ZoneRules.java
/*
* Copyright (c) 2007-present, Stephen Colebourne & Michael Nascimento Santos
*
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* * Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
*
* * Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* * Neither the name of JSR-310 nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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package org.threeten.bp.zone;
import java.io.Serializable;
import java.util.Collections;
import java.util.List;
import org.threeten.bp.Duration;
import org.threeten.bp.Instant;
import org.threeten.bp.LocalDateTime;
import org.threeten.bp.ZoneId;
import org.threeten.bp.ZoneOffset;
import org.threeten.bp.jdk8.Jdk8Methods;
/**
* The rules defining how the zone offset varies for a single time-zone.
* <p>
* 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.
* <p>
* The rules are loaded via {@link ZoneRulesProvider} using a {@link ZoneId}.
* The same rules may be shared internally between multiple zone IDs.
* <p>
* 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.
* <p>
* 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.
*
* <h3>Specification for implementors</h3>
* The supplied implementations of this class are immutable and thread-safe.
*/
public abstract class ZoneRules {
/**
* Obtains an instance of {@code ZoneRules} with full transition rules.
*
* @param baseStandardOffset the standard offset to use before legal rules were set, not null
* @param baseWallOffset the wall offset to use before legal rules were set, not null
* @param standardOffsetTransitionList the list of changes to the standard offset, not null
* @param transitionList the list of transitions, not null
* @param lastRules the recurring last rules, size 16 or less, not null
* @return the zone rules, not null
*/
public static ZoneRules of(ZoneOffset baseStandardOffset,
ZoneOffset baseWallOffset,
List<ZoneOffsetTransition> standardOffsetTransitionList,
List<ZoneOffsetTransition> transitionList,
List<ZoneOffsetTransitionRule> lastRules) {
Jdk8Methods.requireNonNull(baseStandardOffset, "baseStandardOffset");
Jdk8Methods.requireNonNull(baseWallOffset, "baseWallOffset");
Jdk8Methods.requireNonNull(standardOffsetTransitionList, "standardOffsetTransitionList");
Jdk8Methods.requireNonNull(transitionList, "transitionList");
Jdk8Methods.requireNonNull(lastRules, "lastRules");
return new StandardZoneRules(baseStandardOffset, baseWallOffset,
standardOffsetTransitionList, transitionList, lastRules);
}
/**
* Obtains an instance of {@code ZoneRules} that always uses the same offset.
* <p>
* 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.
* <p>
* 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.
* <p>
* The mapping from a local date-time to an offset is not straightforward.
* There are three cases:
* <p><ul>
* <li>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.</li>
* <li>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.</li>
* <li>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.</li>
* </ul><p>
* 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.
* <p>
* 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.
* <p>
* The mapping from a local date-time to an offset is not straightforward.
* There are three cases:
* <p><ul>
* <li>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.</li>
* <li>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.</li>
* <li>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.</li>
* </ul><p>
* 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.
* <p>
* There are various ways to handle the conversion from a {@code LocalDateTime}.
* One technique, using this method, would be:
* <pre>
* 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);
* }
* </pre>
* <p>
* 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<ZoneOffset> getValidOffsets(LocalDateTime localDateTime);
/**
* Gets the offset transition applicable at the specified local date-time in these rules.
* <p>
* The mapping from a local date-time to an offset is not straightforward.
* There are three cases:
* <p><ul>
* <li>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.</li>
* <li>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.</li>
* <li>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.</li>
* </ul><p>
* A transition is used to model the cases of a Gap or Overlap.
* The Normal case will return null.
* <p>
* There are various ways to handle the conversion from a {@code LocalDateTime}.
* One technique, using this method, would be:
* <pre>
* 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);
* }
* </pre>
*
* @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.
* <p>
* 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.
* <p>
* 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.
* <p>
* 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.
* <p>
* 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.
* <p>
* 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.
* <p>
* 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.
* <p>
* 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.
* <p>
* 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<ZoneOffsetTransition> getTransitions();
/**
* Gets the list of transition rules for years beyond those defined in the transition list.
* <p>
* 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.
* <p>
* 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.
* <p>
* 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.
* <p>
* 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<ZoneOffsetTransitionRule> getTransitionRules();
//-----------------------------------------------------------------------
/**
* Checks if this set of rules equals another.
* <p>
* 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.
* <p>
* 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<ZoneOffset> getValidOffsets(LocalDateTime localDateTime) {
return Collections.singletonList(offset);
}
@Override
public ZoneOffsetTransition getTransition(LocalDateTime localDateTime) {
return null;
}
@Override
public boolean isValidOffset(LocalDateTime dateTime, ZoneOffset offset) {
return this.offset.equals(offset);
}
//-------------------------------------------------------------------------
@Override
public ZoneOffset getStandardOffset(Instant instant) {
return offset;
}
@Override
public Duration getDaylightSavings(Instant instant) {
return Duration.ZERO;
}
@Override
public boolean isDaylightSavings(Instant instant) {
return false;
}
//-------------------------------------------------------------------------
@Override
public ZoneOffsetTransition nextTransition(Instant instant) {
return null;
}
@Override
public ZoneOffsetTransition previousTransition(Instant instant) {
return null;
}
@Override
public List<ZoneOffsetTransition> getTransitions() {
return Collections.emptyList();
}
@Override
public List<ZoneOffsetTransitionRule> getTransitionRules() {
return Collections.emptyList();
}
//-----------------------------------------------------------------------
@Override
public boolean equals(Object obj) {
if (this == obj) {
return true;
}
if (obj instanceof Fixed) {
return offset.equals(((Fixed) obj).offset);
}
if (obj instanceof StandardZoneRules) {
StandardZoneRules szr = (StandardZoneRules) obj;
return szr.isFixedOffset() && offset.equals(szr.getOffset(Instant.EPOCH));
}
return false;
}
@Override
public int hashCode() {
return 1 ^
(31 + offset.hashCode()) ^
1 ^
(31 + offset.hashCode()) ^
1;
}
@Override
public String toString() {
return "FixedRules:" + offset;
}
}
}