Package org.joda.time

Provides support for dates, times, time zones, durations, intervals, and partials.

See: Description

Interface Summary

Interface	Description
DateTimeUtils.MillisProvider	A millisecond provider, allowing control of the system clock.
ReadableDateTime	Defines an instant in time that can be queried using datetime fields.
ReadableDuration	Defines an exact duration of time in milliseconds.
ReadableInstant	Defines an instant in the datetime continuum.
ReadableInterval	Readable interface for an interval of time between two instants.
ReadablePartial	Defines a partial time that does not support every datetime field, and is thus a local time.
ReadablePeriod	Defines a time period specified in terms of individual duration fields such as years and days.
ReadWritableDateTime	Defines an instant in time that can be queried and modified using datetime fields.
ReadWritableInstant	Defines an instant in the datetime continuum that can be queried and modified.
ReadWritableInterval	Writable interface for an interval.
ReadWritablePeriod	Defines a duration of time that can be queried and modified using datetime fields.

Class Summary

Class	Description
Chronology	Chronology provides access to the individual date time fields for a chronological calendar system.
DateMidnight	Deprecated The time of midnight does not exist in some time zones where the daylight saving time forward shift skips the midnight hour.
DateMidnight.Property	DateMidnight.Property binds a DateMidnight to a DateTimeField allowing powerful datetime functionality to be easily accessed.
DateTime	DateTime is the standard implementation of an unmodifiable datetime class.
DateTime.Property	DateTime.Property binds a DateTime to a DateTimeField allowing powerful datetime functionality to be easily accessed.
DateTimeComparator	DateTimeComparator provides comparators to compare one date with another.
DateTimeConstants	DateTimeConstants is a non-instantiable class of constants used in the date time system.
DateTimeField	Defines the calculation engine for date and time fields.
DateTimeFieldType	Identifies a field, such as year or minuteOfHour, in a chronology-neutral way.
DateTimeUtils	DateTimeUtils provide public utility methods for the date-time library.
DateTimeZone	DateTimeZone represents a time zone.
Days	An immutable time period representing a number of days.
Duration	An immutable duration specifying a length of time in milliseconds.
DurationField	Defines the calculation engine for duration fields.
DurationFieldType	Identifies a duration field, such as years or minutes, in a chronology-neutral way.
Hours	An immutable time period representing a number of hours.
Instant	Instant is the standard implementation of a fully immutable instant in time.
Interval	Interval is the standard implementation of an immutable time interval.
JodaTimePermission	JodaTimePermission is used for securing global method calls in the Joda-Time library.
LocalDate	LocalDate is an immutable datetime class representing a date without a time zone.
LocalDate.Property	LocalDate.Property binds a LocalDate to a DateTimeField allowing powerful datetime functionality to be easily accessed.
LocalDateTime	LocalDateTime is an unmodifiable datetime class representing a datetime without a time zone.
LocalDateTime.Property	LocalDateTime.Property binds a LocalDateTime to a DateTimeField allowing powerful datetime functionality to be easily accessed.
LocalTime	LocalTime is an immutable time class representing a time without a time zone.
LocalTime.Property	LocalTime.Property binds a LocalTime to a DateTimeField allowing powerful datetime functionality to be easily accessed.
Minutes	An immutable time period representing a number of minutes.
MonthDay	MonthDay is an immutable partial supporting the monthOfYear and dayOfMonth fields.
MonthDay.Property	The property class for MonthDay.
Months	An immutable time period representing a number of months.
MutableDateTime	MutableDateTime is the standard implementation of a modifiable datetime class.
MutableDateTime.Property	MutableDateTime.Property binds a MutableDateTime to a DateTimeField allowing powerful datetime functionality to be easily accessed.
MutableInterval	MutableInterval is the standard implementation of a mutable time interval.
MutablePeriod	Standard mutable time period implementation.
Partial	Partial is an immutable partial datetime supporting any set of datetime fields.
Partial.Property	The property class for Partial.
Period	An immutable time period specifying a set of duration field values.
PeriodType	Controls a period implementation by specifying which duration fields are to be used.
Seconds	An immutable time period representing a number of seconds.
TimeOfDay	Deprecated Use LocalTime which has a much better internal implementation and has been available since 1.3
TimeOfDay.Property	Deprecated Use LocalTime which has a much better internal implementation
Weeks	An immutable time period representing a number of weeks.
YearMonth	YearMonth is an immutable partial supporting the year and monthOfYear fields.
YearMonth.Property	The property class for YearMonth.
YearMonthDay	Deprecated Use LocalDate which has a much better internal implementation and has been available since 1.3
YearMonthDay.Property	Deprecated Use LocalDate which has a much better internal implementation
Years	An immutable time period representing a number of years.

Exception Summary

Exception	Description
IllegalFieldValueException	Exception thrown when attempting to set a field outside its supported range.
IllegalInstantException	Exception thrown when attempting to create an instant or date-time that cannot exist.

Package org.joda.time Description

Provides support for dates, times, time zones, durations, intervals, and partials. This package aims to fully replace the Java Date, Calendar, and TimeZone classes. This implementation covers both the Gregorian/Julian calendar system and the ISO8601 standard. Additional calendar systems and extensions can be created as well.

The ISO8601 standard is the international standard for dates, times, durations, and intervals. It defines text representations, the first day of the week as Monday, and the first week in a year as having a Thursday in it. This standard is being increasingly used in computer interchange and is the agreed format for XML. For most uses, the ISO standard is the same as Gregorian, and is thus the preferred format.

Interfaces

The main API concepts are defined by interfaces:

• ReadableInstant - an instant in time
• ReadableDateTime - an instant in time with field accessors such as dayOfWeek
• ReadablePartial - a definition for local times that are not defined to the millisecond, such as the time of day
• ReadableDuration - a duration defined in milliseconds
• ReadablePeriod - a time period defined in fields such as hours and minutes
• ReadableInterval - a period of time between two instants

• ReadWritableInstant - an instant that can be modified
• ReadWritableDateTime - a datetime that can be modified
• ReadWritablePeriod - a time period that can be modified
• ReadWritableInterval - an interval that can be modified

These define the public interface to dates, times, periods, intervals and durations. As with java.util.Date and Calendar, the design is millisecond based with an epoch of 1970-01-01. This should enable easy conversions.

Implementations

The basic implementation of the ReadableInstant interface is Instant. This is a simple immutable class that stores the millisecond value and integrates with Java Date and Calendar. The class follows the definition of the millisecond instant fully, thus it references the ISO8601 calendar system and UTC time zone. If you are dealing with an instant in time but do not know, or do not want to specify, which calendar system it refers to, then you should use this class.

The main implementation class for datetimes is the DateTime class. This implements the ReadableDateTime interface, providing convenient methods to access the fields of the datetime. Conversion methods allow integration with the Java Date and Calendar classes.

Like Instant, DateTime is immutable, and it can be used safely in a multi-threaded environment. In order to be fully immutable, key classes are declared as final. Abstract superclasses are provided should you need to define your own implementations.

The concrete implementations of the ReadWritable... interfaces are named the same as their immutable counterparts, but with a "Mutable" prefix. For example, MutableDateTime implements ReadWritableDateTime, making datetime editing easy. Note that it is possible to use the immutable DateTime for modifying datetimes, however each modification method returns a new instance of DateTime.

Interface usage

The interfaces in Joda-Time are not designed to operate in the same way as those in the Java Collections Framework (List/Map/Set etc). The Joda-Time interfaces represent a core subset of the functionality available via the actual classes. Thus, much of the work of an application will probably use methods on the class, not on the interface. Your application must determine whether it should define dates in terms of the interfaces, or in terms of the classes.

The interfaces provide simple methods to access an instance of the immutable class, which is implemented either via typecast or object creation. Thus, if you hold a reference to a ReadableInstant, and you call the method toDateTime(), the same instance will be returned (typecast) if it already was a DateTime.

Chronologies and Fields

In order to enable the package to be easily extended, each field of the datetime, such as the month, is calculated by an implementation of DateTimeField. Likewise, duration fields are calculated by specialized DurationField instances. If desired, users can write their own implementations to retrieve an unusual field from the millisecond value.

The datetime and duration fields that together represent a calendar system are grouped into a Chronology. The chronology represents all the information to convert from a millisecond value to human understandable fields in a specific calendar system. Chronologies are provided for ISO, Gregorian/Julian (GJ), Buddhist, Coptic and Ethiopic. More implementations are sought from the community.

The chronology and field classes are singletons. This design results in a low overhead on the date and time classes. The Java Calendar class performs poorly because it has many internal fields that are constantly kept in sync. This design only calculates fields when required, resulting in lightweight and simple date time classes.

When reviewing the library for the first time, it is easy to mistake the number of classes with complexity. The library is in fact clearly divided between user packages and implementation packages in the javadoc. Most users will should not need to be concerned with the back-end implementation.

Partials

Partials are like instants, except they do not completely specify a point in time. The main interface is ReadablePartial.

The main implementations are:

• LocalTime - A class storing a local time without a date
• LocalDate - A class storing a local date without a time
• LocalDateTime - A class storing a local datetime
• Partial - A class storing any combination of datetime fields, such as dayOfMonth and dayOfWeek

For consistency, the API of each partial class is similar to that of an instant class.

All partial implementations represent a local time, in other words without a time zone. Thus, to convert a partial to an instant (which does contain a time zone) requires adding a zone.

Formatting

Formatting is provided by the format subpackage. Comprehensive support is provided for outputting dates and times in multiple formats. A pattern similar to Java SimpleDateFormat can be used, but a more advanced programmatic technique is available via the builder classes.