TzdbZoneRules

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.

Throw:

Checks if the specified instant is in daylight savings.

This checks if the standard and actual offsets are the same at the specified instant.

Throw:

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

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.

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.

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

The method is for javascript performance optimisation.

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.

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:

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, {@link #getValidOffsets(LocalDateTime)} and {@link #getTransition(LocalDateTime)}.

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.

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.

Needs tz data with standard offsets (field 7 of the packed format); throws for older data.

Throw:

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:

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 {@code 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);
 }

Not supported, always throws.

In java.time, this returns the recurring rules (such as "last Sunday in March") for the years after the list of {@link #transitions()}. The tzdb data of this package is expanded into explicit transitions through the year 2499 and has no such rules. Use #nextTransition or #previousTransition to iterate over the transitions.

Throw:

Not supported, always throws.

In java.time, the complete set of transitions is this list of the historic transitions together with {@link #transitionRules()} for the later years. The tzdb data of this package contains only explicit transitions through the year 2499 and doesn't say where the historic part ends, so it can't return what java.time returns. Use #nextTransition or #previousTransition to iterate over the transitions.

Throw:

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:

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 {@code 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.