Class DateTimeZone
- Direct Known Subclasses:
StorableDateTimeZone
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 following 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.
Unless you override the standard behaviour, the default if the third approach.
DateTimeZone is thread-safe and immutable, and all subclasses must be as well.
- Since:
- 1.0
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Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionlong
adjustOffset
(long instant, boolean earlierOrLater) Adjusts the offset to be the earlier or later one during an overlap.abstract ZoneRules
long
convertLocalToUTC
(long instantLocal, boolean strict) Converts a local instant to a standard UTC instant with the same local time.long
convertLocalToUTC
(long instantLocal, boolean strict, long originalInstantUTC) Converts a local instant to a standard UTC instant with the same local time attempting to use the same offset as the original.long
convertUTCToLocal
(long instantUTC) Converts a standard UTC instant to a local instant with the same local time.final String
getID()
Gets the ID of this datetime zone.long
getMillisKeepLocal
(DateTimeZone newZone, long oldInstant) Gets the millisecond instant in another zone keeping the same local time.abstract int
getOffset
(long instant) Gets the millisecond offset to add to UTC to get local time.int
getOffsetFromLocal
(long instantLocal) Gets the millisecond offset to subtract from local time to get UTC time.abstract int
getStandardOffset
(long instant) Gets the standard millisecond offset to add to UTC to get local time, when standard time is in effect.abstract boolean
isFixed()
Returns true if this time zone has no transitions.boolean
isStandardOffset
(long instant) Checks whether, at a particular instant, the offset is standard or not.abstract long
nextTransition
(long instant) Advances the given instant to where the time zone offset or name changes.abstract long
previousTransition
(long instant) Retreats the given instant to where the time zone offset or name changes.
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Constructor Details
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DateTimeZone
Constructor.- Parameters:
id
- the id to use- Throws:
IllegalArgumentException
- if the id is null
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Method Details
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getID
Gets the ID of this datetime zone.- Returns:
- the ID of this datetime zone
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getOffset
public abstract int getOffset(long instant) Gets the millisecond offset to add to UTC to get local time.- Parameters:
instant
- milliseconds from 1970-01-01T00:00:00Z to get the offset for- Returns:
- the millisecond offset to add to UTC to get local time
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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.- Parameters:
instant
- milliseconds from 1970-01-01T00:00:00Z to get the offset for- Returns:
- the millisecond offset to add to UTC to get local time
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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)
equalsgetStandardOffset(long)
at the specified instant.- Parameters:
instant
- milliseconds from 1970-01-01T00:00:00Z to get the offset for- Returns:
- true if the offset at the given instant is the standard offset
- Since:
- 1.5
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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.For overlaps (where the local time is ambiguous), this method returns the offset applicable before the gap. The effect of this is that any instant calculated using the offset from an overlap will be in "summer" time.
For gaps, this method returns the offset applicable before the gap, ie "winter" offset. However, the effect of this is that any instant calculated using the offset from a gap will be after the gap, in "summer" time.
For example, consider a zone with a gap from 01:00 to 01:59:
Input: 00:00 (before gap) Output: Offset applicable before gap DateTime: 00:00
Input: 00:30 (before gap) Output: Offset applicable before gap DateTime: 00:30
Input: 01:00 (in gap) Output: Offset applicable before gap DateTime: 02:00
Input: 01:30 (in gap) Output: Offset applicable before gap DateTime: 02:30
Input: 02:00 (after gap) Output: Offset applicable after gap DateTime: 02:00
Input: 02:30 (after gap) Output: Offset applicable after gap DateTime: 02:30
NOTE: Prior to v2.0, the DST overlap behaviour was not defined and varied by hemisphere. Prior to v1.5, the DST gap behaviour was also not defined. In v2.4, the documentation was clarified again.
- Parameters:
instantLocal
- the millisecond instant, relative to this time zone, to get the offset for- Returns:
- the millisecond offset to subtract from local time to get UTC time
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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.- Parameters:
instantUTC
- the UTC instant to convert to local- Returns:
- the local instant with the same local time
- Throws:
ArithmeticException
- if the result overflows a long- Since:
- 1.5
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convertLocalToUTC
public long convertLocalToUTC(long instantLocal, boolean strict, long originalInstantUTC) Converts a local instant to a standard UTC instant with the same local time attempting to use the same offset as the original.This conversion is used after performing a calculation where the calculation was done using a simple local zone. Whenever possible, the same offset as the original offset will be used. This is most significant during a daylight savings overlap.
- Parameters:
instantLocal
- the local instant to convert to UTCstrict
- whether the conversion should reject non-existent local timesoriginalInstantUTC
- the original instant that the calculation is based on- Returns:
- the UTC instant with the same local time,
- Throws:
ArithmeticException
- if the result overflows a longIllegalArgumentException
- if the zone has no equivalent local time- Since:
- 2.0
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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.- Parameters:
instantLocal
- the local instant to convert to UTCstrict
- whether the conversion should reject non-existent local times- Returns:
- the UTC instant with the same local time,
- Throws:
ArithmeticException
- if the result overflows a long- Since:
- 1.5
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getMillisKeepLocal
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.
- Parameters:
newZone
- the new zone, null means defaultoldInstant
- the UTC millisecond instant to convert- Returns:
- the UTC millisecond instant with the same local time in the new zone
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adjustOffset
public long adjustOffset(long instant, boolean earlierOrLater) Adjusts the offset to be the earlier or later one during an overlap.- Parameters:
instant
- the instant to adjustearlierOrLater
- false for earlier, true for later- Returns:
- the adjusted instant millis
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isFixed
public abstract boolean isFixed()Returns true if this time zone has no transitions.- Returns:
- true if no transitions
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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.- Parameters:
instant
- milliseconds from 1970-01-01T00:00:00Z- Returns:
- milliseconds from 1970-01-01T00:00:00Z
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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.- Parameters:
instant
- milliseconds from 1970-01-01T00:00:00Z- Returns:
- milliseconds from 1970-01-01T00:00:00Z
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asZoneRules
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