DateTimeZone represents a time zone.
A time zone is a system of rules to convert time from one geographic
location to another. For example, Paris, France is one hour ahead of
London, England. Thus when it is 10:00 in London, it is 11:00 in Paris.
All time zone rules are expressed, for historical reasons, relative to
Greenwich, London. Local time in Greenwich is referred to as Greenwich Mean
Time (GMT). This is similar, but not precisely identical, to Universal
Coordinated Time, or UTC. This library only uses the term UTC.
Using this system, America/Los_Angeles is expressed as UTC-08:00, or UTC-07:00
in the summer. The offset -08:00 indicates that America/Los_Angeles time is
obtained from UTC by adding -08:00, that is, by subtracting 8 hours.
The offset differs in the summer because of daylight saving time, or DST.
The folowing definitions of time are generally used:
- UTC - The reference time.
- Standard Time - The local time without a daylight saving time offset.
For example, in Paris, standard time is UTC+01:00.
- Daylight Saving Time - The local time with a daylight saving time
offset. This offset is typically one hour, but not always. It is typically
used in most countries away from the equator. In Paris, daylight saving
time is UTC+02:00.
- Wall Time - This is what a local clock on the wall reads. This will be
either Standard Time or Daylight Saving Time depending on the time of year
and whether the location uses Daylight Saving Time.
Unlike the Java TimeZone class, DateTimeZone is immutable. It also only
supports long format time zone ids. Thus EST and ECT are not accepted.
However, the factory that accepts a TimeZone will attempt to convert from
the old short id to a suitable long id.
DateTimeZone is thread-safe and immutable, and all subclasses must be as
well.
convertLocalToUTC
public long convertLocalToUTC(long instantLocal,
boolean strict)
Converts a local instant to a standard UTC instant with the same
local time. This conversion is used after performing a calculation
where the calculation was done using a simple local zone.
instantLocal
- the local instant to convert to UTCstrict
- whether the conversion should reject non-existent local times
- the UTC instant with the same local time,
convertUTCToLocal
public long convertUTCToLocal(long instantUTC)
Converts a standard UTC instant to a local instant with the same
local time. This conversion is used before performing a calculation
so that the calculation can be done using a simple local zone.
instantUTC
- the UTC instant to convert to local
- the local instant with the same local time
equals
public abstract boolean equals(Object object)
Compare this datetime zone with another.
object
- the object to compare with
- true if equal, based on the ID and all internal rules
forID
public static DateTimeZone forID(String id)
Gets a time zone instance for the specified time zone id.
The time zone id may be one of those returned by getAvailableIDs.
Short ids, as accepted by
java.util.TimeZone
, are not accepted.
All IDs must be specified in the long format.
The exception is UTC, which is an acceptable id.
Alternatively a locale independent, fixed offset, datetime zone can
be specified. The form
[+-]hh:mm
can be used.
id
- the ID of the datetime zone, null means default
- the DateTimeZone object for the ID
forOffsetHours
public static DateTimeZone forOffsetHours(int hoursOffset)
throws IllegalArgumentException
Gets a time zone instance for the specified offset to UTC in hours.
This method assumes standard length hours.
This factory is a convenient way of constructing zones with a fixed offset.
hoursOffset
- the offset in hours from UTC
- the DateTimeZone object for the offset
forOffsetHoursMinutes
public static DateTimeZone forOffsetHoursMinutes(int hoursOffset,
int minutesOffset)
throws IllegalArgumentException
Gets a time zone instance for the specified offset to UTC in hours and minutes.
This method assumes 60 minutes in an hour, and standard length minutes.
This factory is a convenient way of constructing zones with a fixed offset.
The minutes value is always positive and in the range 0 to 59.
If constructed with the values (-2, 30), the resultiong zone is '-02:30'.
hoursOffset
- the offset in hours from UTCminutesOffset
- the offset in minutes from UTC, must be between 0 and 59 inclusive
- the DateTimeZone object for the offset
forOffsetMillis
public static DateTimeZone forOffsetMillis(int millisOffset)
Gets a time zone instance for the specified offset to UTC in milliseconds.
millisOffset
- the offset in millis from UTC
- the DateTimeZone object for the offset
forTimeZone
public static DateTimeZone forTimeZone(TimeZone zone)
Gets a time zone instance for a JDK TimeZone.
DateTimeZone only accepts a subset of the IDs from TimeZone. The
excluded IDs are the short three letter form (except UTC). This
method will attempt to convert between time zones created using the
short IDs and the full version.
This method is not designed to parse time zones with rules created by
applications using
SimpleTimeZone
directly.
zone
- the zone to convert, null means default
- the DateTimeZone object for the zone
getAvailableIDs
public static Set getAvailableIDs()
Gets all the available IDs supported.
- an unmodifiable Set of String IDs
getDefault
public static DateTimeZone getDefault()
Gets the default time zone.
- the default datetime zone object
getID
public final String getID()
Gets the ID of this datetime zone.
- the ID of this datetime zone
getMillisKeepLocal
public long getMillisKeepLocal(DateTimeZone newZone,
long oldInstant)
Gets the millisecond instant in another zone keeping the same local time.
The conversion is performed by converting the specified UTC millis to local
millis in this zone, then converting back to UTC millis in the new zone.
newZone
- the new zone, null means defaultoldInstant
- the UTC millisecond instant to convert
- the UTC millisecond instant with the same local time in the new zone
getName
public final String getName(long instant)
Gets the long name of this datetime zone suitable for display using
the default locale.
If the name is not available for the locale, then this method returns a
string in the format
[+-]hh:mm
.
instant
- milliseconds from 1970-01-01T00:00:00Z to get the name for
- the human-readable long name in the default locale
getName
public String getName(long instant,
Locale locale)
Gets the long name of this datetime zone suitable for display using
the specified locale.
If the name is not available for the locale, then this method returns a
string in the format
[+-]hh:mm
.
instant
- milliseconds from 1970-01-01T00:00:00Z to get the name forlocale
- the locale to get the name for
- the human-readable long name in the specified locale
getNameKey
public abstract String getNameKey(long instant)
Returns a non-localized name that is unique to this time zone. It can be
combined with id to form a unique key for fetching localized names.
instant
- milliseconds from 1970-01-01T00:00:00Z to get the name for
- name key or null if id should be used for names
getNameProvider
public static NameProvider getNameProvider()
Gets the name provider factory.
The name provider is a pluggable instance factory that supplies the
names of each DateTimeZone.
getOffset
public abstract int getOffset(long instant)
Gets the millisecond offset to add to UTC to get local time.
instant
- milliseconds from 1970-01-01T00:00:00Z to get the offset for
- the millisecond offset to add to UTC to get local time
getOffset
public final int getOffset(ReadableInstant instant)
Gets the millisecond offset to add to UTC to get local time.
instant
- instant to get the offset for, null means now
- the millisecond offset to add to UTC to get local time
getOffsetFromLocal
public int getOffsetFromLocal(long instantLocal)
Gets the millisecond offset to subtract from local time to get UTC time.
This offset can be used to undo adding the offset obtained by getOffset.
millisLocal == millisUTC + getOffset(millisUTC)
millisUTC == millisLocal - getOffsetFromLocal(millisLocal)
NOTE: After calculating millisLocal, some error may be introduced. At
offset transitions (due to DST or other historical changes), ranges of
local times may map to different UTC times.
This method will return an offset suitable for calculating an instant
after any DST gap. For example, consider a zone with a cutover
from 01:00 to 01:59:
Input: 00:00 Output: 00:00
Input: 00:30 Output: 00:30
Input: 01:00 Output: 02:00
Input: 01:30 Output: 02:30
Input: 02:00 Output: 02:00
Input: 02:30 Output: 02:30
NOTE: The behaviour of this method changed in v1.5, with the emphasis
on returning a consistent result later along the time-line (shown above).
instantLocal
- the millisecond instant, relative to this time zone, to
get the offset for
- the millisecond offset to subtract from local time to get UTC time
getProvider
public static Provider getProvider()
Gets the zone provider factory.
The zone provider is a pluggable instance factory that supplies the
actual instances of DateTimeZone.
getShortName
public final String getShortName(long instant)
Gets the short name of this datetime zone suitable for display using
the default locale.
If the name is not available for the locale, then this method returns a
string in the format
[+-]hh:mm
.
instant
- milliseconds from 1970-01-01T00:00:00Z to get the name for
- the human-readable short name in the default locale
getShortName
public String getShortName(long instant,
Locale locale)
Gets the short name of this datetime zone suitable for display using
the specified locale.
If the name is not available for the locale, then this method returns a
string in the format
[+-]hh:mm
.
instant
- milliseconds from 1970-01-01T00:00:00Z to get the name forlocale
- the locale to get the name for
- the human-readable short name in the specified locale
getStandardOffset
public abstract int getStandardOffset(long instant)
Gets the standard millisecond offset to add to UTC to get local time,
when standard time is in effect.
instant
- milliseconds from 1970-01-01T00:00:00Z to get the offset for
- the millisecond offset to add to UTC to get local time
hashCode
public int hashCode()
Gets a hash code compatable with equals.
isFixed
public abstract boolean isFixed()
Returns true if this time zone has no transitions.
isLocalDateTimeGap
public boolean isLocalDateTimeGap(LocalDateTime localDateTime)
Checks if the given
LocalDateTime
is within a gap.
When switching from standard time to Daylight Savings Time there is
typically a gap where a clock hour is missing. This method identifies
whether the local datetime refers to such a gap.
localDateTime
- the time to check, not null
- true if the given datetime refers to a gap
isStandardOffset
public boolean isStandardOffset(long instant)
Checks whether, at a particular instant, the offset is standard or not.
This method can be used to determine whether Summer Time (DST) applies.
As a general rule, if the offset at the specified instant is standard,
then either Winter time applies, or there is no Summer Time. If the
instant is not standard, then Summer Time applies.
The implementation of the method is simply whether
getOffset(long)
equals
getStandardOffset(long)
at the specified instant.
instant
- milliseconds from 1970-01-01T00:00:00Z to get the offset for
- true if the offset at the given instant is the standard offset
nextTransition
public abstract long nextTransition(long instant)
Advances the given instant to where the time zone offset or name changes.
If the instant returned is exactly the same as passed in, then
no changes occur after the given instant.
instant
- milliseconds from 1970-01-01T00:00:00Z
- milliseconds from 1970-01-01T00:00:00Z
previousTransition
public abstract long previousTransition(long instant)
Retreats the given instant to where the time zone offset or name changes.
If the instant returned is exactly the same as passed in, then
no changes occur before the given instant.
instant
- milliseconds from 1970-01-01T00:00:00Z
- milliseconds from 1970-01-01T00:00:00Z
setDefault
public static void setDefault(DateTimeZone zone)
throws SecurityException
Sets the default time zone.
zone
- the default datetime zone object, must not be null
setNameProvider
public static void setNameProvider(NameProvider nameProvider)
throws SecurityException
Sets the name provider factory.
The name provider is a pluggable instance factory that supplies the
names of each DateTimeZone.
nameProvider
- provider to use, or null for default
setProvider
public static void setProvider(Provider provider)
throws SecurityException
Sets the zone provider factory.
The zone provider is a pluggable instance factory that supplies the
actual instances of DateTimeZone.
provider
- provider to use, or null for default
toString
public String toString()
Gets the datetime zone as a string, which is simply its ID.
toTimeZone
public TimeZone toTimeZone()
Get the datetime zone as a java.util.TimeZone
.
- the closest matching TimeZone object
writeReplace
protected Object writeReplace()
throws ObjectStreamException
By default, when DateTimeZones are serialized, only a "stub" object
referring to the id is written out. When the stub is read in, it
replaces itself with a DateTimeZone object.
- a stub object to go in the stream