* The main API for dates, times, instants, and durations. *
** The classes defined here represent the principle date-time concepts, including instants, durations, dates, times, * time-zones and periods. They are based on the ISO calendar system, which is the de facto world calendar * following the proleptic Gregorian rules. All the classes are immutable and thread-safe. *
** 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. *
** 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. *
* ** {@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()}. *
** {@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. *
** {@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. *
** {@link java.time.LocalDateTime} stores a date and time. This stores a date-time like '2010-12-03T11:30'. *
** {@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. *
* ** Beyond dates and times, the API also allows the storage of periods 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 days. *
* ** {@link java.time.Month} stores a month on its own. This stores a single month-of-year in isolation, such as * 'DECEMBER'. *
** {@link java.time.DayOfWeek} stores a day-of-week on its own. This stores a single day-of-week in isolation, such as * 'TUESDAY'. *
** {@link java.time.Year} stores a year on its own. This stores a single year in isolation, such as '2010'. *
** {@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. *
** {@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. *
** {@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'. *
** {@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. *
* ** The Javadoc "@param" definition is used to summarise the null-behavior. *
* ** 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. *
* {@code Instant} is the closest equivalent class to {@code java.util.Date}. {@code ZonedDateTime} is the closest * equivalent class to {@code java.util.GregorianCalendar}. *
** 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. *
** 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'. *
** 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. *
** 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. *
** 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. *
** 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. *
* Multiple calendar systems is an awkward addition to the design challenges. The first principle is that most users * want the standard ISO calendar system. As such, the main classes are ISO-only. The second principle 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. *
** 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}. *
** 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: *
* *
* LocalDate customerBirthday = customer.loadBirthdayFromDatabase();
* LocalDate today = LocalDate.now();
* if (customerBirthday.equals(today)) {
* LocalDate specialOfferExpiryDate = today.plusWeeks(2).with(next(FRIDAY));
* customer.sendBirthdaySpecialOffer(specialOfferExpiryDate);
* }
*
*
*/
@ej.annotation.NonNullByDefault
package java.time;