18-December-2012 05:30

Package javax.time.temporal

Access to date and time using fields and units, additional value type classes and base support for calendar systems other than the default ISO.

See: Description

Package javax.time.temporal Description

Access to date and time using fields and units, additional value type classes and base support for calendar systems other than the default ISO.

This package expands on the base package to provide additional functionality for more powerful use cases. Support is included for:

Fields and Units

Dates and times are expressed in terms of fields and units. A unit is used to measure an amount of time, such as years, days or minutes. All units implement TemporalUnit. The set of well known units is defined in ChronoUnit, for example, ChronoUnit.DAYS. The unit interface is designed to allow applications to add their own units.

A field is used to express part of a larger date-time, such as year, month-of-year or second-of-minute. All fields implement TemporalField. The set of well known fields are defined in ChronoField, for example, ChronoField.HOUR_OF_DAY. An additional fields are defined by JulianDayField. The field interface is designed to allow applications to add their own fields.

This package provides tools that allow the units and fields of date and time to be accessed in a general way most suited for frameworks. Temporal provides the abstraction for date time types that support fields. Its methods support getting the value of a field, creating a new date time with the value of a field modified, and extracting another date time type, typically used to extract the offset or time-zone.

One use of fields in application code is to retrieve fields for which there is no convenience method. For example, getting the day-of-month is common enough that there is a method on LocalDate called getDayOfMonth(). However for more unusual fields it is necessary to use the field. For example, date.get(ChronoField.ALIGNED_WEEK_OF_MONTH). The fields also provide access to the range of valid values.

Adjustment

A key part of the date-time problem space is adjusting a date to a new, related value, such as the "last day of the month", or "next Wednesday". These are modeled as functions that adjust a base date-time. The functions implement Temporal.WithAdjuster and operate on Temporal. A set of common functions are provided in Adjusters. For example, to find the first occurrence of a day-of-week after a given date, use Adjusters.next(DayOfWeek), such as date.with(next(MONDAY)).

Weeks

Different locales have different definitions of the week. For example, in Europe the week typically starts on a Monday, while in the US it starts on a Sunday. The WeekDefinition class models this distinction.

The ISO calendar system defines an additional week-based division of years. This defines a year based on whole Monday to Monday weeks. This is modeled in ISOFields.

Alternate calendar systems

The main API is based around the calendar system defined in ISO-8601. However, there are other calendar systems, and this package provides basic support for them. The alternate calendars are provided in the javax.time.calendar package.

A calendar system is defined by the Chrono interface, while a date in a calendar system is defined by the ChronoLocalDate interface.

It is intended that applications use the main API whenever possible, including code to read and write from a persistent data store, such as a database, and to send dates and times across a network. The "chrono" classes are then used at the user interface level to deal with localized input/output.

Using non-ISO calendar systems in an application introduces significant extra complexity. Ensure that the warnings and recommendations in ChronoLocalDate have been read before working with the "chrono" interfaces.

This example creates and uses a date in a non-ISO calendar system. 

        // Print the Minguo date
        ChronoLocalDate<MinguoChrono> now1 = MinguoChrono.INSTANCE.now();
        int day = now1.get(ChronoField.DAY_OF_MONTH);
        int dow = now1.get(ChronoField.DAY_OF_WEEK);
        int month = now1.get(ChronoField.MONTH_OF_YEAR);
        int year = now1.get(ChronoField.YEAR);
        System.out.printf("  Today is %s %s %d-%s-%d%n",
            now1.getChrono().getId(), dow, day, month, year);

        // Enumerate the list of available calendars and print today for each
        Set<String> names = Chrono.getAvailableIds();
        for (String name : names) {
            Chrono<?> chrono = Chrono.of(name);
            ChronoLocalDate<?> date = chrono.now();
            System.out.printf("   %20s: %s%n", chrono.getId(), date.toString());
        }

        // Print today's date and the last day of the year for the Minguo Calendar.
        ChronoLocalDate<MinguoChrono> first = now1
                .with(ChronoField.DAY_OF_MONTH, 1)
                .with(ChronoField.MONTH_OF_YEAR, 1);
        ChronoLocalDate<MinguoChrono> last = first
                .plus(1, ChronoUnit.YEARS)
                .minus(1, ChronoUnit.DAYS);
        System.out.printf("  %s: 1st of year: %s; end of year: %s%n", last.getChrono().getId(), first, last);
18-December-2012 05:30