1 /*
2 * Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 /*
27 * This file is available under and governed by the GNU General Public
28 * License version 2 only, as published by the Free Software Foundation.
29 * However, the following notice accompanied the original version of this
30 * file:
31 *
32 * Copyright (c) 2009-2012, Stephen Colebourne & Michael Nascimento Santos
33 *
34 * All rights reserved.
35 *
36 * Redistribution and use in source and binary forms, with or without
37 * modification, are permitted provided that the following conditions are met:
38 *
39 * * Redistributions of source code must retain the above copyright notice,
40 * this list of conditions and the following disclaimer.
41 *
42 * * Redistributions in binary form must reproduce the above copyright notice,
43 * this list of conditions and the following disclaimer in the documentation
44 * and/or other materials provided with the distribution.
45 *
46 * * Neither the name of JSR-310 nor the names of its contributors
47 * may be used to endorse or promote products derived from this software
48 * without specific prior written permission.
49 *
50 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
51 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
52 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
53 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
54 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
55 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
56 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
57 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
58 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
59 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
60 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
61 */
62 package java.time.zone;
63
64 import java.io.DataInput;
65 import java.io.DataOutput;
66 import java.io.IOException;
67 import java.io.Serializable;
68 import java.time.Duration;
69 import java.time.Instant;
70 import java.time.LocalDateTime;
71 import java.time.ZoneOffset;
72 import java.util.Arrays;
73 import java.util.Collections;
74 import java.util.List;
75 import java.util.Objects;
76
77 /**
78 * A transition between two offsets caused by a discontinuity in the local time-line.
79 * <p>
80 * A transition between two offsets is normally the result of a daylight savings cutover.
81 * The discontinuity is normally a gap in spring and an overlap in autumn.
82 * {@code ZoneOffsetTransition} models the transition between the two offsets.
83 * <p>
84 * Gaps occur where there are local date-times that simply do not not exist.
85 * An example would be when the offset changes from {@code +03:00} to {@code +04:00}.
86 * This might be described as 'the clocks will move forward one hour tonight at 1am'.
87 * <p>
88 * Overlaps occur where there are local date-times that exist twice.
89 * An example would be when the offset changes from {@code +04:00} to {@code +03:00}.
90 * This might be described as 'the clocks will move back one hour tonight at 2am'.
91 *
92 * <h3>Specification for implementors</h3>
93 * This class is immutable and thread-safe.
94 *
95 * @since 1.8
96 */
97 public final class ZoneOffsetTransition
98 implements Comparable<ZoneOffsetTransition>, Serializable {
99
100 /**
101 * Serialization version.
102 */
103 private static final long serialVersionUID = -6946044323557704546L;
104 /**
105 * The local transition date-time at the transition.
106 */
107 private final LocalDateTime transition;
108 /**
109 * The offset before transition.
110 */
111 private final ZoneOffset offsetBefore;
112 /**
113 * The offset after transition.
114 */
115 private final ZoneOffset offsetAfter;
116
117 //-----------------------------------------------------------------------
118 /**
119 * Obtains an instance defining a transition between two offsets.
120 * <p>
121 * Applications should normally obtain an instance from {@link ZoneRules}.
122 * This factory is only intended for use when creating {@link ZoneRules}.
123 *
124 * @param transition the transition date-time at the transition, which never
125 * actually occurs, expressed local to the before offset, not null
126 * @param offsetBefore the offset before the transition, not null
127 * @param offsetAfter the offset at and after the transition, not null
128 * @return the transition, not null
129 * @throws IllegalArgumentException if {@code offsetBefore} and {@code offsetAfter}
130 * are equal, or {@code transition.getNano()} returns non-zero value
131 */
132 public static ZoneOffsetTransition of(LocalDateTime transition, ZoneOffset offsetBefore, ZoneOffset offsetAfter) {
133 Objects.requireNonNull(transition, "transition");
134 Objects.requireNonNull(offsetBefore, "offsetBefore");
135 Objects.requireNonNull(offsetAfter, "offsetAfter");
136 if (offsetBefore.equals(offsetAfter)) {
137 throw new IllegalArgumentException("Offsets must not be equal");
138 }
139 if (transition.getNano() != 0) {
140 throw new IllegalArgumentException("Nano-of-second must be zero");
141 }
142 return new ZoneOffsetTransition(transition, offsetBefore, offsetAfter);
143 }
144
145 /**
146 * Creates an instance defining a transition between two offsets.
147 *
148 * @param transition the transition date-time with the offset before the transition, not null
149 * @param offsetBefore the offset before the transition, not null
150 * @param offsetAfter the offset at and after the transition, not null
151 */
152 ZoneOffsetTransition(LocalDateTime transition, ZoneOffset offsetBefore, ZoneOffset offsetAfter) {
153 this.transition = transition;
154 this.offsetBefore = offsetBefore;
155 this.offsetAfter = offsetAfter;
156 }
157
158 /**
159 * Creates an instance from epoch-second and offsets.
160 *
161 * @param epochSecond the transition epoch-second
162 * @param offsetBefore the offset before the transition, not null
163 * @param offsetAfter the offset at and after the transition, not null
164 */
165 ZoneOffsetTransition(long epochSecond, ZoneOffset offsetBefore, ZoneOffset offsetAfter) {
166 this.transition = LocalDateTime.ofEpochSecond(epochSecond, 0, offsetBefore);
167 this.offsetBefore = offsetBefore;
168 this.offsetAfter = offsetAfter;
169 }
170
171 //-----------------------------------------------------------------------
172 /**
173 * Uses a serialization delegate.
174 *
175 * @return the replacing object, not null
176 */
177 private Object writeReplace() {
178 return new Ser(Ser.ZOT, this);
179 }
180
181 /**
182 * Writes the state to the stream.
183 *
184 * @param out the output stream, not null
185 * @throws IOException if an error occurs
186 */
187 void writeExternal(DataOutput out) throws IOException {
188 Ser.writeEpochSec(toEpochSecond(), out);
189 Ser.writeOffset(offsetBefore, out);
190 Ser.writeOffset(offsetAfter, out);
191 }
192
193 /**
194 * Reads the state from the stream.
195 *
196 * @param in the input stream, not null
197 * @return the created object, not null
198 * @throws IOException if an error occurs
199 */
200 static ZoneOffsetTransition readExternal(DataInput in) throws IOException {
201 long epochSecond = Ser.readEpochSec(in);
202 ZoneOffset before = Ser.readOffset(in);
203 ZoneOffset after = Ser.readOffset(in);
204 if (before.equals(after)) {
205 throw new IllegalArgumentException("Offsets must not be equal");
206 }
207 return new ZoneOffsetTransition(epochSecond, before, after);
208 }
209
210 //-----------------------------------------------------------------------
211 /**
212 * Gets the transition instant.
213 * <p>
214 * This is the instant of the discontinuity, which is defined as the first
215 * instant that the 'after' offset applies.
216 * <p>
217 * The methods {@link #getInstant()}, {@link #getDateTimeBefore()} and {@link #getDateTimeAfter()}
218 * all represent the same instant.
219 *
220 * @return the transition instant, not null
221 */
222 public Instant getInstant() {
223 return transition.toInstant(offsetBefore);
224 }
225
226 /**
227 * Gets the transition instant as an epoch second.
228 *
229 * @return the transition epoch second
230 */
231 public long toEpochSecond() {
232 return transition.toEpochSecond(offsetBefore);
233 }
234
235 //-------------------------------------------------------------------------
236 /**
237 * Gets the local transition date-time, as would be expressed with the 'before' offset.
238 * <p>
239 * This is the date-time where the discontinuity begins expressed with the 'before' offset.
240 * At this instant, the 'after' offset is actually used, therefore the combination of this
241 * date-time and the 'before' offset will never occur.
242 * <p>
243 * The combination of the 'before' date-time and offset represents the same instant
244 * as the 'after' date-time and offset.
245 *
246 * @return the transition date-time expressed with the before offset, not null
247 */
248 public LocalDateTime getDateTimeBefore() {
249 return transition;
250 }
251
252 /**
253 * Gets the local transition date-time, as would be expressed with the 'after' offset.
254 * <p>
255 * This is the first date-time after the discontinuity, when the new offset applies.
256 * <p>
257 * The combination of the 'before' date-time and offset represents the same instant
258 * as the 'after' date-time and offset.
259 *
260 * @return the transition date-time expressed with the after offset, not null
261 */
262 public LocalDateTime getDateTimeAfter() {
263 return transition.plusSeconds(getDurationSeconds());
264 }
265
266 /**
267 * Gets the offset before the transition.
268 * <p>
269 * This is the offset in use before the instant of the transition.
270 *
271 * @return the offset before the transition, not null
272 */
273 public ZoneOffset getOffsetBefore() {
274 return offsetBefore;
275 }
276
277 /**
278 * Gets the offset after the transition.
279 * <p>
280 * This is the offset in use on and after the instant of the transition.
281 *
282 * @return the offset after the transition, not null
283 */
284 public ZoneOffset getOffsetAfter() {
285 return offsetAfter;
286 }
287
288 /**
289 * Gets the duration of the transition.
290 * <p>
291 * In most cases, the transition duration is one hour, however this is not always the case.
292 * The duration will be positive for a gap and negative for an overlap.
293 * Time-zones are second-based, so the nanosecond part of the duration will be zero.
294 *
295 * @return the duration of the transition, positive for gaps, negative for overlaps
296 */
297 public Duration getDuration() {
298 return Duration.ofSeconds(getDurationSeconds());
299 }
300
301 /**
302 * Gets the duration of the transition in seconds.
303 *
304 * @return the duration in seconds
305 */
306 private int getDurationSeconds() {
307 return getOffsetAfter().getTotalSeconds() - getOffsetBefore().getTotalSeconds();
308 }
309
310 /**
311 * Does this transition represent a gap in the local time-line.
312 * <p>
313 * Gaps occur where there are local date-times that simply do not not exist.
314 * An example would be when the offset changes from {@code +01:00} to {@code +02:00}.
315 * This might be described as 'the clocks will move forward one hour tonight at 1am'.
316 *
317 * @return true if this transition is a gap, false if it is an overlap
318 */
319 public boolean isGap() {
320 return getOffsetAfter().getTotalSeconds() > getOffsetBefore().getTotalSeconds();
321 }
322
323 /**
324 * Does this transition represent a gap in the local time-line.
325 * <p>
326 * Overlaps occur where there are local date-times that exist twice.
327 * An example would be when the offset changes from {@code +02:00} to {@code +01:00}.
328 * This might be described as 'the clocks will move back one hour tonight at 2am'.
329 *
330 * @return true if this transition is an overlap, false if it is a gap
331 */
332 public boolean isOverlap() {
333 return getOffsetAfter().getTotalSeconds() < getOffsetBefore().getTotalSeconds();
334 }
335
336 /**
337 * Checks if the specified offset is valid during this transition.
338 * <p>
339 * This checks to see if the given offset will be valid at some point in the transition.
340 * A gap will always return false.
341 * An overlap will return true if the offset is either the before or after offset.
342 *
343 * @param offset the offset to check, null returns false
344 * @return true if the offset is valid during the transition
345 */
346 public boolean isValidOffset(ZoneOffset offset) {
347 return isGap() ? false : (getOffsetBefore().equals(offset) || getOffsetAfter().equals(offset));
348 }
349
350 /**
351 * Gets the valid offsets during this transition.
352 * <p>
353 * A gap will return an empty list, while an overlap will return both offsets.
354 *
355 * @return the list of valid offsets
356 */
357 List<ZoneOffset> getValidOffsets() {
358 if (isGap()) {
359 return Collections.emptyList();
360 }
361 return Arrays.asList(getOffsetBefore(), getOffsetAfter());
362 }
363
364 //-----------------------------------------------------------------------
365 /**
366 * Compares this transition to another based on the transition instant.
367 * <p>
368 * This compares the instants of each transition.
369 * The offsets are ignored, making this order inconsistent with equals.
370 *
371 * @param transition the transition to compare to, not null
372 * @return the comparator value, negative if less, positive if greater
373 */
374 @Override
375 public int compareTo(ZoneOffsetTransition transition) {
376 return this.getInstant().compareTo(transition.getInstant());
377 }
378
379 //-----------------------------------------------------------------------
380 /**
381 * Checks if this object equals another.
382 * <p>
383 * The entire state of the object is compared.
384 *
385 * @param other the other object to compare to, null returns false
386 * @return true if equal
387 */
388 @Override
389 public boolean equals(Object other) {
390 if (other == this) {
391 return true;
392 }
393 if (other instanceof ZoneOffsetTransition) {
394 ZoneOffsetTransition d = (ZoneOffsetTransition) other;
395 return transition.equals(d.transition) &&
396 offsetBefore.equals(d.offsetBefore) && offsetAfter.equals(d.offsetAfter);
397 }
398 return false;
399 }
400
401 /**
402 * Returns a suitable hash code.
403 *
404 * @return the hash code
405 */
406 @Override
407 public int hashCode() {
408 return transition.hashCode() ^ offsetBefore.hashCode() ^ Integer.rotateLeft(offsetAfter.hashCode(), 16);
409 }
410
411 //-----------------------------------------------------------------------
412 /**
413 * Returns a string describing this object.
414 *
415 * @return a string for debugging, not null
416 */
417 @Override
418 public String toString() {
419 StringBuilder buf = new StringBuilder();
420 buf.append("Transition[")
421 .append(isGap() ? "Gap" : "Overlap")
422 .append(" at ")
423 .append(transition)
424 .append(offsetBefore)
425 .append(" to ")
426 .append(offsetAfter)
427 .append(']');
428 return buf.toString();
429 }
430
431 }