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 * This file is available under and governed by the GNU General Public
 * License version 2 only, as published by the Free Software Foundation.
 * However, the following notice accompanied the original version of this
 * file:
 *
 * Copyright (c) 2009-2012, Stephen Colebourne & Michael Nascimento Santos
 *
 * All rights reserved.
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package java.time.zone;

import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
import java.io.InvalidObjectException;
import java.io.ObjectInputStream;
import java.io.Serializable;
import java.time.Duration;
import java.time.Instant;
import java.time.LocalDateTime;
import java.time.ZoneOffset;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.Objects;


A transition between two offsets caused by a discontinuity in the local time-line.

 A transition between two offsets is normally the result of a daylight savings cutover. The discontinuity is normally a gap in spring and an overlap in autumn. ZoneOffsetTransition models the transition between the two offsets. 
 Gaps occur where there are local date-times that simply do not exist. An example would be when the offset changes from +03:00 to +04:00. This might be described as 'the clocks will move forward one hour tonight at 1am'. 
 Overlaps occur where there are local date-times that exist twice. An example would be when the offset changes from +04:00 to +03:00. This might be described as 'the clocks will move back one hour tonight at 2am'. 
Implementation Requirements:
This class is immutable and thread-safe.
Since:1.8
/**
 * A transition between two offsets caused by a discontinuity in the local time-line.
 * <p>
 * A transition between two offsets is normally the result of a daylight savings cutover.
 * The discontinuity is normally a gap in spring and an overlap in autumn.
 * {@code ZoneOffsetTransition} models the transition between the two offsets.
 * <p>
 * Gaps occur where there are local date-times that simply do not exist.
 * An example would be when the offset changes from {@code +03:00} to {@code +04:00}.
 * This might be described as 'the clocks will move forward one hour tonight at 1am'.
 * <p>
 * Overlaps occur where there are local date-times that exist twice.
 * An example would be when the offset changes from {@code +04:00} to {@code +03:00}.
 * This might be described as 'the clocks will move back one hour tonight at 2am'.
 *
 * @implSpec
 * This class is immutable and thread-safe.
 *
 * @since 1.8
 */
public final class ZoneOffsetTransition
        implements Comparable<ZoneOffsetTransition>, Serializable {

    
Serialization version.

/**
     * Serialization version.
     */
    private static final long serialVersionUID = -6946044323557704546L;
    
The transition epoch-second.

/**
     * The transition epoch-second.
     */
    private final long epochSecond;
    
The local transition date-time at the transition.

/**
     * The local transition date-time at the transition.
     */
    private final LocalDateTime transition;
    
The offset before transition.

/**
     * The offset before transition.
     */
    private final ZoneOffset offsetBefore;
    
The offset after transition.

/**
     * The offset after transition.
     */
    private final ZoneOffset offsetAfter;

    //-----------------------------------------------------------------------
    
Obtains an instance defining a transition between two offsets.

 Applications should normally obtain an instance from ZoneRules. This factory is only intended for use when creating ZoneRules. 
Params:
  • transition –  the transition date-time at the transition, which never
 actually occurs, expressed local to the before offset, not null
  • offsetBefore –  the offset before the transition, not null
  • offsetAfter –  the offset at and after the transition, not null
Throws:
Returns:the transition, not null
/**
     * Obtains an instance defining a transition between two offsets.
     * <p>
     * Applications should normally obtain an instance from {@link ZoneRules}.
     * This factory is only intended for use when creating {@link ZoneRules}.
     *
     * @param transition  the transition date-time at the transition, which never
     *  actually occurs, expressed local to the before offset, not null
     * @param offsetBefore  the offset before the transition, not null
     * @param offsetAfter  the offset at and after the transition, not null
     * @return the transition, not null
     * @throws IllegalArgumentException if {@code offsetBefore} and {@code offsetAfter}
     *         are equal, or {@code transition.getNano()} returns non-zero value
     */
    public static ZoneOffsetTransition of(LocalDateTime transition, ZoneOffset offsetBefore, ZoneOffset offsetAfter) {
        Objects.requireNonNull(transition, "transition");
        Objects.requireNonNull(offsetBefore, "offsetBefore");
        Objects.requireNonNull(offsetAfter, "offsetAfter");
        if (offsetBefore.equals(offsetAfter)) {
            throw new IllegalArgumentException("Offsets must not be equal");
        }
        if (transition.getNano() != 0) {
            throw new IllegalArgumentException("Nano-of-second must be zero");
        }
        return new ZoneOffsetTransition(transition, offsetBefore, offsetAfter);
    }

    
Creates an instance defining a transition between two offsets.

Params:
  • transition –  the transition date-time with the offset before the transition, not null
  • offsetBefore –  the offset before the transition, not null
  • offsetAfter –  the offset at and after the transition, not null
/**
     * Creates an instance defining a transition between two offsets.
     *
     * @param transition  the transition date-time with the offset before the transition, not null
     * @param offsetBefore  the offset before the transition, not null
     * @param offsetAfter  the offset at and after the transition, not null
     */
    ZoneOffsetTransition(LocalDateTime transition, ZoneOffset offsetBefore, ZoneOffset offsetAfter) {
        assert transition.getNano() == 0;
        this.epochSecond = transition.toEpochSecond(offsetBefore);
        this.transition = transition;
        this.offsetBefore = offsetBefore;
        this.offsetAfter = offsetAfter;
    }

    
Creates an instance from epoch-second and offsets.

Params:
  • epochSecond –  the transition epoch-second
  • offsetBefore –  the offset before the transition, not null
  • offsetAfter –  the offset at and after the transition, not null
/**
     * Creates an instance from epoch-second and offsets.
     *
     * @param epochSecond  the transition epoch-second
     * @param offsetBefore  the offset before the transition, not null
     * @param offsetAfter  the offset at and after the transition, not null
     */
    ZoneOffsetTransition(long epochSecond, ZoneOffset offsetBefore, ZoneOffset offsetAfter) {
        this.epochSecond = epochSecond;
        this.transition = LocalDateTime.ofEpochSecond(epochSecond, 0, offsetBefore);
        this.offsetBefore = offsetBefore;
        this.offsetAfter = offsetAfter;
    }

    //-----------------------------------------------------------------------
    
Defend against malicious streams.

Params:
  • s – the stream to read
Throws:
/**
     * Defend against malicious streams.
     *
     * @param s the stream to read
     * @throws InvalidObjectException always
     */
    private void readObject(ObjectInputStream s) throws InvalidObjectException {
        throw new InvalidObjectException("Deserialization via serialization delegate");
    }

    
Writes the object using a
dedicated serialized form.

@serialData
Refer to the serialized form of
ZoneRules.writeReplace
for the encoding of epoch seconds and offsets.


  out.writeByte(2);                // identifies a ZoneOffsetTransition
  out.writeEpochSec(toEpochSecond);
  out.writeOffset(offsetBefore);
  out.writeOffset(offsetAfter);
 
Returns:the replacing object, not null
/**
     * Writes the object using a
     * <a href="../../../serialized-form.html#java.time.zone.Ser">dedicated serialized form</a>.
     * @serialData
     * Refer to the serialized form of
     * <a href="../../../serialized-form.html#java.time.zone.ZoneRules">ZoneRules.writeReplace</a>
     * for the encoding of epoch seconds and offsets.
     * <pre style="font-size:1.0em">{@code
     *
     *   out.writeByte(2);                // identifies a ZoneOffsetTransition
     *   out.writeEpochSec(toEpochSecond);
     *   out.writeOffset(offsetBefore);
     *   out.writeOffset(offsetAfter);
     * }
     * </pre>
     * @return the replacing object, not null
     */
    private Object writeReplace() {
        return new Ser(Ser.ZOT, this);
    }

    
Writes the state to the stream.

Params:
  • out –  the output stream, not null
Throws:
/**
     * Writes the state to the stream.
     *
     * @param out  the output stream, not null
     * @throws IOException if an error occurs
     */
    void writeExternal(DataOutput out) throws IOException {
        Ser.writeEpochSec(epochSecond, out);
        Ser.writeOffset(offsetBefore, out);
        Ser.writeOffset(offsetAfter, out);
    }

    
Reads the state from the stream.

Params:
  • in –  the input stream, not null
Throws:
Returns:the created object, not null
/**
     * Reads the state from the stream.
     *
     * @param in  the input stream, not null
     * @return the created object, not null
     * @throws IOException if an error occurs
     */
    static ZoneOffsetTransition readExternal(DataInput in) throws IOException {
        long epochSecond = Ser.readEpochSec(in);
        ZoneOffset before = Ser.readOffset(in);
        ZoneOffset after = Ser.readOffset(in);
        if (before.equals(after)) {
            throw new IllegalArgumentException("Offsets must not be equal");
        }
        return new ZoneOffsetTransition(epochSecond, before, after);
    }

    //-----------------------------------------------------------------------
    
Gets the transition instant.


This is the instant of the discontinuity, which is defined as the first
instant that the 'after' offset applies.

 The methods getInstant(), getDateTimeBefore() and getDateTimeAfter() all represent the same instant. 
Returns:the transition instant, not null
/**
     * Gets the transition instant.
     * <p>
     * This is the instant of the discontinuity, which is defined as the first
     * instant that the 'after' offset applies.
     * <p>
     * The methods {@link #getInstant()}, {@link #getDateTimeBefore()} and {@link #getDateTimeAfter()}
     * all represent the same instant.
     *
     * @return the transition instant, not null
     */
    public Instant getInstant() {
        return Instant.ofEpochSecond(epochSecond);
    }

    
Gets the transition instant as an epoch second.

Returns:the transition epoch second
/**
     * Gets the transition instant as an epoch second.
     *
     * @return the transition epoch second
     */
    public long toEpochSecond() {
        return epochSecond;
    }

    //-------------------------------------------------------------------------
    
Gets the local transition date-time, as would be expressed with the 'before' offset.


This is the date-time where the discontinuity begins expressed with the 'before' offset.
At this instant, the 'after' offset is actually used, therefore the combination of this
date-time and the 'before' offset will never occur.


The combination of the 'before' date-time and offset represents the same instant
as the 'after' date-time and offset.

Returns:the transition date-time expressed with the before offset, not null
/**
     * Gets the local transition date-time, as would be expressed with the 'before' offset.
     * <p>
     * This is the date-time where the discontinuity begins expressed with the 'before' offset.
     * At this instant, the 'after' offset is actually used, therefore the combination of this
     * date-time and the 'before' offset will never occur.
     * <p>
     * The combination of the 'before' date-time and offset represents the same instant
     * as the 'after' date-time and offset.
     *
     * @return the transition date-time expressed with the before offset, not null
     */
    public LocalDateTime getDateTimeBefore() {
        return transition;
    }

    
Gets the local transition date-time, as would be expressed with the 'after' offset.


This is the first date-time after the discontinuity, when the new offset applies.


The combination of the 'before' date-time and offset represents the same instant
as the 'after' date-time and offset.

Returns:the transition date-time expressed with the after offset, not null
/**
     * Gets the local transition date-time, as would be expressed with the 'after' offset.
     * <p>
     * This is the first date-time after the discontinuity, when the new offset applies.
     * <p>
     * The combination of the 'before' date-time and offset represents the same instant
     * as the 'after' date-time and offset.
     *
     * @return the transition date-time expressed with the after offset, not null
     */
    public LocalDateTime getDateTimeAfter() {
        return transition.plusSeconds(getDurationSeconds());
    }

    
Gets the offset before the transition.


This is the offset in use before the instant of the transition.

Returns:the offset before the transition, not null
/**
     * Gets the offset before the transition.
     * <p>
     * This is the offset in use before the instant of the transition.
     *
     * @return the offset before the transition, not null
     */
    public ZoneOffset getOffsetBefore() {
        return offsetBefore;
    }

    
Gets the offset after the transition.


This is the offset in use on and after the instant of the transition.

Returns:the offset after the transition, not null
/**
     * Gets the offset after the transition.
     * <p>
     * This is the offset in use on and after the instant of the transition.
     *
     * @return the offset after the transition, not null
     */
    public ZoneOffset getOffsetAfter() {
        return offsetAfter;
    }

    
Gets the duration of the transition.


In most cases, the transition duration is one hour, however this is not always the case.
The duration will be positive for a gap and negative for an overlap.
Time-zones are second-based, so the nanosecond part of the duration will be zero.

Returns:the duration of the transition, positive for gaps, negative for overlaps
/**
     * Gets the duration of the transition.
     * <p>
     * In most cases, the transition duration is one hour, however this is not always the case.
     * The duration will be positive for a gap and negative for an overlap.
     * Time-zones are second-based, so the nanosecond part of the duration will be zero.
     *
     * @return the duration of the transition, positive for gaps, negative for overlaps
     */
    public Duration getDuration() {
        return Duration.ofSeconds(getDurationSeconds());
    }

    
Gets the duration of the transition in seconds.

Returns:the duration in seconds
/**
     * Gets the duration of the transition in seconds.
     *
     * @return the duration in seconds
     */
    private int getDurationSeconds() {
        return getOffsetAfter().getTotalSeconds() - getOffsetBefore().getTotalSeconds();
    }

    
Does this transition represent a gap in the local time-line.

 Gaps occur where there are local date-times that simply do not exist. An example would be when the offset changes from +01:00 to +02:00. This might be described as 'the clocks will move forward one hour tonight at 1am'. 
Returns:true if this transition is a gap, false if it is an overlap
/**
     * Does this transition represent a gap in the local time-line.
     * <p>
     * Gaps occur where there are local date-times that simply do not exist.
     * An example would be when the offset changes from {@code +01:00} to {@code +02:00}.
     * This might be described as 'the clocks will move forward one hour tonight at 1am'.
     *
     * @return true if this transition is a gap, false if it is an overlap
     */
    public boolean isGap() {
        return getOffsetAfter().getTotalSeconds() > getOffsetBefore().getTotalSeconds();
    }

    
Does this transition represent an overlap in the local time-line.

 Overlaps occur where there are local date-times that exist twice. An example would be when the offset changes from +02:00 to +01:00. This might be described as 'the clocks will move back one hour tonight at 2am'. 
Returns:true if this transition is an overlap, false if it is a gap
/**
     * Does this transition represent an overlap in the local time-line.
     * <p>
     * Overlaps occur where there are local date-times that exist twice.
     * An example would be when the offset changes from {@code +02:00} to {@code +01:00}.
     * This might be described as 'the clocks will move back one hour tonight at 2am'.
     *
     * @return true if this transition is an overlap, false if it is a gap
     */
    public boolean isOverlap() {
        return getOffsetAfter().getTotalSeconds() < getOffsetBefore().getTotalSeconds();
    }

    
Checks if the specified offset is valid during this transition.


This checks to see if the given offset will be valid at some point in the transition.
A gap will always return false.
An overlap will return true if the offset is either the before or after offset.

Params:
  • offset –  the offset to check, null returns false
Returns:true if the offset is valid during the transition
/**
     * Checks if the specified offset is valid during this transition.
     * <p>
     * This checks to see if the given offset will be valid at some point in the transition.
     * A gap will always return false.
     * An overlap will return true if the offset is either the before or after offset.
     *
     * @param offset  the offset to check, null returns false
     * @return true if the offset is valid during the transition
     */
    public boolean isValidOffset(ZoneOffset offset) {
        return isGap() ? false : (getOffsetBefore().equals(offset) || getOffsetAfter().equals(offset));
    }

    
Gets the valid offsets during this transition.


A gap will return an empty list, while an overlap will return both offsets.

Returns:the list of valid offsets
/**
     * Gets the valid offsets during this transition.
     * <p>
     * A gap will return an empty list, while an overlap will return both offsets.
     *
     * @return the list of valid offsets
     */
    List<ZoneOffset> getValidOffsets() {
        if (isGap()) {
            return List.of();
        }
        return List.of(getOffsetBefore(), getOffsetAfter());
    }

    //-----------------------------------------------------------------------
    
Compares this transition to another based on the transition instant.


This compares the instants of each transition.
The offsets are ignored, making this order inconsistent with equals.

Params:
  • transition –  the transition to compare to, not null
Returns:the comparator value, negative if less, positive if greater
/**
     * Compares this transition to another based on the transition instant.
     * <p>
     * This compares the instants of each transition.
     * The offsets are ignored, making this order inconsistent with equals.
     *
     * @param transition  the transition to compare to, not null
     * @return the comparator value, negative if less, positive if greater
     */
    @Override
    public int compareTo(ZoneOffsetTransition transition) {
        return Long.compare(epochSecond, transition.epochSecond);
    }

    //-----------------------------------------------------------------------
    
Checks if this object equals another.


The entire state of the object is compared.

Params:
  • other –  the other object to compare to, null returns false
Returns:true if equal
/**
     * Checks if this object equals another.
     * <p>
     * The entire state of the object is compared.
     *
     * @param other  the other object to compare to, null returns false
     * @return true if equal
     */
    @Override
    public boolean equals(Object other) {
        if (other == this) {
            return true;
        }
        if (other instanceof ZoneOffsetTransition) {
            ZoneOffsetTransition d = (ZoneOffsetTransition) other;
            return epochSecond == d.epochSecond &&
                offsetBefore.equals(d.offsetBefore) && offsetAfter.equals(d.offsetAfter);
        }
        return false;
    }

    
Returns a suitable hash code.

Returns:the hash code
/**
     * Returns a suitable hash code.
     *
     * @return the hash code
     */
    @Override
    public int hashCode() {
        return transition.hashCode() ^ offsetBefore.hashCode() ^ Integer.rotateLeft(offsetAfter.hashCode(), 16);
    }

    //-----------------------------------------------------------------------
    
Returns a string describing this object.

Returns:a string for debugging, not null
/**
     * Returns a string describing this object.
     *
     * @return a string for debugging, not null
     */
    @Override
    public String toString() {
        StringBuilder buf = new StringBuilder();
        buf.append("Transition[")
            .append(isGap() ? "Gap" : "Overlap")
            .append(" at ")
            .append(transition)
            .append(offsetBefore)
            .append(" to ")
            .append(offsetAfter)
            .append(']');
        return buf.toString();
    }

}