| 1 | /* |
| 2 | * Copyright 2001-2005 Stephen Colebourne |
| 3 | * |
| 4 | * Licensed under the Apache License, Version 2.0 (the "License"); |
| 5 | * you may not use this file except in compliance with the License. |
| 6 | * You may obtain a copy of the License at |
| 7 | * |
| 8 | * http://www.apache.org/licenses/LICENSE-2.0 |
| 9 | * |
| 10 | * Unless required by applicable law or agreed to in writing, software |
| 11 | * distributed under the License is distributed on an "AS IS" BASIS, |
| 12 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 13 | * See the License for the specific language governing permissions and |
| 14 | * limitations under the License. |
| 15 | */ |
| 16 | package org.joda.time.chrono; |
| 17 | |
| 18 | import java.io.Serializable; |
| 19 | import java.util.HashMap; |
| 20 | import java.util.Map; |
| 21 | |
| 22 | import org.joda.time.Chronology; |
| 23 | import org.joda.time.DateTime; |
| 24 | import org.joda.time.DateTimeConstants; |
| 25 | import org.joda.time.DateTimeField; |
| 26 | import org.joda.time.DateTimeZone; |
| 27 | |
| 28 | /** |
| 29 | * Implements the Islamic, or Hijri, calendar system using arithmetic rules. |
| 30 | * <p> |
| 31 | * This calendar is a lunar calendar with a shorter year than ISO. |
| 32 | * Year 1 in the Islamic calendar began on July 16, 622 CE (Julian), thus |
| 33 | * Islamic years do not begin at the same time as Julian years. This chronology |
| 34 | * is not proleptic, as it does not allow dates before the first Islamic year. |
| 35 | * <p> |
| 36 | * There are two basic forms of the Islamic calendar, the tabular and the |
| 37 | * observed. The observed form cannot easily be used by computers as it |
| 38 | * relies on human observation of the new moon. |
| 39 | * The tabular calendar, implemented here, is an arithmetical approximation |
| 40 | * of the observed form that follows relatively simple rules. |
| 41 | * <p> |
| 42 | * The tabular form of the calendar defines 12 months of alternately |
| 43 | * 30 and 29 days. The last month is extended to 30 days in a leap year. |
| 44 | * Leap years occur according to a 30 year cycle. There are four recognised |
| 45 | * patterns of leap years in the 30 year cycle: |
| 46 | * <pre> |
| 47 | * Years 2, 5, 7, 10, 13, 15, 18, 21, 24, 26 & 29 - 15-based, used by Microsoft |
| 48 | * Years 2, 5, 7, 10, 13, 16, 18, 21, 24, 26 & 29 - 16-based, most commonly used |
| 49 | * Years 2, 5, 8, 10, 13, 16, 19, 21, 24, 27 & 29 - Indian |
| 50 | * Years 2, 5, 8, 11, 13, 16, 19, 21, 24, 27 & 30 - Habash al-Hasib |
| 51 | * </pre> |
| 52 | * You can select which pattern to use via the factory methods, or use the |
| 53 | * default (16-based). |
| 54 | * <p> |
| 55 | * This implementation defines a day as midnight to midnight exactly as per |
| 56 | * the ISO chronology. This correct start of day is at sunset on the previous |
| 57 | * day, however this cannot readily be modelled and has been ignored. |
| 58 | * <p> |
| 59 | * IslamicChronology is thread-safe and immutable. |
| 60 | * |
| 61 | * @see <a href="http://en.wikipedia.org/wiki/Islamic_calendar">Wikipedia</a> |
| 62 | * |
| 63 | * @author Stephen Colebourne |
| 64 | * @since 1.2 |
| 65 | */ |
| 66 | public final class IslamicChronology extends BasicChronology { |
| 67 | |
| 68 | /** Serialization lock */ |
| 69 | private static final long serialVersionUID = -3663823829888L; |
| 70 | |
| 71 | /** |
| 72 | * Constant value for 'Anno Hegirae', equivalent |
| 73 | * to the value returned for AD/CE. |
| 74 | */ |
| 75 | public static final int AH = DateTimeConstants.CE; |
| 76 | |
| 77 | /** A singleton era field. */ |
| 78 | private static final DateTimeField ERA_FIELD = new BasicSingleEraDateTimeField("AH"); |
| 79 | |
| 80 | /** Leap year 15-based pattern. */ |
| 81 | public static final LeapYearPatternType LEAP_YEAR_15_BASED = new LeapYearPatternType(0, 623158436); |
| 82 | /** Leap year 16-based pattern. */ |
| 83 | public static final LeapYearPatternType LEAP_YEAR_16_BASED = new LeapYearPatternType(1, 623191204); |
| 84 | /** Leap year Indian pattern. */ |
| 85 | public static final LeapYearPatternType LEAP_YEAR_INDIAN = new LeapYearPatternType(2, 690562340); |
| 86 | /** Leap year Habash al-Hasib pattern. */ |
| 87 | public static final LeapYearPatternType LEAP_YEAR_HABASH_AL_HASIB = new LeapYearPatternType(3, 153692453); |
| 88 | |
| 89 | /** The lowest year that can be fully supported. */ |
| 90 | private static final int MIN_YEAR = -292269337; |
| 91 | |
| 92 | /** |
| 93 | * The highest year that can be fully supported. |
| 94 | * Although calculateFirstDayOfYearMillis can go higher without |
| 95 | * overflowing, the getYear method overflows when it adds the |
| 96 | * approximate millis at the epoch. |
| 97 | */ |
| 98 | private static final int MAX_YEAR = 292271022; |
| 99 | |
| 100 | /** The days in a pair of months. */ |
| 101 | private static final int MONTH_PAIR_LENGTH = 59; |
| 102 | |
| 103 | /** The length of the long month. */ |
| 104 | private static final int LONG_MONTH_LENGTH = 30; |
| 105 | |
| 106 | /** The length of the short month. */ |
| 107 | private static final int SHORT_MONTH_LENGTH = 29; |
| 108 | |
| 109 | /** The length of the long month in millis. */ |
| 110 | private static final long MILLIS_PER_MONTH_PAIR = 59L * DateTimeConstants.MILLIS_PER_DAY; |
| 111 | |
| 112 | /** The length of the long month in millis. */ |
| 113 | private static final long MILLIS_PER_MONTH = (long) (29.53056 * DateTimeConstants.MILLIS_PER_DAY); |
| 114 | |
| 115 | /** The length of the long month in millis. */ |
| 116 | private static final long MILLIS_PER_LONG_MONTH = 30L * DateTimeConstants.MILLIS_PER_DAY; |
| 117 | |
| 118 | /** The typical millis per year. */ |
| 119 | private static final long MILLIS_PER_YEAR = (long) (354.36667 * DateTimeConstants.MILLIS_PER_DAY); |
| 120 | |
| 121 | /** The typical millis per year. */ |
| 122 | private static final long MILLIS_PER_SHORT_YEAR = 354L * DateTimeConstants.MILLIS_PER_DAY; |
| 123 | |
| 124 | /** The typical millis per year. */ |
| 125 | private static final long MILLIS_PER_LONG_YEAR = 355L * DateTimeConstants.MILLIS_PER_DAY; |
| 126 | |
| 127 | /** The millis of 0001-01-01. */ |
| 128 | private static final long MILLIS_YEAR_1 = -42521587200000L; |
| 129 | // -42520809600000L; |
| 130 | // long start = 0L - 278L * DateTimeConstants.MILLIS_PER_DAY; |
| 131 | // long cy = 46L * MILLIS_PER_CYCLE; // 1381-01-01 |
| 132 | // long rem = 5L * MILLIS_PER_SHORT_YEAR + |
| 133 | // 3L * MILLIS_PER_LONG_YEAR; // 1389-01-01 |
| 134 | |
| 135 | /** The length of the cycle of leap years. */ |
| 136 | private static final int CYCLE = 30; |
| 137 | |
| 138 | /** The millis of a 30 year cycle. */ |
| 139 | private static final long MILLIS_PER_CYCLE = ((19L * 354L + 11L * 355L) * DateTimeConstants.MILLIS_PER_DAY); |
| 140 | |
| 141 | /** Cache of zone to chronology arrays */ |
| 142 | private static final Map cCache = new HashMap(); |
| 143 | |
| 144 | /** Singleton instance of a UTC IslamicChronology */ |
| 145 | private static final IslamicChronology INSTANCE_UTC; |
| 146 | static { |
| 147 | // init after static fields |
| 148 | INSTANCE_UTC = getInstance(DateTimeZone.UTC); |
| 149 | } |
| 150 | |
| 151 | /** The leap years to use. */ |
| 152 | private final LeapYearPatternType iLeapYears; |
| 153 | |
| 154 | //----------------------------------------------------------------------- |
| 155 | /** |
| 156 | * Gets an instance of the IslamicChronology. |
| 157 | * The time zone of the returned instance is UTC. |
| 158 | * |
| 159 | * @return a singleton UTC instance of the chronology |
| 160 | */ |
| 161 | public static IslamicChronology getInstanceUTC() { |
| 162 | return INSTANCE_UTC; |
| 163 | } |
| 164 | |
| 165 | /** |
| 166 | * Gets an instance of the IslamicChronology in the default time zone. |
| 167 | * |
| 168 | * @return a chronology in the default time zone |
| 169 | */ |
| 170 | public static IslamicChronology getInstance() { |
| 171 | return getInstance(DateTimeZone.getDefault(), LEAP_YEAR_16_BASED); |
| 172 | } |
| 173 | |
| 174 | /** |
| 175 | * Gets an instance of the IslamicChronology in the given time zone. |
| 176 | * |
| 177 | * @param zone the time zone to get the chronology in, null is default |
| 178 | * @return a chronology in the specified time zone |
| 179 | */ |
| 180 | public static IslamicChronology getInstance(DateTimeZone zone) { |
| 181 | return getInstance(zone, LEAP_YEAR_16_BASED); |
| 182 | } |
| 183 | |
| 184 | /** |
| 185 | * Gets an instance of the IslamicChronology in the given time zone. |
| 186 | * |
| 187 | * @param zone the time zone to get the chronology in, null is default |
| 188 | * @param leapYears the type defining the leap year pattern |
| 189 | * @return a chronology in the specified time zone |
| 190 | */ |
| 191 | public static IslamicChronology getInstance(DateTimeZone zone, LeapYearPatternType leapYears) { |
| 192 | if (zone == null) { |
| 193 | zone = DateTimeZone.getDefault(); |
| 194 | } |
| 195 | IslamicChronology chrono; |
| 196 | synchronized (cCache) { |
| 197 | IslamicChronology[] chronos = (IslamicChronology[]) cCache.get(zone); |
| 198 | if (chronos == null) { |
| 199 | chronos = new IslamicChronology[4]; |
| 200 | cCache.put(zone, chronos); |
| 201 | } |
| 202 | chrono = chronos[leapYears.index]; |
| 203 | if (chrono == null) { |
| 204 | if (zone == DateTimeZone.UTC) { |
| 205 | // First create without a lower limit. |
| 206 | chrono = new IslamicChronology(null, null, leapYears); |
| 207 | // Impose lower limit and make another IslamicChronology. |
| 208 | DateTime lowerLimit = new DateTime(1, 1, 1, 0, 0, 0, 0, chrono); |
| 209 | chrono = new IslamicChronology( |
| 210 | LimitChronology.getInstance(chrono, lowerLimit, null), |
| 211 | null, leapYears); |
| 212 | } else { |
| 213 | chrono = getInstance(DateTimeZone.UTC, leapYears); |
| 214 | chrono = new IslamicChronology |
| 215 | (ZonedChronology.getInstance(chrono, zone), null, leapYears); |
| 216 | } |
| 217 | chronos[leapYears.index] = chrono; |
| 218 | } |
| 219 | } |
| 220 | return chrono; |
| 221 | } |
| 222 | |
| 223 | // Constructors and instance variables |
| 224 | //----------------------------------------------------------------------- |
| 225 | /** |
| 226 | * Restricted constructor. |
| 227 | */ |
| 228 | IslamicChronology(Chronology base, Object param, LeapYearPatternType leapYears) { |
| 229 | super(base, param, 4); |
| 230 | this.iLeapYears = leapYears; |
| 231 | } |
| 232 | |
| 233 | /** |
| 234 | * Serialization singleton. |
| 235 | */ |
| 236 | private Object readResolve() { |
| 237 | Chronology base = getBase(); |
| 238 | return base == null ? getInstanceUTC() : getInstance(base.getZone()); |
| 239 | } |
| 240 | |
| 241 | //----------------------------------------------------------------------- |
| 242 | /** |
| 243 | * Gets the leap year pattern type. |
| 244 | * |
| 245 | * @return the pattern type |
| 246 | */ |
| 247 | public LeapYearPatternType getLeapYearPatternType() { |
| 248 | return iLeapYears; |
| 249 | } |
| 250 | |
| 251 | // Conversion |
| 252 | //----------------------------------------------------------------------- |
| 253 | /** |
| 254 | * Gets the Chronology in the UTC time zone. |
| 255 | * |
| 256 | * @return the chronology in UTC |
| 257 | */ |
| 258 | public Chronology withUTC() { |
| 259 | return INSTANCE_UTC; |
| 260 | } |
| 261 | |
| 262 | /** |
| 263 | * Gets the Chronology in a specific time zone. |
| 264 | * |
| 265 | * @param zone the zone to get the chronology in, null is default |
| 266 | * @return the chronology |
| 267 | */ |
| 268 | public Chronology withZone(DateTimeZone zone) { |
| 269 | if (zone == null) { |
| 270 | zone = DateTimeZone.getDefault(); |
| 271 | } |
| 272 | if (zone == getZone()) { |
| 273 | return this; |
| 274 | } |
| 275 | return getInstance(zone); |
| 276 | } |
| 277 | |
| 278 | /** |
| 279 | * A suitable hash code for the chronology. |
| 280 | * |
| 281 | * @return the hash code |
| 282 | * @since 1.6 |
| 283 | */ |
| 284 | public int hashCode() { |
| 285 | return super.hashCode() * 13 + getLeapYearPatternType().hashCode(); |
| 286 | } |
| 287 | |
| 288 | //----------------------------------------------------------------------- |
| 289 | int getYear(long instant) { |
| 290 | long millisIslamic = instant - MILLIS_YEAR_1; |
| 291 | long cycles = millisIslamic / MILLIS_PER_CYCLE; |
| 292 | long cycleRemainder = millisIslamic % MILLIS_PER_CYCLE; |
| 293 | |
| 294 | int year = (int) ((cycles * CYCLE) + 1L); |
| 295 | long yearMillis = (isLeapYear(year) ? MILLIS_PER_LONG_YEAR : MILLIS_PER_SHORT_YEAR); |
| 296 | while (cycleRemainder >= yearMillis) { |
| 297 | cycleRemainder -= yearMillis; |
| 298 | yearMillis = (isLeapYear(++year) ? MILLIS_PER_LONG_YEAR : MILLIS_PER_SHORT_YEAR); |
| 299 | } |
| 300 | return year; |
| 301 | } |
| 302 | |
| 303 | long setYear(long instant, int year) { |
| 304 | // optimsed implementation of set, due to fixed months |
| 305 | int thisYear = getYear(instant); |
| 306 | int dayOfYear = getDayOfYear(instant, thisYear); |
| 307 | int millisOfDay = getMillisOfDay(instant); |
| 308 | |
| 309 | if (dayOfYear > 354) { |
| 310 | // Current year is leap, and day is leap. |
| 311 | if (!isLeapYear(year)) { |
| 312 | // Moving to a non-leap year, leap day doesn't exist. |
| 313 | dayOfYear--; |
| 314 | } |
| 315 | } |
| 316 | |
| 317 | instant = getYearMonthDayMillis(year, 1, dayOfYear); |
| 318 | instant += millisOfDay; |
| 319 | return instant; |
| 320 | } |
| 321 | |
| 322 | //----------------------------------------------------------------------- |
| 323 | long getYearDifference(long minuendInstant, long subtrahendInstant) { |
| 324 | // optimsed implementation of getDifference, due to fixed months |
| 325 | int minuendYear = getYear(minuendInstant); |
| 326 | int subtrahendYear = getYear(subtrahendInstant); |
| 327 | |
| 328 | // Inlined remainder method to avoid duplicate calls to get. |
| 329 | long minuendRem = minuendInstant - getYearMillis(minuendYear); |
| 330 | long subtrahendRem = subtrahendInstant - getYearMillis(subtrahendYear); |
| 331 | |
| 332 | int difference = minuendYear - subtrahendYear; |
| 333 | if (minuendRem < subtrahendRem) { |
| 334 | difference--; |
| 335 | } |
| 336 | return difference; |
| 337 | } |
| 338 | |
| 339 | //----------------------------------------------------------------------- |
| 340 | long getTotalMillisByYearMonth(int year, int month) { |
| 341 | if (--month % 2 == 1) { |
| 342 | month /= 2; |
| 343 | return month * MILLIS_PER_MONTH_PAIR + MILLIS_PER_LONG_MONTH; |
| 344 | } else { |
| 345 | month /= 2; |
| 346 | return month * MILLIS_PER_MONTH_PAIR; |
| 347 | } |
| 348 | } |
| 349 | |
| 350 | //----------------------------------------------------------------------- |
| 351 | int getDayOfMonth(long millis) { |
| 352 | // optimised for simple months |
| 353 | int doy = getDayOfYear(millis) - 1; |
| 354 | if (doy == 354) { |
| 355 | return 30; |
| 356 | } |
| 357 | return (doy % MONTH_PAIR_LENGTH) % LONG_MONTH_LENGTH + 1; |
| 358 | } |
| 359 | |
| 360 | //----------------------------------------------------------------------- |
| 361 | boolean isLeapYear(int year) { |
| 362 | return iLeapYears.isLeapYear(year); |
| 363 | } |
| 364 | |
| 365 | //----------------------------------------------------------------------- |
| 366 | int getDaysInYearMax() { |
| 367 | return 355; |
| 368 | } |
| 369 | |
| 370 | //----------------------------------------------------------------------- |
| 371 | int getDaysInYear(int year) { |
| 372 | return isLeapYear(year) ? 355 : 354; |
| 373 | } |
| 374 | |
| 375 | //----------------------------------------------------------------------- |
| 376 | int getDaysInYearMonth(int year, int month) { |
| 377 | if (month == 12 && isLeapYear(year)) { |
| 378 | return LONG_MONTH_LENGTH; |
| 379 | } |
| 380 | return (--month % 2 == 0 ? LONG_MONTH_LENGTH : SHORT_MONTH_LENGTH); |
| 381 | } |
| 382 | |
| 383 | //----------------------------------------------------------------------- |
| 384 | int getDaysInMonthMax() { |
| 385 | return LONG_MONTH_LENGTH; |
| 386 | } |
| 387 | |
| 388 | //----------------------------------------------------------------------- |
| 389 | int getDaysInMonthMax(int month) { |
| 390 | if (month == 12) { |
| 391 | return LONG_MONTH_LENGTH; |
| 392 | } |
| 393 | return (--month % 2 == 0 ? LONG_MONTH_LENGTH : SHORT_MONTH_LENGTH); |
| 394 | } |
| 395 | |
| 396 | //----------------------------------------------------------------------- |
| 397 | int getMonthOfYear(long millis, int year) { |
| 398 | int doyZeroBased = (int) ((millis - getYearMillis(year)) / DateTimeConstants.MILLIS_PER_DAY); |
| 399 | if (doyZeroBased == 354) { |
| 400 | return 12; |
| 401 | } |
| 402 | return ((doyZeroBased * 2) / MONTH_PAIR_LENGTH) + 1; |
| 403 | // return (int) (doyZeroBased / 29.9f) + 1; |
| 404 | // |
| 405 | // int monthPairZeroBased = doyZeroBased / MONTH_PAIR_LENGTH; |
| 406 | // int monthPairRemainder = doyZeroBased % MONTH_PAIR_LENGTH; |
| 407 | // return (monthPairZeroBased * 2) + 1 + (monthPairRemainder >= LONG_MONTH_LENGTH ? 1 : 0); |
| 408 | } |
| 409 | |
| 410 | //----------------------------------------------------------------------- |
| 411 | long getAverageMillisPerYear() { |
| 412 | return MILLIS_PER_YEAR; |
| 413 | } |
| 414 | |
| 415 | //----------------------------------------------------------------------- |
| 416 | long getAverageMillisPerYearDividedByTwo() { |
| 417 | return MILLIS_PER_YEAR / 2; |
| 418 | } |
| 419 | |
| 420 | //----------------------------------------------------------------------- |
| 421 | long getAverageMillisPerMonth() { |
| 422 | return MILLIS_PER_MONTH; |
| 423 | } |
| 424 | |
| 425 | //----------------------------------------------------------------------- |
| 426 | long calculateFirstDayOfYearMillis(int year) { |
| 427 | if (year > MAX_YEAR) { |
| 428 | throw new ArithmeticException("Year is too large: " + year + " > " + MAX_YEAR); |
| 429 | } |
| 430 | if (year < MIN_YEAR) { |
| 431 | throw new ArithmeticException("Year is too small: " + year + " < " + MIN_YEAR); |
| 432 | } |
| 433 | |
| 434 | // Java epoch is 1970-01-01 Gregorian which is 0622-07-16 Islamic. |
| 435 | // 0001-01-01 Islamic is -42520809600000L |
| 436 | // would prefer to calculate against year zero, but leap year |
| 437 | // can be in that year so it doesn't work |
| 438 | year--; |
| 439 | long cycle = year / CYCLE; |
| 440 | long millis = MILLIS_YEAR_1 + cycle * MILLIS_PER_CYCLE; |
| 441 | int cycleRemainder = (year % CYCLE) + 1; |
| 442 | |
| 443 | for (int i = 1; i < cycleRemainder; i++) { |
| 444 | millis += (isLeapYear(i) ? MILLIS_PER_LONG_YEAR : MILLIS_PER_SHORT_YEAR); |
| 445 | } |
| 446 | |
| 447 | return millis; |
| 448 | } |
| 449 | |
| 450 | //----------------------------------------------------------------------- |
| 451 | int getMinYear() { |
| 452 | return 1; //MIN_YEAR; |
| 453 | } |
| 454 | |
| 455 | //----------------------------------------------------------------------- |
| 456 | int getMaxYear() { |
| 457 | return MAX_YEAR; |
| 458 | } |
| 459 | |
| 460 | //----------------------------------------------------------------------- |
| 461 | long getApproxMillisAtEpochDividedByTwo() { |
| 462 | // Epoch 1970-01-01 ISO = 1389-10-22 Islamic |
| 463 | return (-MILLIS_YEAR_1) / 2; |
| 464 | } |
| 465 | |
| 466 | //----------------------------------------------------------------------- |
| 467 | protected void assemble(Fields fields) { |
| 468 | if (getBase() == null) { |
| 469 | super.assemble(fields); |
| 470 | |
| 471 | fields.era = ERA_FIELD; |
| 472 | fields.monthOfYear = new BasicMonthOfYearDateTimeField(this, 12); |
| 473 | fields.months = fields.monthOfYear.getDurationField(); |
| 474 | } |
| 475 | } |
| 476 | |
| 477 | //----------------------------------------------------------------------- |
| 478 | /** |
| 479 | * Opaque object describing a leap year pattern for the Islamic Chronology. |
| 480 | * |
| 481 | * @since 1.2 |
| 482 | */ |
| 483 | public static class LeapYearPatternType implements Serializable { |
| 484 | /** Serialization lock */ |
| 485 | private static final long serialVersionUID = 26581275372698L; |
| 486 | // /** Leap year raw data encoded into bits. */ |
| 487 | // private static final int[][] LEAP_YEARS = { |
| 488 | // {2, 5, 7, 10, 13, 15, 18, 21, 24, 26, 29}, // 623158436 |
| 489 | // {2, 5, 7, 10, 13, 16, 18, 21, 24, 26, 29}, // 623191204 |
| 490 | // {2, 5, 8, 10, 13, 16, 19, 21, 24, 27, 29}, // 690562340 |
| 491 | // {0, 2, 5, 8, 11, 13, 16, 19, 21, 24, 27}, // 153692453 |
| 492 | // }; |
| 493 | |
| 494 | /** The index. */ |
| 495 | final byte index; |
| 496 | /** The leap year pattern, a bit-based 1=true pattern. */ |
| 497 | final int pattern; |
| 498 | |
| 499 | /** |
| 500 | * Constructor. |
| 501 | * This constructor takes a bit pattern where bits 0-29 correspond |
| 502 | * to years 0-29 in the 30 year Islamic cycle of years. This allows |
| 503 | * a highly efficient lookup by bit-matching. |
| 504 | * |
| 505 | * @param index the index |
| 506 | * @param pattern the bit pattern |
| 507 | */ |
| 508 | LeapYearPatternType(int index, int pattern) { |
| 509 | super(); |
| 510 | this.index = (byte) index; |
| 511 | this.pattern = pattern; |
| 512 | } |
| 513 | |
| 514 | /** |
| 515 | * Is the year a leap year. |
| 516 | * @param year the year to query |
| 517 | * @return true if leap |
| 518 | */ |
| 519 | boolean isLeapYear(int year) { |
| 520 | int key = 1 << (year % 30); |
| 521 | return ((pattern & key) > 0); |
| 522 | } |
| 523 | |
| 524 | /** |
| 525 | * Ensure a singleton is returned if possible. |
| 526 | * @return the singleton instance |
| 527 | */ |
| 528 | private Object readResolve() { |
| 529 | switch (index) { |
| 530 | case 0: |
| 531 | return LEAP_YEAR_15_BASED; |
| 532 | case 1: |
| 533 | return LEAP_YEAR_16_BASED; |
| 534 | case 2: |
| 535 | return LEAP_YEAR_INDIAN; |
| 536 | case 3: |
| 537 | return LEAP_YEAR_HABASH_AL_HASIB; |
| 538 | default: |
| 539 | return this; |
| 540 | } |
| 541 | } |
| 542 | } |
| 543 | } |