added in API level 26

ZoneRules

public final class ZoneRules
extends Object implements Serializable

java.lang.Object
   ↳ java.time.zone.ZoneRules


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 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.

Summary

Public methods

boolean equals(Object otherRules)

Checks if this set of rules equals another.

Duration getDaylightSavings(Instant instant)

Gets the amount of daylight savings in use for the specified instant in this zone.

ZoneOffset getOffset(LocalDateTime localDateTime)

Gets a suitable offset for the specified local date-time in these rules.

ZoneOffset getOffset(Instant instant)

Gets the offset applicable at the specified instant in these rules.

ZoneOffset getStandardOffset(Instant instant)

Gets the standard offset for the specified instant in this zone.

ZoneOffsetTransition getTransition(LocalDateTime localDateTime)

Gets the offset transition applicable at the specified local date-time in these rules.

List<ZoneOffsetTransitionRule> getTransitionRules()

Gets the list of transition rules for years beyond those defined in the transition list.

List<ZoneOffsetTransition> getTransitions()

Gets the complete list of fully defined transitions.

List<ZoneOffset> getValidOffsets(LocalDateTime localDateTime)

Gets the offset applicable at the specified local date-time in these rules.

int hashCode()

Returns a suitable hash code given the definition of #equals.

boolean isDaylightSavings(Instant instant)

Checks if the specified instant is in daylight savings.

boolean isFixedOffset()

Checks of the zone rules are fixed, such that the offset never varies.

boolean isValidOffset(LocalDateTime localDateTime, ZoneOffset offset)

Checks if the offset date-time is valid for these rules.

ZoneOffsetTransition nextTransition(Instant instant)

Gets the next transition after the specified instant.

static ZoneRules of(ZoneOffset baseStandardOffset, ZoneOffset baseWallOffset, List<ZoneOffsetTransition> standardOffsetTransitionList, List<ZoneOffsetTransition> transitionList, List<ZoneOffsetTransitionRule> lastRules)

Obtains an instance of a ZoneRules.

static ZoneRules of(ZoneOffset offset)

Obtains an instance of ZoneRules that has fixed zone rules.

ZoneOffsetTransition previousTransition(Instant instant)

Gets the previous transition before the specified instant.

String toString()

Returns a string describing this object.

Inherited methods

Public methods

equals

added in API level 26
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.

Parameters
otherRules Object: the other rules, null returns false

Returns
boolean true if this rules is the same as that specified

getDaylightSavings

added in API level 26
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.

This default implementation calculates the duration from the actual and standard offsets.

Parameters
instant 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
Duration the difference between the standard and actual offset, not null

getOffset

added in API level 26
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) and getTransition(LocalDateTime).

Parameters
localDateTime 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
ZoneOffset the best available offset for the local date-time, not null

getOffset

added in API level 26
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 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
ZoneOffset the offset, not null

getStandardOffset

added in API level 26
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 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
ZoneOffset the standard offset, not null

getTransition

added in API level 26
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 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
ZoneOffsetTransition the offset transition, null if the local date-time is not in transition

getTransitionRules

added in API level 26
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 of ZoneOffsetTransitionRule 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
List<ZoneOffsetTransitionRule> an immutable list of transition rules, not null

getTransitions

added in API level 26
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
List<ZoneOffsetTransition> an immutable list of fully defined transitions, not null

getValidOffsets

added in API level 26
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<ZoneOffset> 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 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
List<ZoneOffset> the list of valid offsets, may be immutable, not null

hashCode

added in API level 26
int hashCode ()

Returns a suitable hash code given the definition of #equals.

Returns
int the hash code

isDaylightSavings

added in API level 26
boolean isDaylightSavings (Instant instant)

Checks if the specified instant is in daylight savings.

This checks if the standard offset and the actual offset are the same for the specified instant. If they are not, it is assumed that daylight savings is in operation.

This default implementation compares the actual and standard offsets.

Parameters
instant 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
boolean the standard offset, not null

isFixedOffset

added in API level 26
boolean isFixedOffset ()

Checks of the zone rules are fixed, such that the offset never varies.

Returns
boolean true if the time-zone is fixed and the offset never changes

isValidOffset

added in API level 26
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 one of the valid offsets.

This default implementation checks if getValidOffsets(java.time.LocalDateTime) contains the specified offset.

Parameters
localDateTime LocalDateTime: the date-time to check, not null, but null may be ignored if the rules have a single offset for all instants

offset ZoneOffset: the offset to check, null returns false

Returns
boolean true if the offset date-time is valid for these rules

nextTransition

added in API level 26
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 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
ZoneOffsetTransition the next transition after the specified instant, null if this is after the last transition

of

added in API level 26
ZoneRules of (ZoneOffset baseStandardOffset, 
                ZoneOffset baseWallOffset, 
                List<ZoneOffsetTransition> standardOffsetTransitionList, 
                List<ZoneOffsetTransition> transitionList, 
                List<ZoneOffsetTransitionRule> lastRules)

Obtains an instance of a ZoneRules.

Parameters
baseStandardOffset ZoneOffset: the standard offset to use before legal rules were set, not null

baseWallOffset ZoneOffset: the wall offset to use before legal rules were set, not null

standardOffsetTransitionList List: the list of changes to the standard offset, not null

transitionList List: the list of transitions, not null

lastRules List: the recurring last rules, size 16 or less, not null

Returns
ZoneRules the zone rules, not null

of

added in API level 26
ZoneRules of (ZoneOffset offset)

Obtains an instance of ZoneRules that has fixed zone rules.

Parameters
offset ZoneOffset: the offset this fixed zone rules is based on, not null

Returns
ZoneRules the zone rules, not null

See also:

previousTransition

added in API level 26
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 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
ZoneOffsetTransition the previous transition after the specified instant, null if this is before the first transition

toString

added in API level 26
String toString ()

Returns a string describing this object.

Returns
String a string for debugging, not null