* The rules model all the historic and future transitions for a time-zone. * {@link ZoneOffsetTransition} is used for known transitions, typically historic. * {@link ZoneOffsetTransitionRule} is used for future transitions that are based * on the result of an algorithm. *
* The rules are loaded via {@link ZoneRulesProvider} using a {@link ZoneId}. * The same rules may be shared internally between multiple zone IDs. *
* Serializing an instance of {@code 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. * *
* The returned rules always have the same offset. * * @param offset the offset, not null * @return the zone rules, not null */ public static ZoneRules of(ZoneOffset offset) { Jdk8Methods.requireNonNull(offset, "offset"); return new Fixed(offset); } /** * Restricted constructor. */ ZoneRules() { } //----------------------------------------------------------------------- /** * Checks of the zone rules are fixed, such that the offset never varies. * * @return true if the time-zone is fixed and the offset never changes */ public abstract boolean isFixedOffset(); //----------------------------------------------------------------------- /** * 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. * * @param 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 * @return the offset, not null */ public abstract ZoneOffset getOffset(Instant instant); /** * 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)}. * * @param localDateTime the local date-time to query, not null, but null * may be ignored if the rules have a single offset for all instants * @return the best available offset for the local date-time, not null */ public abstract ZoneOffset getOffset(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: *
* 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 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.
*
* @param 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
* @return the list of valid offsets, may be immutable, not null
*/
public abstract List
* 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:
*
* 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.
*
* @param 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
* @return the standard offset, not null
*/
public abstract ZoneOffset getStandardOffset(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.
*
* @param 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
* @return the difference between the standard and actual offset, not null
*/
public abstract Duration getDaylightSavings(Instant instant);
// default {
// ZoneOffset standardOffset = getStandardOffset(instant);
// ZoneOffset actualOffset = getOffset(instant);
// return actualOffset.toDuration().minus(standardOffset.toDuration()).normalized();
// }
/**
* Checks if the specified instant is in daylight savings.
*
* This checks if the standard and actual offsets are the same at the specified instant.
*
* @param 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
* @return the standard offset, not null
*/
public abstract boolean isDaylightSavings(Instant instant);
// default {
// return (getStandardOffset(instant).equals(getOffset(instant)) == false);
// }
/**
* 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.
*
* @param localDateTime the date-time to check, not null, but null
* may be ignored if the rules have a single offset for all instants
* @param offset the offset to check, null returns false
* @return true if the offset date-time is valid for these rules
*/
public abstract boolean isValidOffset(LocalDateTime localDateTime, ZoneOffset offset);
// default {
// return getValidOffsets(dateTime).contains(offset);
// }
//-----------------------------------------------------------------------
/**
* 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.
*
* @param 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
* @return the next transition after the specified instant, null if this is after the last transition
*/
public abstract ZoneOffsetTransition nextTransition(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.
*
* @param 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
* @return the previous transition after the specified instant, null if this is before the first transition
*/
public abstract ZoneOffsetTransition previousTransition(Instant instant);
/**
* Gets the complete list of fully defined transitions.
*
* The complete set of transitions for this rules instance is defined by this method
* and {@link #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.
*
* @return an immutable list of fully defined transitions, not null
*/
public abstract List
* The complete set of transitions for this rules instance is defined by this method
* and {@link #getTransitions()}. This method returns instances of {@link ZoneOffsetTransitionRule}
* that define an algorithm for when transitions will occur.
*
* For any given {@code 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.
*
* @return an immutable list of transition rules, not null
*/
public abstract List
* 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.
*
* @param otherRules the other rules, null returns false
* @return true if this rules is the same as that specified
*/
@Override
public abstract boolean equals(Object otherRules);
/**
* Returns a suitable hash code given the definition of {@code #equals}.
*
* @return the hash code
*/
@Override
public abstract int hashCode();
//-----------------------------------------------------------------------
/**
* Fixed time-zone.
*/
static final class Fixed extends ZoneRules implements Serializable {
/** A serialization identifier for this class. */
private static final long serialVersionUID = -8733721350312276297L;
/** The offset. */
private final ZoneOffset offset;
/**
* Constructor.
*
* @param offset the offset, not null
*/
Fixed(ZoneOffset offset) {
this.offset = offset;
}
//-------------------------------------------------------------------------
@Override
public boolean isFixedOffset() {
return true;
}
@Override
public ZoneOffset getOffset(Instant instant) {
return offset;
}
@Override
public ZoneOffset getOffset(LocalDateTime localDateTime) {
return offset;
}
@Override
public List
*
* 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);
* }
*
*
* @param 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
* @return the offset transition, null if the local date-time is not in transition
*/
public abstract ZoneOffsetTransition getTransition(LocalDateTime localDateTime);
//-----------------------------------------------------------------------
/**
* Gets the standard offset for the specified instant in this zone.
*