Class ZoneRules
- java.lang.Object
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- org.threeten.bp.zone.ZoneRules
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public abstract class ZoneRules extends Object
The rules defining how the zone offset varies for a single time-zone.The rules model all the historic and future transitions for a time-zone.
ZoneOffsetTransition
is used for known transitions, typically historic.ZoneOffsetTransitionRule
is used for future transitions that are based on the result of an algorithm.The rules are loaded via
ZoneRulesProvider
using aZoneId
. The same rules may be shared internally between multiple zone IDs.Serializing an instance of
ZoneRules
will store the entire set of rules. It does not store the zone ID as it is not part of the state of this object.A rule implementation may or may not store full information about historic and future transitions, and the information stored is only as accurate as that supplied to the implementation by the rules provider. Applications should treat the data provided as representing the best information available to the implementation of this rule.
Specification for implementors
The supplied implementations of this class are immutable and thread-safe.
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Method Summary
All Methods Static Methods Instance Methods Abstract Methods Concrete Methods Modifier and Type Method Description abstract boolean
equals(Object otherRules)
Checks if this set of rules equals another.abstract Duration
getDaylightSavings(Instant instant)
Gets the amount of daylight savings in use for the specified instant in this zone.abstract ZoneOffset
getOffset(Instant instant)
Gets the offset applicable at the specified instant in these rules.abstract ZoneOffset
getOffset(LocalDateTime localDateTime)
Gets a suitable offset for the specified local date-time in these rules.abstract ZoneOffset
getStandardOffset(Instant instant)
Gets the standard offset for the specified instant in this zone.abstract ZoneOffsetTransition
getTransition(LocalDateTime localDateTime)
Gets the offset transition applicable at the specified local date-time in these rules.abstract List<ZoneOffsetTransitionRule>
getTransitionRules()
Gets the list of transition rules for years beyond those defined in the transition list.abstract List<ZoneOffsetTransition>
getTransitions()
Gets the complete list of fully defined transitions.abstract List<ZoneOffset>
getValidOffsets(LocalDateTime localDateTime)
Gets the offset applicable at the specified local date-time in these rules.abstract int
hashCode()
Returns a suitable hash code given the definition of#equals
.abstract boolean
isDaylightSavings(Instant instant)
Checks if the specified instant is in daylight savings.abstract boolean
isFixedOffset()
Checks of the zone rules are fixed, such that the offset never varies.abstract boolean
isValidOffset(LocalDateTime localDateTime, ZoneOffset offset)
Checks if the offset date-time is valid for these rules.abstract ZoneOffsetTransition
nextTransition(Instant instant)
Gets the next transition after the specified instant.static ZoneRules
of(ZoneOffset offset)
Obtains an instance ofZoneRules
that always uses the same offset.static ZoneRules
of(ZoneOffset baseStandardOffset, ZoneOffset baseWallOffset, List<ZoneOffsetTransition> standardOffsetTransitionList, List<ZoneOffsetTransition> transitionList, List<ZoneOffsetTransitionRule> lastRules)
Obtains an instance ofZoneRules
with full transition rules.abstract ZoneOffsetTransition
previousTransition(Instant instant)
Gets the previous transition before the specified instant.
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Method Detail
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of
public static ZoneRules of(ZoneOffset baseStandardOffset, ZoneOffset baseWallOffset, List<ZoneOffsetTransition> standardOffsetTransitionList, List<ZoneOffsetTransition> transitionList, List<ZoneOffsetTransitionRule> lastRules)
Obtains an instance ofZoneRules
with full transition rules.- Parameters:
baseStandardOffset
- the standard offset to use before legal rules were set, not nullbaseWallOffset
- the wall offset to use before legal rules were set, not nullstandardOffsetTransitionList
- the list of changes to the standard offset, not nulltransitionList
- the list of transitions, not nulllastRules
- the recurring last rules, size 16 or less, not null- Returns:
- the zone rules, not null
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of
public static ZoneRules of(ZoneOffset offset)
Obtains an instance ofZoneRules
that always uses the same offset.The returned rules always have the same offset.
- Parameters:
offset
- the offset, not null- Returns:
- the zone rules, not null
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isFixedOffset
public abstract boolean isFixedOffset()
Checks of the zone rules are fixed, such that the offset never varies.- Returns:
- true if the time-zone is fixed and the offset never changes
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getOffset
public abstract ZoneOffset getOffset(Instant instant)
Gets the offset applicable at the specified instant in these rules.The mapping from an instant to an offset is simple, there is only one valid offset for each instant. This method returns that offset.
- Parameters:
instant
- the instant to find the offset for, not null, but null may be ignored if the rules have a single offset for all instants- Returns:
- the offset, not null
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getOffset
public abstract ZoneOffset getOffset(LocalDateTime localDateTime)
Gets a suitable offset for the specified local date-time in these rules.The mapping from a local date-time to an offset is not straightforward. There are three cases:
- Normal, with one valid offset. For the vast majority of the year, the normal case applies, where there is a single valid offset for the local date-time.
- Gap, with zero valid offsets. This is when clocks jump forward typically due to the spring daylight savings change from "winter" to "summer". In a gap there are local date-time values with no valid offset.
- Overlap, with two valid offsets. This is when clocks are set back typically due to the autumn daylight savings change from "summer" to "winter". In an overlap there are local date-time values with two valid offsets.
Thus, for any given local date-time there can be zero, one or two valid offsets. This method returns the single offset in the Normal case, and in the Gap or Overlap case it returns the offset before the transition.
Since, in the case of Gap and Overlap, the offset returned is a "best" value, rather than the "correct" value, it should be treated with care. Applications that care about the correct offset should use a combination of this method,
getValidOffsets(LocalDateTime)
andgetTransition(LocalDateTime)
.- Parameters:
localDateTime
- the local date-time to query, not null, but null may be ignored if the rules have a single offset for all instants- Returns:
- the best available offset for the local date-time, not null
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getValidOffsets
public abstract List<ZoneOffset> getValidOffsets(LocalDateTime localDateTime)
Gets the offset applicable at the specified local date-time in these rules.The mapping from a local date-time to an offset is not straightforward. There are three cases:
- Normal, with one valid offset. For the vast majority of the year, the normal case applies, where there is a single valid offset for the local date-time.
- Gap, with zero valid offsets. This is when clocks jump forward typically due to the spring daylight savings change from "winter" to "summer". In a gap there are local date-time values with no valid offset.
- Overlap, with two valid offsets. This is when clocks are set back typically due to the autumn daylight savings change from "summer" to "winter". In an overlap there are local date-time values with two valid offsets.
Thus, for any given local date-time there can be zero, one or two valid offsets. This method returns that list of valid offsets, which is a list of size 0, 1 or 2. In the case where there are two offsets, the earlier offset is returned at index 0 and the later offset at index 1.
There are various ways to handle the conversion from a
LocalDateTime
. One technique, using this method, would be:List
validOffsets = rules.getOffset(localDT); if (validOffsets.size() == 1) { // Normal case: only one valid offset zoneOffset = validOffsets.get(0); } else { // Gap or Overlap: determine what to do from transition (which will be non-null) ZoneOffsetTransition trans = rules.getTransition(localDT); } In theory, it is possible for there to be more than two valid offsets. This would happen if clocks to be put back more than once in quick succession. This has never happened in the history of time-zones and thus has no special handling. However, if it were to happen, then the list would return more than 2 entries.
- Parameters:
localDateTime
- the local date-time to query for valid offsets, not null, but null may be ignored if the rules have a single offset for all instants- Returns:
- the list of valid offsets, may be immutable, not null
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getTransition
public abstract ZoneOffsetTransition getTransition(LocalDateTime localDateTime)
Gets the offset transition applicable at the specified local date-time in these rules.The mapping from a local date-time to an offset is not straightforward. There are three cases:
- Normal, with one valid offset. For the vast majority of the year, the normal case applies, where there is a single valid offset for the local date-time.
- Gap, with zero valid offsets. This is when clocks jump forward typically due to the spring daylight savings change from "winter" to "summer". In a gap there are local date-time values with no valid offset.
- Overlap, with two valid offsets. This is when clocks are set back typically due to the autumn daylight savings change from "summer" to "winter". In an overlap there are local date-time values with two valid offsets.
A transition is used to model the cases of a Gap or Overlap. The Normal case will return null.
There are various ways to handle the conversion from a
LocalDateTime
. One technique, using this method, would be:ZoneOffsetTransition trans = rules.getTransition(localDT); if (trans == null) { // Gap or Overlap: determine what to do from transition } else { // Normal case: only one valid offset zoneOffset = rule.getOffset(localDT); }
- Parameters:
localDateTime
- the local date-time to query for offset transition, not null, but null may be ignored if the rules have a single offset for all instants- Returns:
- the offset transition, null if the local date-time is not in transition
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getStandardOffset
public abstract ZoneOffset getStandardOffset(Instant instant)
Gets the standard offset for the specified instant in this zone.This provides access to historic information on how the standard offset has changed over time. The standard offset is the offset before any daylight saving time is applied. This is typically the offset applicable during winter.
- Parameters:
instant
- the instant to find the offset information for, not null, but null may be ignored if the rules have a single offset for all instants- Returns:
- the standard offset, not null
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getDaylightSavings
public abstract Duration getDaylightSavings(Instant instant)
Gets the amount of daylight savings in use for the specified instant in this zone.This provides access to historic information on how the amount of daylight savings has changed over time. This is the difference between the standard offset and the actual offset. Typically the amount is zero during winter and one hour during summer. Time-zones are second-based, so the nanosecond part of the duration will be zero.
- Parameters:
instant
- the instant to find the daylight savings for, not null, but null may be ignored if the rules have a single offset for all instants- Returns:
- the difference between the standard and actual offset, not null
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isDaylightSavings
public abstract boolean isDaylightSavings(Instant instant)
Checks if the specified instant is in daylight savings.This checks if the standard and actual offsets are the same at the specified instant.
- Parameters:
instant
- the instant to find the offset information for, not null, but null may be ignored if the rules have a single offset for all instants- Returns:
- the standard offset, not null
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isValidOffset
public abstract boolean isValidOffset(LocalDateTime localDateTime, ZoneOffset offset)
Checks if the offset date-time is valid for these rules.To be valid, the local date-time must not be in a gap and the offset must match the valid offsets.
- Parameters:
localDateTime
- the date-time to check, not null, but null may be ignored if the rules have a single offset for all instantsoffset
- the offset to check, null returns false- Returns:
- true if the offset date-time is valid for these rules
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nextTransition
public abstract ZoneOffsetTransition nextTransition(Instant instant)
Gets the next transition after the specified instant.This returns details of the next transition after the specified instant. For example, if the instant represents a point where "Summer" daylight savings time applies, then the method will return the transition to the next "Winter" time.
- Parameters:
instant
- the instant to get the next transition after, not null, but null may be ignored if the rules have a single offset for all instants- Returns:
- the next transition after the specified instant, null if this is after the last transition
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previousTransition
public abstract ZoneOffsetTransition previousTransition(Instant instant)
Gets the previous transition before the specified instant.This returns details of the previous transition after the specified instant. For example, if the instant represents a point where "summer" daylight saving time applies, then the method will return the transition from the previous "winter" time.
- Parameters:
instant
- the instant to get the previous transition after, not null, but null may be ignored if the rules have a single offset for all instants- Returns:
- the previous transition after the specified instant, null if this is before the first transition
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getTransitions
public abstract List<ZoneOffsetTransition> getTransitions()
Gets the complete list of fully defined transitions.The complete set of transitions for this rules instance is defined by this method and
getTransitionRules()
. This method returns those transitions that have been fully defined. These are typically historical, but may be in the future.The list will be empty for fixed offset rules and for any time-zone where there has only ever been a single offset. The list will also be empty if the transition rules are unknown.
- Returns:
- an immutable list of fully defined transitions, not null
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getTransitionRules
public abstract List<ZoneOffsetTransitionRule> getTransitionRules()
Gets the list of transition rules for years beyond those defined in the transition list.The complete set of transitions for this rules instance is defined by this method and
getTransitions()
. This method returns instances ofZoneOffsetTransitionRule
that define an algorithm for when transitions will occur.For any given
ZoneRules
, this list contains the transition rules for years beyond those years that have been fully defined. These rules typically refer to future daylight saving time rule changes.If the zone defines daylight savings into the future, then the list will normally be of size two and hold information about entering and exiting daylight savings. If the zone does not have daylight savings, or information about future changes is uncertain, then the list will be empty.
The list will be empty for fixed offset rules and for any time-zone where there is no daylight saving time. The list will also be empty if the transition rules are unknown.
- Returns:
- an immutable list of transition rules, not null
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equals
public abstract boolean equals(Object otherRules)
Checks if this set of rules equals another.Two rule sets are equal if they will always result in the same output for any given input instant or local date-time. Rules from two different groups may return false even if they are in fact the same.
This definition should result in implementations comparing their entire state.
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