);
          }
          return field.getFrom(this);
      }
  
      //-----------------------------------------------------------------------
      /**
       * Gets the number of seconds from the Java epoch of 1970-01-01T00:00:00Z.
       * <p>
       * The epoch second count is a simple incrementing count of seconds where
       * second 0 is 1970-01-01T00:00:00Z.
       * The nanosecond part of the day is returned by {@code getNanosOfSecond}.
       *
       * @return the seconds from the epoch of 1970-01-01T00:00:00Z
       */
      public long getEpochSecond() {
          return seconds;
      }
  
      /**
       * Gets the number of nanoseconds, later along the time-line, from the start
       * of the second.
       * <p>
       * The nanosecond-of-second value measures the total number of nanoseconds from
       * the second returned by {@code getEpochSecond}.
       *
       * @return the nanoseconds within the second, always positive, never exceeds 999,999,999
       */
      public int getNano() {
          return nanos;
      }
  
      //-------------------------------------------------------------------------
      /**
       * Returns an adjusted copy of this instant.
       * <p>
       * This returns an {@code Instant}, based on this one, with the instant adjusted.
       * The adjustment takes place using the specified adjuster strategy object.
       * Read the documentation of the adjuster to understand what adjustment will be made.
       * <p>
       * The result of this method is obtained by invoking the
       * {@link TemporalAdjuster#adjustInto(Temporal)} method on the
       * specified adjuster passing {@code this} as the argument.
       * <p>
       * This instance is immutable and unaffected by this method call.
       *
       * @param adjuster the adjuster to use, not null
       * @return an {@code Instant} based on {@code this} with the adjustment made, not null
       * @throws DateTimeException if the adjustment cannot be made
       * @throws ArithmeticException if numeric overflow occurs
       */
      @Override
      public Instant with(TemporalAdjuster adjuster) {
          return (Instant) adjuster.adjustInto(this);
      }
  
      /**
       * Returns a copy of this instant with the specified field set to a new value.
       * <p>
       * This returns an {@code Instant}, based on this one, with the value
       * for the specified field changed.
       * If it is not possible to set the value, because the field is not supported or for
       * some other reason, an exception is thrown.
       * <p>
       * If the field is a {@link ChronoField} then the adjustment is implemented here.
       * The supported fields behave as follows:
       * <ul>
       * <li>{@code NANO_OF_SECOND} -
       *  Returns an {@code Instant} with the specified nano-of-second.
       *  The epoch-second will be unchanged.
       * <li>{@code MICRO_OF_SECOND} -
       *  Returns an {@code Instant} with the nano-of-second replaced by the specified
       *  micro-of-second multiplied by 1,000. The epoch-second will be unchanged.
       * <li>{@code MILLI_OF_SECOND} -
       *  Returns an {@code Instant} with the nano-of-second replaced by the specified
       *  milli-of-second multiplied by 1,000,000. The epoch-second will be unchanged.
       * <li>{@code INSTANT_SECONDS} -
       *  Returns an {@code Instant} with the specified epoch-second.
       *  The nano-of-second will be unchanged.
       * </ul>
       * <p>
       * In all cases, if the new value is outside the valid range of values for the field
       * then a {@code DateTimeException} will be thrown.
       * <p>
       * All other {@code ChronoField} instances will throw an {@code UnsupportedTemporalTypeException}.
       * <p>
       * If the field is not a {@code ChronoField}, then the result of this method
       * is obtained by invoking {@code TemporalField.adjustInto(Temporal, long)}
       * passing {@code this} as the argument. In this case, the field determines
       * whether and how to adjust the instant.
       * <p>
       * This instance is immutable and unaffected by this method call.
       *
       * @param field  the field to set in the result, not null
       * @param newValue  the new value of the field in the result
       * @return an {@code Instant} based on {@code this} with the specified field set, not null
       * @throws DateTimeException if the field cannot be set
       * @throws UnsupportedTemporalTypeException if the field is not supported
       * @throws ArithmeticException if numeric overflow occurs
       */
      @Override
      public Instant with(TemporalField field, long newValue) {
          if (field instanceof ChronoField) {
              ChronoField f = (ChronoField) field;
              f.checkValidValue(newValue);
              switch (f) {
                  case MILLI_OF_SECOND: {
                      int nval = (int) newValue * 1000_000;
                      return (nval != nanos ? create(seconds, nval) : this);
                  }
                  case MICRO_OF_SECOND: {
                      int nval = (int) newValue * 1000;
                      return (nval != nanos ? create(seconds, nval) : this);
                  }
                  case NANO_OF_SECOND: return (newValue != nanos ? create(seconds, (int) newValue) : this);
                  case INSTANT_SECONDS: return (newValue != seconds ? create(newValue, nanos) : this);
              }
              throw new UnsupportedTemporalTypeException("Unsupported field: " + field);
          }
          return field.adjustInto(this, newValue);
      }
  
      //-----------------------------------------------------------------------
      /**
       * Returns a copy of this {@code Instant} truncated to the specified unit.
       * <p>
       * Truncating the instant returns a copy of the original with fields
       * smaller than the specified unit set to zero.
       * The fields are calculated on the basis of using a UTC offset as seen
       * in {@code toString}.
       * For example, truncating with the {@link ChronoUnit#MINUTES MINUTES} unit will
       * round down to the nearest minute, setting the seconds and nanoseconds to zero.
       * <p>
       * The unit must have a {@linkplain TemporalUnit#getDuration() duration}
       * that divides into the length of a standard day without remainder.
       * This includes all supplied time units on {@link ChronoUnit} and
       * {@link ChronoUnit#DAYS DAYS}. Other units throw an exception.
       * <p>
       * This instance is immutable and unaffected by this method call.
       *
       * @param unit  the unit to truncate to, not null
       * @return an {@code Instant} based on this instant with the time truncated, not null
       * @throws DateTimeException if the unit is invalid for truncation
       * @throws UnsupportedTemporalTypeException if the unit is not supported
       */
      public Instant truncatedTo(TemporalUnit unit) {
          if (unit == ChronoUnit.NANOS) {
              return this;
          }
          Duration unitDur = unit.getDuration();
          if (unitDur.getSeconds() > LocalTime.SECONDS_PER_DAY) {
              throw new UnsupportedTemporalTypeException("Unit is too large to be used for truncation");
          }
          long dur = unitDur.toNanos();
          if ((LocalTime.NANOS_PER_DAY % dur) != 0) {
              throw new UnsupportedTemporalTypeException("Unit must divide into a standard day without remainder");
          }
          long nod = (seconds % LocalTime.SECONDS_PER_DAY) * LocalTime.NANOS_PER_SECOND + nanos;
          long result = (nod / dur) * dur;
          return plusNanos(result - nod);
      }
  
      //-----------------------------------------------------------------------
      /**
       * Returns a copy of this instant with the specified amount added.
       * <p>
       * This returns an {@code Instant}, based on this one, with the specified amount added.
       * The amount is typically {@link Duration} but may be any other type implementing
       * the {@link TemporalAmount} interface.
       * <p>
       * The calculation is delegated to the amount object by calling
       * {@link TemporalAmount#addTo(Temporal)}. The amount implementation is free
       * to implement the addition in any way it wishes, however it typically
       * calls back to {@link #plus(long, TemporalUnit)}. Consult the documentation
       * of the amount implementation to determine if it can be successfully added.
       * <p>
       * This instance is immutable and unaffected by this method call.
       *
       * @param amountToAdd  the amount to add, not null
       * @return an {@code Instant} based on this instant with the addition made, not null
       * @throws DateTimeException if the addition cannot be made
       * @throws ArithmeticException if numeric overflow occurs
       */
      @Override
      public Instant plus(TemporalAmount amountToAdd) {
          return (Instant) amountToAdd.addTo(this);
      }
  
      /**
       * Returns a copy of this instant with the specified amount added.
       * <p>
       * This returns an {@code Instant}, based on this one, with the amount
       * in terms of the unit added. If it is not possible to add the amount, because the
       * unit is not supported or for some other reason, an exception is thrown.
       * <p>
       * If the field is a {@link ChronoUnit} then the addition is implemented here.
       * The supported fields behave as follows:
       * <ul>
       * <li>{@code NANOS} -
       *  Returns a {@code Instant} with the specified number of nanoseconds added.
       *  This is equivalent to {@link #plusNanos(long)}.
       * <li>{@code MICROS} -
       *  Returns a {@code Instant} with the specified number of microseconds added.
       *  This is equivalent to {@link #plusNanos(long)} with the amount
       *  multiplied by 1,000.
       * <li>{@code MILLIS} -
       *  Returns a {@code Instant} with the specified number of milliseconds added.
       *  This is equivalent to {@link #plusNanos(long)} with the amount
       *  multiplied by 1,000,000.
       * <li>{@code SECONDS} -
       *  Returns a {@code Instant} with the specified number of seconds added.
       *  This is equivalent to {@link #plusSeconds(long)}.
       * <li>{@code MINUTES} -
       *  Returns a {@code Instant} with the specified number of minutes added.
       *  This is equivalent to {@link #plusSeconds(long)} with the amount
       *  multiplied by 60.
       * <li>{@code HOURS} -
       *  Returns a {@code Instant} with the specified number of hours added.
       *  This is equivalent to {@link #plusSeconds(long)} with the amount
       *  multiplied by 3,600.
       * <li>{@code HALF_DAYS} -
       *  Returns a {@code Instant} with the specified number of half-days added.
       *  This is equivalent to {@link #plusSeconds(long)} with the amount
       *  multiplied by 43,200 (12 hours).
       * <li>{@code DAYS} -
       *  Returns a {@code Instant} with the specified number of days added.
       *  This is equivalent to {@link #plusSeconds(long)} with the amount
       *  multiplied by 86,400 (24 hours).
       * </ul>
       * <p>
       * All other {@code ChronoUnit} instances will throw an {@code UnsupportedTemporalTypeException}.
       * <p>
       * If the field is not a {@code ChronoUnit}, then the result of this method
       * is obtained by invoking {@code TemporalUnit.addTo(Temporal, long)}
       * passing {@code this} as the argument. In this case, the unit determines
       * whether and how to perform the addition.
       * <p>
       * This instance is immutable and unaffected by this method call.
       *
       * @param amountToAdd  the amount of the unit to add to the result, may be negative
       * @param unit  the unit of the amount to add, not null
       * @return an {@code Instant} based on this instant with the specified amount added, not null
       * @throws DateTimeException if the addition cannot be made
       * @throws UnsupportedTemporalTypeException if the unit is not supported
       * @throws ArithmeticException if numeric overflow occurs
       */
      @Override
      public Instant plus(long amountToAdd, TemporalUnit unit) {
          if (unit instanceof ChronoUnit) {
              switch ((ChronoUnit) unit) {
                  case NANOS: return plusNanos(amountToAdd);
                  case MICROS: return plus(amountToAdd / 1000_000, (amountToAdd % 1000_000) * 1000);
                  case MILLIS: return plusMillis(amountToAdd);
                  case SECONDS: return plusSeconds(amountToAdd);
                  case MINUTES: return plusSeconds(Math.multiplyExact(amountToAdd, SECONDS_PER_MINUTE));
                  case HOURS: return plusSeconds(Math.multiplyExact(amountToAdd, SECONDS_PER_HOUR));
                  case HALF_DAYS: return plusSeconds(Math.multiplyExact(amountToAdd, SECONDS_PER_DAY / 2));
                  case DAYS: return plusSeconds(Math.multiplyExact(amountToAdd, SECONDS_PER_DAY));
              }
              throw new UnsupportedTemporalTypeException("Unsupported unit: " + unit);
          }
          return unit.addTo(this, amountToAdd);
      }
  
      //-----------------------------------------------------------------------
      /**
       * Returns a copy of this instant with the specified duration in seconds added.
       * <p>
       * This instance is immutable and unaffected by this method call.
       *
       * @param secondsToAdd  the seconds to add, positive or negative
       * @return an {@code Instant} based on this instant with the specified seconds added, not null
       * @throws DateTimeException if the result exceeds the maximum or minimum instant
       * @throws ArithmeticException if numeric overflow occurs
       */
      public Instant plusSeconds(long secondsToAdd) {
          return plus(secondsToAdd, 0);
      }
  
      /**
       * Returns a copy of this instant with the specified duration in milliseconds added.
       * <p>
       * This instance is immutable and unaffected by this method call.
       *
       * @param millisToAdd  the milliseconds to add, positive or negative
       * @return an {@code Instant} based on this instant with the specified milliseconds added, not null
       * @throws DateTimeException if the result exceeds the maximum or minimum instant
       * @throws ArithmeticException if numeric overflow occurs
       */
      public Instant plusMillis(long millisToAdd) {
          return plus(millisToAdd / 1000, (millisToAdd % 1000) * 1000_000);
      }
  
      /**
       * Returns a copy of this instant with the specified duration in nanoseconds added.
       * <p>
       * This instance is immutable and unaffected by this method call.
       *
       * @param nanosToAdd  the nanoseconds to add, positive or negative
       * @return an {@code Instant} based on this instant with the specified nanoseconds added, not null
       * @throws DateTimeException if the result exceeds the maximum or minimum instant
       * @throws ArithmeticException if numeric overflow occurs
       */
      public Instant plusNanos(long nanosToAdd) {
          return plus(0, nanosToAdd);
      }
  
      /**
       * Returns a copy of this instant with the specified duration added.
       * <p>
       * This instance is immutable and unaffected by this method call.
       *
       * @param secondsToAdd  the seconds to add, positive or negative
       * @param nanosToAdd  the nanos to add, positive or negative
       * @return an {@code Instant} based on this instant with the specified seconds added, not null
       * @throws DateTimeException if the result exceeds the maximum or minimum instant
       * @throws ArithmeticException if numeric overflow occurs
       */
      private Instant plus(long secondsToAdd, long nanosToAdd) {
          if ((secondsToAdd | nanosToAdd) == 0) {
              return this;
          }
          long epochSec = Math.addExact(seconds, secondsToAdd);
          epochSec = Math.addExact(epochSec, nanosToAdd / NANOS_PER_SECOND);
          nanosToAdd = nanosToAdd % NANOS_PER_SECOND;
          long nanoAdjustment = nanos + nanosToAdd;  // safe int+NANOS_PER_SECOND
          return ofEpochSecond(epochSec, nanoAdjustment);
      }
  
      //-----------------------------------------------------------------------
      /**
       * Returns a copy of this instant with the specified amount subtracted.
       * <p>
       * This returns an {@code Instant}, based on this one, with the specified amount subtracted.
       * The amount is typically {@link Duration} but may be any other type implementing
       * the {@link TemporalAmount} interface.
       * <p>
       * The calculation is delegated to the amount object by calling
       * {@link TemporalAmount#subtractFrom(Temporal)}. The amount implementation is free
       * to implement the subtraction in any way it wishes, however it typically
       * calls back to {@link #minus(long, TemporalUnit)}. Consult the documentation
       * of the amount implementation to determine if it can be successfully subtracted.
       * <p>
       * This instance is immutable and unaffected by this method call.
       *
       * @param amountToSubtract  the amount to subtract, not null
       * @return an {@code Instant} based on this instant with the subtraction made, not null
       * @throws DateTimeException if the subtraction cannot be made
       * @throws ArithmeticException if numeric overflow occurs
       */
      @Override
      public Instant minus(TemporalAmount amountToSubtract) {
          return (Instant) amountToSubtract.subtractFrom(this);
      }
  
      /**
       * Returns a copy of this instant with the specified amount subtracted.
       * <p>
       * This returns a {@code Instant}, based on this one, with the amount
       * in terms of the unit subtracted. If it is not possible to subtract the amount,
       * because the unit is not supported or for some other reason, an exception is thrown.
       * <p>
       * This method is equivalent to {@link #plus(long, TemporalUnit)} with the amount negated.
       * See that method for a full description of how addition, and thus subtraction, works.
       * <p>
       * This instance is immutable and unaffected by this method call.
       *
       * @param amountToSubtract  the amount of the unit to subtract from the result, may be negative
       * @param unit  the unit of the amount to subtract, not null
       * @return an {@code Instant} based on this instant with the specified amount subtracted, not null
       * @throws DateTimeException if the subtraction cannot be made
       * @throws UnsupportedTemporalTypeException if the unit is not supported
       * @throws ArithmeticException if numeric overflow occurs
       */
      @Override
      public Instant minus(long amountToSubtract, TemporalUnit unit) {
          return (amountToSubtract == Long.MIN_VALUE ? plus(Long.MAX_VALUE, unit).plus(1, unit) : plus(-amountToSubtract, unit));
      }
  
      //-----------------------------------------------------------------------
      /**
       * Returns a copy of this instant with the specified duration in seconds subtracted.
       * <p>
       * This instance is immutable and unaffected by this method call.
       *
       * @param secondsToSubtract  the seconds to subtract, positive or negative
       * @return an {@code Instant} based on this instant with the specified seconds subtracted, not null
       * @throws DateTimeException if the result exceeds the maximum or minimum instant
       * @throws ArithmeticException if numeric overflow occurs
       */
      public Instant minusSeconds(long secondsToSubtract) {
          if (secondsToSubtract == Long.MIN_VALUE) {
              return plusSeconds(Long.MAX_VALUE).plusSeconds(1);
          }
          return plusSeconds(-secondsToSubtract);
      }
  
      /**
       * Returns a copy of this instant with the specified duration in milliseconds subtracted.
       * <p>
       * This instance is immutable and unaffected by this method call.
       *
       * @param millisToSubtract  the milliseconds to subtract, positive or negative
       * @return an {@code Instant} based on this instant with the specified milliseconds subtracted, not null
       * @throws DateTimeException if the result exceeds the maximum or minimum instant
       * @throws ArithmeticException if numeric overflow occurs
       */
      public Instant minusMillis(long millisToSubtract) {
          if (millisToSubtract == Long.MIN_VALUE) {
              return plusMillis(Long.MAX_VALUE).plusMillis(1);
          }
          return plusMillis(-millisToSubtract);
      }
  
      /**
       * Returns a copy of this instant with the specified duration in nanoseconds subtracted.
       * <p>
       * This instance is immutable and unaffected by this method call.
       *
       * @param nanosToSubtract  the nanoseconds to subtract, positive or negative
       * @return an {@code Instant} based on this instant with the specified nanoseconds subtracted, not null
       * @throws DateTimeException if the result exceeds the maximum or minimum instant
       * @throws ArithmeticException if numeric overflow occurs
       */
      public Instant minusNanos(long nanosToSubtract) {
          if (nanosToSubtract == Long.MIN_VALUE) {
              return plusNanos(Long.MAX_VALUE).plusNanos(1);
          }
          return plusNanos(-nanosToSubtract);
      }
  
      //-------------------------------------------------------------------------
      /**
       * Queries this instant using the specified query.
       * <p>
       * This queries this instant using the specified query strategy object.
       * The {@code TemporalQuery} object defines the logic to be used to
       * obtain the result. Read the documentation of the query to understand
       * what the result of this method will be.
       * <p>
       * The result of this method is obtained by invoking the
       * {@link TemporalQuery#queryFrom(TemporalAccessor)} method on the
       * specified query passing {@code this} as the argument.
       *
       * @param <R> the type of the result
       * @param query  the query to invoke, not null
       * @return the query result, null may be returned (defined by the query)
       * @throws DateTimeException if unable to query (defined by the query)
       * @throws ArithmeticException if numeric overflow occurs (defined by the query)
       */
      @SuppressWarnings("unchecked")
      @Override
      public <R> R query(TemporalQuery<R> query) {
          if (query == TemporalQueries.precision()) {
              return (R) NANOS;
          }
          // inline TemporalAccessor.super.query(query) as an optimization
          if (query == TemporalQueries.chronology() || query == TemporalQueries.zoneId() ||
                  query == TemporalQueries.zone() || query == TemporalQueries.offset() ||
                  query == TemporalQueries.localDate() || query == TemporalQueries.localTime()) {
              return null;
          }
          return query.queryFrom(this);
      }
  
      /**
       * Adjusts the specified temporal object to have this instant.
       * <p>
       * This returns a temporal object of the same observable type as the input
       * with the instant changed to be the same as this.
       * <p>
       * The adjustment is equivalent to using {@link Temporal#with(TemporalField, long)}
       * twice, passing {@link ChronoField#INSTANT_SECONDS} and
       * {@link ChronoField#NANO_OF_SECOND} as the fields.
       * <p>
       * In most cases, it is clearer to reverse the calling pattern by using
       * {@link Temporal#with(TemporalAdjuster)}:
       * <pre>
       *   // these two lines are equivalent, but the second approach is recommended
       *   temporal = thisInstant.adjustInto(temporal);
       *   temporal = temporal.with(thisInstant);
       * </pre>
       * <p>
       * This instance is immutable and unaffected by this method call.
       *
       * @param temporal  the target object to be adjusted, not null
       * @return the adjusted object, not null
       * @throws DateTimeException if unable to make the adjustment
       * @throws ArithmeticException if numeric overflow occurs
       */
      @Override
      public Temporal adjustInto(Temporal temporal) {
          return temporal.with(INSTANT_SECONDS, seconds).with(NANO_OF_SECOND, nanos);
      }
  
      /**
       * Calculates the amount of time until another instant in terms of the specified unit.
       * <p>
       * This calculates the amount of time between two {@code Instant}
       * objects in terms of a single {@code TemporalUnit}.
       * The start and end points are {@code this} and the specified instant.
       * The result will be negative if the end is before the start.
       * The calculation returns a whole number, representing the number of
       * complete units between the two instants.
       * The {@code Temporal} passed to this method is converted to a
       * {@code Instant} using {@link #from(TemporalAccessor)}.
       * For example, the amount in days between two dates can be calculated
       * using {@code startInstant.until(endInstant, SECONDS)}.
       * <p>
       * There are two equivalent ways of using this method.
       * The first is to invoke this method.
       * The second is to use {@link TemporalUnit#between(Temporal, Temporal)}:
       * <pre>
       *   // these two lines are equivalent
       *   amount = start.until(end, SECONDS);
       *   amount = SECONDS.between(start, end);
       * </pre>
       * The choice should be made based on which makes the code more readable.
       * <p>
       * The calculation is implemented in this method for {@link ChronoUnit}.
       * The units {@code NANOS}, {@code MICROS}, {@code MILLIS}, {@code SECONDS},
       * {@code MINUTES}, {@code HOURS}, {@code HALF_DAYS} and {@code DAYS}
       * are supported. Other {@code ChronoUnit} values will throw an exception.
       * <p>
       * If the unit is not a {@code ChronoUnit}, then the result of this method
       * is obtained by invoking {@code TemporalUnit.between(Temporal, Temporal)}
       * passing {@code this} as the first argument and the converted input temporal
       * as the second argument.
       * <p>
       * This instance is immutable and unaffected by this method call.
       *
       * @param endExclusive  the end date, exclusive, which is converted to an {@code Instant}, not null
       * @param unit  the unit to measure the amount in, not null
       * @return the amount of time between this instant and the end instant
       * @throws DateTimeException if the amount cannot be calculated, or the end
       *  temporal cannot be converted to an {@code Instant}
       * @throws UnsupportedTemporalTypeException if the unit is not supported
       * @throws ArithmeticException if numeric overflow occurs
       */
      @Override
      public long until(Temporal endExclusive, TemporalUnit unit) {
          Instant end = Instant.from(endExclusive);
          if (unit instanceof ChronoUnit) {
              ChronoUnit f = (ChronoUnit) unit;
              switch (f) {
                  case NANOS: return nanosUntil(end);
                  case MICROS: return nanosUntil(end) / 1000;
                  case MILLIS: return Math.subtractExact(end.toEpochMilli(), toEpochMilli());
                  case SECONDS: return secondsUntil(end);
                  case MINUTES: return secondsUntil(end) / SECONDS_PER_MINUTE;
                  case HOURS: return secondsUntil(end) / SECONDS_PER_HOUR;
                  case HALF_DAYS: return secondsUntil(end) / (12 * SECONDS_PER_HOUR);
                  case DAYS: return secondsUntil(end) / (SECONDS_PER_DAY);
              }
              throw new UnsupportedTemporalTypeException("Unsupported unit: " + unit);
          }
          return unit.between(this, end);
      }
  
      private long nanosUntil(Instant end) {
          long secsDiff = Math.subtractExact(end.seconds, seconds);
          long totalNanos = Math.multiplyExact(secsDiff, NANOS_PER_SECOND);
          return Math.addExact(totalNanos, end.nanos - nanos);
      }
  
      private long secondsUntil(Instant end) {
          long secsDiff = Math.subtractExact(end.seconds, seconds);
          long nanosDiff = end.nanos - nanos;
          if (secsDiff > 0 && nanosDiff < 0) {
              secsDiff--;
          } else if (secsDiff < 0 && nanosDiff > 0) {
              secsDiff++;
          }
          return secsDiff;
      }
  
      //-----------------------------------------------------------------------
      /**
       * Combines this instant with an offset to create an {@code OffsetDateTime}.
       * <p>
       * This returns an {@code OffsetDateTime} formed from this instant at the
       * specified offset from UTC/Greenwich. An exception will be thrown if the
       * instant is too large to fit into an offset date-time.
       * <p>
       * This method is equivalent to
       * {@link OffsetDateTime#ofInstant(Instant, ZoneId) OffsetDateTime.ofInstant(this, offset)}.
       *
       * @param offset  the offset to combine with, not null
       * @return the offset date-time formed from this instant and the specified offset, not null
       * @throws DateTimeException if the result exceeds the supported range
       */
      public OffsetDateTime atOffset(ZoneOffset offset) {
          return OffsetDateTime.ofInstant(this, offset);
      }
  
      /**
       * Combines this instant with a time-zone to create a {@code ZonedDateTime}.
       * <p>
       * This returns an {@code ZonedDateTime} formed from this instant at the
       * specified time-zone. An exception will be thrown if the instant is too
       * large to fit into a zoned date-time.
       * <p>
       * This method is equivalent to
       * {@link ZonedDateTime#ofInstant(Instant, ZoneId) ZonedDateTime.ofInstant(this, zone)}.
       *
       * @param zone  the zone to combine with, not null
       * @return the zoned date-time formed from this instant and the specified zone, not null
       * @throws DateTimeException if the result exceeds the supported range
       */
      public ZonedDateTime atZone(ZoneId zone) {
          return ZonedDateTime.ofInstant(this, zone);
      }
  
      //-----------------------------------------------------------------------
      /**
       * Converts this instant to the number of milliseconds from the epoch
       * of 1970-01-01T00:00:00Z.
       * <p>
       * If this instant represents a point on the time-line too far in the future
       * or past to fit in a {@code long} milliseconds, then an exception is thrown.
       * <p>
       * If this instant has greater than millisecond precision, then the conversion
       * will drop any excess precision information as though the amount in nanoseconds
       * was subject to integer division by one million.
       *
       * @return the number of milliseconds since the epoch of 1970-01-01T00:00:00Z
       * @throws ArithmeticException if numeric overflow occurs
       */
      public long toEpochMilli() {
          if (seconds < 0 && nanos > 0) {
              long millis = Math.multiplyExact(seconds+1, 1000);
              long adjustment = nanos / 1000_000 - 1000;
              return Math.addExact(millis, adjustment);
          } else {
              long millis = Math.multiplyExact(seconds, 1000);
              return Math.addExact(millis, nanos / 1000_000);
          }
      }
  
      //-----------------------------------------------------------------------
      /**
       * Compares this instant to the specified instant.
       * <p>
       * The comparison is based on the time-line position of the instants.
       * It is "consistent with equals", as defined by {@link Comparable}.
       *
       * @param otherInstant  the other instant to compare to, not null
       * @return the comparator value, negative if less, positive if greater
       * @throws NullPointerException if otherInstant is null
       */
      @Override
      public int compareTo(Instant otherInstant) {
          int cmp = Long.compare(seconds, otherInstant.seconds);
          if (cmp != 0) {
              return cmp;
          }
          return nanos - otherInstant.nanos;
      }
  
      /**
       * Checks if this instant is after the specified instant.
       * <p>
       * The comparison is based on the time-line position of the instants.
       *
       * @param otherInstant  the other instant to compare to, not null
       * @return true if this instant is after the specified instant
       * @throws NullPointerException if otherInstant is null
       */
      public boolean isAfter(Instant otherInstant) {
          return compareTo(otherInstant) > 0;
      }
  
      /**
       * Checks if this instant is before the specified instant.
       * <p>
       * The comparison is based on the time-line position of the instants.
       *
       * @param otherInstant  the other instant to compare to, not null
       * @return true if this instant is before the specified instant
       * @throws NullPointerException if otherInstant is null
       */
      public boolean isBefore(Instant otherInstant) {
          return compareTo(otherInstant) < 0;
      }
  
      //-----------------------------------------------------------------------
      /**
       * Checks if this instant is equal to the specified instant.
       * <p>
       * The comparison is based on the time-line position of the instants.
       *
       * @param otherInstant  the other instant, null returns false
       * @return true if the other instant is equal to this one
       */
      @Override
      public boolean equals(Object otherInstant) {
          if (this == otherInstant) {
              return true;
          }
          if (otherInstant instanceof Instant) {
              Instant other = (Instant) otherInstant;
              return this.seconds == other.seconds &&
                     this.nanos == other.nanos;
          }
          return false;
      }
  
      /**
       * Returns a hash code for this instant.
       *
       * @return a suitable hash code
       */
      @Override
      public int hashCode() {
          return ((int) (seconds ^ (seconds >>> 32))) + 51 * nanos;
      }
  
      //-----------------------------------------------------------------------
      /**
       * A string representation of this instant using ISO-8601 representation.
       * <p>
       * The format used is the same as {@link DateTimeFormatter#ISO_INSTANT}.
       *
       * @return an ISO-8601 representation of this instant, not null
       */
      @Override
      public String toString() {
          return DateTimeFormatter.ISO_INSTANT.format(this);
      }
  
      // -----------------------------------------------------------------------
      /**
       * Writes the object using a
       * <a href="../../serialized-form.html#java.time.Ser">dedicated serialized form</a>.
       * @serialData
       * <pre>
       *  out.writeByte(2);  // identifies an Instant
       *  out.writeLong(seconds);
       *  out.writeInt(nanos);
       * </pre>
       *
       * @return the instance of {@code Ser}, not null
       */
      private Object writeReplace() {
          return new Ser(Ser.INSTANT_TYPE, this);
      }
  
      /**
       * Defend against malicious streams.
       *
       * @param s the stream to read
       * @throws InvalidObjectException always
       */
      private void readObject(ObjectInputStream s) throws InvalidObjectException {
          throw new InvalidObjectException("Deserialization via serialization delegate");
      }
  
      void writeExternal(DataOutput out) throws IOException {
          out.writeLong(seconds);
          out.writeInt(nanos);
      }
  
      static Instant readExternal(DataInput in) throws IOException {
          long seconds = in.readLong();
          int nanos = in.readInt();
          return Instant.ofEpochSecond(seconds, nanos);
      }
  
  }
  