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Java > Open Source Codes > org > joda > time > chrono > JulianChronology


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.util.HashMap JavaDoc;
19 import java.util.Map JavaDoc;
20
21 import org.joda.time.Chronology;
22 import org.joda.time.DateTimeConstants;
23 import org.joda.time.DateTimeFieldType;
24 import org.joda.time.DateTimeZone;
25 import org.joda.time.IllegalFieldValueException;
26 import org.joda.time.field.SkipDateTimeField;
27
28 /**
29  * Implements a pure proleptic Julian calendar system, which defines every
30  * fourth year as leap. This implementation follows the leap year rule
31  * strictly, even for dates before 8 CE, where leap years were actually
32  * irregular. In the Julian calendar, year zero does not exist: 1 BCE is
33  * followed by 1 CE.
34  * <p>
35  * Although the Julian calendar did not exist before 45 BCE, this chronology
36  * assumes it did, thus it is proleptic. This implementation also fixes the
37  * start of the year at January 1.
38  * <p>
39  * JulianChronology is thread-safe and immutable.
40  *
41  * @see <a HREF="http://en.wikipedia.org/wiki/Julian_calendar">Wikipedia</a>
42  * @see GregorianChronology
43  * @see GJChronology
44  *
45  * @author Guy Allard
46  * @author Brian S O'Neill
47  * @author Stephen Colebourne
48  * @since 1.0
49  */
50 public final class JulianChronology extends BasicGJChronology {
51
52     /** Serialization lock */
53     private static final long serialVersionUID = -8731039522547897247L;
54
55     private static final long MILLIS_PER_YEAR =
56         (long) (365.25 * DateTimeConstants.MILLIS_PER_DAY);
57
58     private static final long MILLIS_PER_MONTH =
59         (long) (365.25 * DateTimeConstants.MILLIS_PER_DAY / 12);
60
61     /** The lowest year that can be fully supported. */
62     private static final int MIN_YEAR = -292269054;
63
64     /** The highest year that can be fully supported. */
65     private static final int MAX_YEAR = 292272992;
66
67     /** Singleton instance of a UTC JulianChronology */
68     private static final JulianChronology INSTANCE_UTC;
69
70     /** Cache of zone to chronology arrays */
71     private static final Map JavaDoc cCache = new HashMap JavaDoc();
72
73     static {
74         INSTANCE_UTC = getInstance(DateTimeZone.UTC);
75     }
76
77     static int adjustYearForSet(int year) {
78         if (year <= 0) {
79             if (year == 0) {
80                 throw new IllegalFieldValueException
81                     (DateTimeFieldType.year(), new Integer JavaDoc(year), null, null);
82             }
83             year++;
84         }
85         return year;
86     }
87
88     /**
89      * Gets an instance of the JulianChronology.
90      * The time zone of the returned instance is UTC.
91      *
92      * @return a singleton UTC instance of the chronology
93      */
94     public static JulianChronology getInstanceUTC() {
95         return INSTANCE_UTC;
96     }
97
98     /**
99      * Gets an instance of the JulianChronology in the default time zone.
100      *
101      * @return a chronology in the default time zone
102      */
103     public static JulianChronology getInstance() {
104         return getInstance(DateTimeZone.getDefault(), 4);
105     }
106
107     /**
108      * Gets an instance of the JulianChronology in the given time zone.
109      *
110      * @param zone the time zone to get the chronology in, null is default
111      * @return a chronology in the specified time zone
112      */
113     public static JulianChronology getInstance(DateTimeZone zone) {
114         return getInstance(zone, 4);
115     }
116
117     /**
118      * Gets an instance of the JulianChronology in the given time zone.
119      *
120      * @param zone the time zone to get the chronology in, null is default
121      * @param minDaysInFirstWeek minimum number of days in first week of the year; default is 4
122      * @return a chronology in the specified time zone
123      */
124     public static JulianChronology getInstance(DateTimeZone zone, int minDaysInFirstWeek) {
125         if (zone == null) {
126             zone = DateTimeZone.getDefault();
127         }
128         JulianChronology chrono;
129         synchronized (cCache) {
130             JulianChronology[] chronos = (JulianChronology[]) cCache.get(zone);
131             if (chronos == null) {
132                 chronos = new JulianChronology[7];
133                 cCache.put(zone, chronos);
134             }
135             try {
136                 chrono = chronos[minDaysInFirstWeek - 1];
137             } catch (ArrayIndexOutOfBoundsException JavaDoc e) {
138                 throw new IllegalArgumentException JavaDoc
139                     ("Invalid min days in first week: " + minDaysInFirstWeek);
140             }
141             if (chrono == null) {
142                 if (zone == DateTimeZone.UTC) {
143                     chrono = new JulianChronology(null, null, minDaysInFirstWeek);
144                 } else {
145                     chrono = getInstance(DateTimeZone.UTC, minDaysInFirstWeek);
146                     chrono = new JulianChronology
147                         (ZonedChronology.getInstance(chrono, zone), null, minDaysInFirstWeek);
148                 }
149                 chronos[minDaysInFirstWeek - 1] = chrono;
150             }
151         }
152         return chrono;
153     }
154
155     // Constructors and instance variables
156 //-----------------------------------------------------------------------
157
158     /**
159      * Restricted constructor
160      */
161     JulianChronology(Chronology base, Object JavaDoc param, int minDaysInFirstWeek) {
162         super(base, param, minDaysInFirstWeek);
163     }
164
165     /**
166      * Serialization singleton
167      */
168     private Object JavaDoc readResolve() {
169         Chronology base = getBase();
170         int minDays = getMinimumDaysInFirstWeek();
171         minDays = (minDays == 0 ? 4 : minDays); // handle rename of BaseGJChronology
172 return base == null ?
173                 getInstance(DateTimeZone.UTC, minDays) :
174                     getInstance(base.getZone(), minDays);
175     }
176
177     // Conversion
178 //-----------------------------------------------------------------------
179 /**
180      * Gets the Chronology in the UTC time zone.
181      *
182      * @return the chronology in UTC
183      */
184     public Chronology withUTC() {
185         return INSTANCE_UTC;
186     }
187
188     /**
189      * Gets the Chronology in a specific time zone.
190      *
191      * @param zone the zone to get the chronology in, null is default
192      * @return the chronology
193      */
194     public Chronology withZone(DateTimeZone zone) {
195         if (zone == null) {
196             zone = DateTimeZone.getDefault();
197         }
198         if (zone == getZone()) {
199             return this;
200         }
201         return getInstance(zone);
202     }
203
204     long getDateMidnightMillis(int year, int monthOfYear, int dayOfMonth)
205         throws IllegalArgumentException JavaDoc
206     {
207         return super.getDateMidnightMillis(adjustYearForSet(year), monthOfYear, dayOfMonth);
208     }
209
210     boolean isLeapYear(int year) {
211         return (year & 3) == 0;
212     }
213
214     long calculateFirstDayOfYearMillis(int year) {
215         // Java epoch is 1970-01-01 Gregorian which is 1969-12-19 Julian.
216 // Calculate relative to the nearest leap year and account for the
217 // difference later.
218
219         int relativeYear = year - 1968;
220         int leapYears;
221         if (relativeYear <= 0) {
222             // Add 3 before shifting right since /4 and >>2 behave differently
223 // on negative numbers.
224 leapYears = (relativeYear + 3) >> 2;
225         } else {
226             leapYears = relativeYear >> 2;
227             // For post 1968 an adjustment is needed as jan1st is before leap day
228 if (!isLeapYear(year)) {
229                 leapYears++;
230             }
231         }
232         
233         long millis = (relativeYear * 365L + leapYears) * (long)DateTimeConstants.MILLIS_PER_DAY;
234
235         // Adjust to account for difference between 1968-01-01 and 1969-12-19.
236
237         return millis - (366L + 352) * DateTimeConstants.MILLIS_PER_DAY;
238     }
239
240     int getMinYear() {
241         return MIN_YEAR;
242     }
243
244     int getMaxYear() {
245         return MAX_YEAR;
246     }
247
248     long getAverageMillisPerYear() {
249         return MILLIS_PER_YEAR;
250     }
251
252     long getAverageMillisPerYearDividedByTwo() {
253         return MILLIS_PER_YEAR / 2;
254     }
255
256     long getAverageMillisPerMonth() {
257         return MILLIS_PER_MONTH;
258     }
259
260     long getApproxMillisAtEpochDividedByTwo() {
261         return (1969L * MILLIS_PER_YEAR + 352L * DateTimeConstants.MILLIS_PER_DAY) / 2;
262     }
263
264     protected void assemble(Fields fields) {
265         if (getBase() == null) {
266             super.assemble(fields);
267             // Julian chronology has no year zero.
268 fields.year = new SkipDateTimeField(this, fields.year);
269             fields.weekyear = new SkipDateTimeField(this, fields.weekyear);
270         }
271     }
272
273 }
274
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