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/*

 * 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) 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.

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/**

 * <p>

 * The main API for dates, times, instants, and durations.

 * </p>

 * <p>

 * The classes defined here represent the principal date-time concepts,

 * including instants, durations, dates, times, time-zones and periods.

 * They are based on the ISO calendar system, which is the <i>de facto</i> world

 * calendar following the proleptic Gregorian rules.

 * All the classes are immutable and thread-safe.

 * </p>

 * <p>

 * Each date time instance is composed of fields that are conveniently

 * made available by the APIs.  For lower level access to the fields refer

 * to the {@code java.time.temporal} package.

 * Each class includes support for printing and parsing all manner of dates and times.

 * Refer to the {@code java.time.format} package for customization options.

 * </p>

 * <p>

 * The {@code java.time.chrono} package contains the calendar neutral API

 * {@link java.time.chrono.ChronoLocalDate ChronoLocalDate},

 * {@link java.time.chrono.ChronoLocalDateTime ChronoLocalDateTime},

 * {@link java.time.chrono.ChronoZonedDateTime ChronoZonedDateTime} and

 * {@link java.time.chrono.Era Era}.

 * This is intended for use by applications that need to use localized calendars.

 * It is recommended that applications use the ISO-8601 date and time classes from

 * this package across system boundaries, such as to the database or across the network.

 * The calendar neutral API should be reserved for interactions with users.

 * </p>

 *

 * <h3>Dates and Times</h3>

 * <p>

 * {@link java.time.Instant} is essentially a numeric timestamp.

 * The current Instant can be retrieved from a {@link java.time.Clock}.

 * This is useful for logging and persistence of a point in time

 * and has in the past been associated with storing the result

 * from {@link java.lang.System#currentTimeMillis()}.

 * </p>

 * <p>

 * {@link java.time.LocalDate} stores a date without a time.

 * This stores a date like '2010-12-03' and could be used to store a birthday.

 * </p>

 * <p>

 * {@link java.time.LocalTime} stores a time without a date.

 * This stores a time like '11:30' and could be used to store an opening or closing time.

 * </p>

 * <p>

 * {@link java.time.LocalDateTime} stores a date and time.

 * This stores a date-time like '2010-12-03T11:30'.

 * </p>

 * <p>

 * {@link java.time.ZonedDateTime} stores a date and time with a time-zone.

 * This is useful if you want to perform accurate calculations of

 * dates and times taking into account the {@link java.time.ZoneId}, such as 'Europe/Paris'.

 * Where possible, it is recommended to use a simpler class without a time-zone.

 * The widespread use of time-zones tends to add considerable complexity to an application.

 * </p>

 *

 * <h3>Duration and Period</h3>

 * <p>

 * Beyond dates and times, the API also allows the storage of period and durations of time.

 * A {@link java.time.Duration} is a simple measure of time along the time-line in nanoseconds.

 * A {@link java.time.Period} expresses an amount of time in units meaningful to humans, such as years or hours.

 * </p>

 *

 * <h3>Additional value types</h3>

 * <p>

 * {@link java.time.Month} stores a month on its own.

 * This stores a single month-of-year in isolation, such as 'DECEMBER'.

 * </p>

 * <p>

 * {@link java.time.DayOfWeek} stores a day-of-week on its own.

 * This stores a single day-of-week in isolation, such as 'TUESDAY'.

 * </p>

 * <p>

 * {@link java.time.Year} stores a year on its own.

 * This stores a single year in isolation, such as '2010'.

 * </p>

 * <p>

 * {@link java.time.YearMonth} stores a year and month without a day or time.

 * This stores a year and month, such as '2010-12' and could be used for a credit card expiry.

 * </p>

 * <p>

 * {@link java.time.MonthDay} stores a month and day without a year or time.

 * This stores a month and day-of-month, such as '--12-03' and

 * could be used to store an annual event like a birthday without storing the year.

 * </p>

 * <p>

 * {@link java.time.OffsetTime} stores a time and offset from UTC without a date.

 * This stores a date like '11:30+01:00'.

 * The {@link java.time.ZoneOffset ZoneOffset} is of the form '+01:00'.

 * </p>

 * <p>

 * {@link java.time.OffsetDateTime} stores a date and time and offset from UTC.

 * This stores a date-time like '2010-12-03T11:30+01:00'.

 * This is sometimes found in XML messages and other forms of persistence,

 * but contains less information than a full time-zone.

 * </p>

 *

 * <h3>Package specification</h3>

 * <p>

 * Unless otherwise noted, passing a null argument to a constructor or method in any class or interface

 * in this package will cause a {@link java.lang.NullPointerException NullPointerException} to be thrown.

 * The Javadoc "@param" definition is used to summarise the null-behavior.

 * The "@throws {@link java.lang.NullPointerException}" is not explicitly documented in each method.

 * </p>

 * <p>

 * All calculations should check for numeric overflow and throw either an {@link java.lang.ArithmeticException}

 * or a {@link java.time.DateTimeException}.

 * </p>

 *

 * <h3>Design notes (non normative)</h3>

 * <p>

 * The API has been designed to reject null early and to be clear about this behavior.

 * A key exception is any method that takes an object and returns a boolean, for the purpose

 * of checking or validating, will generally return false for null.

 * </p>

 * <p>

 * The API is designed to be type-safe where reasonable in the main high-level API.

 * Thus, there are separate classes for the distinct concepts of date, time and date-time,

 * plus variants for offset and time-zone.

 * This can seem like a lot of classes, but most applications can begin with just five date/time types.

 * <ul>

 * <li>{@link java.time.Instant} - a timestamp</li>

 * <li>{@link java.time.LocalDate} - a date without a time, or any reference to an offset or time-zone</li>

 * <li>{@link java.time.LocalTime} - a time without a date, or any reference to an offset or time-zone</li>

 * <li>{@link java.time.LocalDateTime} - combines date and time, but still without any offset or time-zone</li>

 * <li>{@link java.time.ZonedDateTime} - a "full" date-time with time-zone and resolved offset from UTC/Greenwich</li>

 * </ul>

 * <p>

 * {@code Instant} is the closest equivalent class to {@code java.util.Date}.

 * {@code ZonedDateTime} is the closest equivalent class to {@code java.util.GregorianCalendar}.

 * </p>

 * <p>

 * Where possible, applications should use {@code LocalDate}, {@code LocalTime} and {@code LocalDateTime}

 * to better model the domain. For example, a birthday should be stored in a code {@code LocalDate}.

 * Bear in mind that any use of a {@linkplain java.time.ZoneId time-zone}, such as 'Europe/Paris', adds

 * considerable complexity to a calculation.

 * Many applications can be written only using {@code LocalDate}, {@code LocalTime} and {@code Instant},

 * with the time-zone added at the user interface (UI) layer.

 * </p>

 * <p>

 * The offset-based date-time types {@code OffsetTime} and {@code OffsetDateTime},

 * are intended primarily for use with network protocols and database access.

 * For example, most databases cannot automatically store a time-zone like 'Europe/Paris', but

 * they can store an offset like '+02:00'.

 * </p>

 * <p>

 * Classes are also provided for the most important sub-parts of a date, including {@code Month},

 * {@code DayOfWeek}, {@code Year}, {@code YearMonth} and {@code MonthDay}.

 * These can be used to model more complex date-time concepts.

 * For example, {@code YearMonth} is useful for representing a credit card expiry.

 * </p>

 * <p>

 * Note that while there are a large number of classes representing different aspects of dates,

 * there are relatively few dealing with different aspects of time.

 * Following type-safety to its logical conclusion would have resulted in classes for

 * hour-minute, hour-minute-second and hour-minute-second-nanosecond.

 * While logically pure, this was not a practical option as it would have almost tripled the

 * number of classes due to the combinations of date and time.

 * Thus, {@code LocalTime} is used for all precisions of time, with zeroes used to imply lower precision.

 * </p>

 * <p>

 * Following full type-safety to its ultimate conclusion might also argue for a separate class

 * for each field in date-time, such as a class for HourOfDay and another for DayOfMonth.

 * This approach was tried, but was excessively complicated in the Java language, lacking usability.

 * A similar problem occurs with periods.

 * There is a case for a separate class for each period unit, such as a type for Years and a type for Minutes.

 * However, this yields a lot of classes and a problem of type conversion.

 * Thus, the set of date-time types provided is a compromise between purity and practicality.

 * </p>

 * <p>

 * The API has a relatively large surface area in terms of number of methods.

 * This is made manageable through the use of consistent method prefixes.

 * <ul>

 * <li>{@code of} - static factory method</li>

 * <li>{@code parse} - static factory method focussed on parsing</li>

 * <li>{@code get} - gets the value of something</li>

 * <li>{@code is} - checks if something is true</li>

 * <li>{@code with} - the immutable equivalent of a setter</li>

 * <li>{@code plus} - adds an amount to an object</li>

 * <li>{@code minus} - subtracts an amount from an object</li>

 * <li>{@code to} - converts this object to another type</li>

 * <li>{@code at} - combines this object with another, such as {@code date.atTime(time)}</li>

 * </ul>

 * <p>

 * Multiple calendar systems is an awkward addition to the design challenges.

 * The first principal is that most users want the standard ISO calendar system.

 * As such, the main classes are ISO-only. The second principal is that most of those that want a

 * non-ISO calendar system want it for user interaction, thus it is a UI localization issue.

 * As such, date and time objects should be held as ISO objects in the data model and persistent

 * storage, only being converted to and from a local calendar for display.

 * The calendar system would be stored separately in the user preferences.

 * </p>

 * <p>

 * There are, however, some limited use cases where users believe they need to store and use

 * dates in arbitrary calendar systems throughout the application.

 * This is supported by {@link java.time.chrono.ChronoLocalDate}, however it is vital to read

 * all the associated warnings in the Javadoc of that interface before using it.

 * In summary, applications that require general interoperation between multiple calendar systems

 * typically need to be written in a very different way to those only using the ISO calendar,

 * thus most applications should just use ISO and avoid {@code ChronoLocalDate}.

 * </p>

 * <p>

 * The API is also designed for user extensibility, as there are many ways of calculating time.

 * The {@linkplain java.time.temporal.TemporalField field} and {@linkplain java.time.temporal.TemporalUnit unit}

 * API, accessed via {@link java.time.temporal.TemporalAccessor TemporalAccessor} and

 * {@link java.time.temporal.Temporal Temporal} provide considerable flexibility to applications.

 * In addition, the {@link java.time.temporal.TemporalQuery TemporalQuery} and

 * {@link java.time.temporal.TemporalAdjuster TemporalAdjuster} interfaces provide day-to-day

 * power, allowing code to read close to business requirements:

 * </p>

 * <pre>

 *   LocalDate customerBirthday = customer.loadBirthdayFromDatabase();

 *   LocalDate today = LocalDate.now();

 *   if (customerBirthday.equals(today)) {

 *     LocalDate specialOfferExpiryDate = today.plusWeeks(2).with(next(FRIDAY));

 *     customer.sendBirthdaySpecialOffer(specialOfferExpiryDate);

 *   }

 *

 * </pre>

 *

 * @since JDK1.8

 */

package java.time;