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


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.DateTimeZone;
24
25 /**
26  * Implements a pure proleptic Gregorian calendar system, which defines every
27  * fourth year as leap, unless the year is divisible by 100 and not by 400.
28  * This improves upon the Julian calendar leap year rule.
29  * <p>
30  * Although the Gregorian calendar did not exist before 1582 CE, this
31  * chronology assumes it did, thus it is proleptic. This implementation also
32  * fixes the start of the year at January 1, and defines the year zero.
33  * <p>
34  * GregorianChronology is thread-safe and immutable.
35  *
36  * @see <a HREF="http://en.wikipedia.org/wiki/Gregorian_calendar">Wikipedia</a>
37  * @see JulianChronology
38  * @see GJChronology
39  *
40  * @author Guy Allard
41  * @author Stephen Colebourne
42  * @author Brian S O'Neill
43  * @since 1.0
44  */
45 public final class GregorianChronology extends BasicGJChronology {
46
47     /** Serialization lock */
48     private static final long serialVersionUID = -861407383323710522L;
49
50     private static final long MILLIS_PER_YEAR =
51         (long) (365.2425 * DateTimeConstants.MILLIS_PER_DAY);
52
53     private static final long MILLIS_PER_MONTH =
54         (long) (365.2425 * DateTimeConstants.MILLIS_PER_DAY / 12);
55
56     private static final int DAYS_0000_TO_1970 = 719527;
57
58     /** The lowest year that can be fully supported. */
59     private static final int MIN_YEAR = -292275054;
60
61     /** The highest year that can be fully supported. */
62     private static final int MAX_YEAR = 292278993;
63
64     /** Singleton instance of a UTC GregorianChronology */
65     private static final GregorianChronology INSTANCE_UTC;
66
67     /** Cache of zone to chronology arrays */
68     private static final Map JavaDoc cCache = new HashMap JavaDoc();
69
70     static {
71         INSTANCE_UTC = getInstance(DateTimeZone.UTC);
72     }
73
74     /**
75      * Gets an instance of the GregorianChronology.
76      * The time zone of the returned instance is UTC.
77      *
78      * @return a singleton UTC instance of the chronology
79      */
80     public static GregorianChronology getInstanceUTC() {
81         return INSTANCE_UTC;
82     }
83
84     /**
85      * Gets an instance of the GregorianChronology in the default time zone.
86      *
87      * @return a chronology in the default time zone
88      */
89     public static GregorianChronology getInstance() {
90         return getInstance(DateTimeZone.getDefault(), 4);
91     }
92
93     /**
94      * Gets an instance of the GregorianChronology in the given time zone.
95      *
96      * @param zone the time zone to get the chronology in, null is default
97      * @return a chronology in the specified time zone
98      */
99     public static GregorianChronology getInstance(DateTimeZone zone) {
100         return getInstance(zone, 4);
101     }
102
103     /**
104      * Gets an instance of the GregorianChronology in the given time zone.
105      *
106      * @param zone the time zone to get the chronology in, null is default
107      * @param minDaysInFirstWeek minimum number of days in first week of the year; default is 4
108      * @return a chronology in the specified time zone
109      */
110     public static GregorianChronology getInstance(DateTimeZone zone, int minDaysInFirstWeek) {
111         if (zone == null) {
112             zone = DateTimeZone.getDefault();
113         }
114         GregorianChronology chrono;
115         synchronized (cCache) {
116             GregorianChronology[] chronos = (GregorianChronology[]) cCache.get(zone);
117             if (chronos == null) {
118                 chronos = new GregorianChronology[7];
119                 cCache.put(zone, chronos);
120             }
121             try {
122                 chrono = chronos[minDaysInFirstWeek - 1];
123             } catch (ArrayIndexOutOfBoundsException JavaDoc e) {
124                 throw new IllegalArgumentException JavaDoc
125                     ("Invalid min days in first week: " + minDaysInFirstWeek);
126             }
127             if (chrono == null) {
128                 if (zone == DateTimeZone.UTC) {
129                     chrono = new GregorianChronology(null, null, minDaysInFirstWeek);
130                 } else {
131                     chrono = getInstance(DateTimeZone.UTC, minDaysInFirstWeek);
132                     chrono = new GregorianChronology
133                         (ZonedChronology.getInstance(chrono, zone), null, minDaysInFirstWeek);
134                 }
135                 chronos[minDaysInFirstWeek - 1] = chrono;
136             }
137         }
138         return chrono;
139     }
140
141     // Constructors and instance variables
142 //-----------------------------------------------------------------------
143
144     /**
145      * Restricted constructor
146      */
147     private GregorianChronology(Chronology base, Object JavaDoc param, int minDaysInFirstWeek) {
148         super(base, param, minDaysInFirstWeek);
149     }
150
151     /**
152      * Serialization singleton
153      */
154     private Object JavaDoc readResolve() {
155         Chronology base = getBase();
156         int minDays = getMinimumDaysInFirstWeek();
157         minDays = (minDays == 0 ? 4 : minDays); // handle rename of BaseGJChronology
158 return base == null ?
159                 getInstance(DateTimeZone.UTC, minDays) :
160                     getInstance(base.getZone(), minDays);
161     }
162
163     // Conversion
164 //-----------------------------------------------------------------------
165 /**
166      * Gets the Chronology in the UTC time zone.
167      *
168      * @return the chronology in UTC
169      */
170     public Chronology withUTC() {
171         return INSTANCE_UTC;
172     }
173
174     /**
175      * Gets the Chronology in a specific time zone.
176      *
177      * @param zone the zone to get the chronology in, null is default
178      * @return the chronology
179      */
180     public Chronology withZone(DateTimeZone zone) {
181         if (zone == null) {
182             zone = DateTimeZone.getDefault();
183         }
184         if (zone == getZone()) {
185             return this;
186         }
187         return getInstance(zone);
188     }
189
190     protected void assemble(Fields fields) {
191         if (getBase() == null) {
192             super.assemble(fields);
193         }
194     }
195
196     boolean isLeapYear(int year) {
197         return ((year & 3) == 0) && ((year % 100) != 0 || (year % 400) == 0);
198     }
199
200     long calculateFirstDayOfYearMillis(int year) {
201         // Initial value is just temporary.
202 int leapYears = year / 100;
203         if (year < 0) {
204             // Add 3 before shifting right since /4 and >>2 behave differently
205 // on negative numbers. When the expression is written as
206 // (year / 4) - (year / 100) + (year / 400),
207 // it works for both positive and negative values, except this optimization
208 // eliminates two divisions.
209 leapYears = ((year + 3) >> 2) - leapYears + ((leapYears + 3) >> 2) - 1;
210         } else {
211             leapYears = (year >> 2) - leapYears + (leapYears >> 2);
212             if (isLeapYear(year)) {
213                 leapYears--;
214             }
215         }
216
217         return (year * 365L + (leapYears - DAYS_0000_TO_1970)) * DateTimeConstants.MILLIS_PER_DAY;
218     }
219
220     int getMinYear() {
221         return MIN_YEAR;
222     }
223
224     int getMaxYear() {
225         return MAX_YEAR;
226     }
227
228     long getAverageMillisPerYear() {
229         return MILLIS_PER_YEAR;
230     }
231
232     long getAverageMillisPerYearDividedByTwo() {
233         return MILLIS_PER_YEAR / 2;
234     }
235
236     long getAverageMillisPerMonth() {
237         return MILLIS_PER_MONTH;
238     }
239
240     long getApproxMillisAtEpochDividedByTwo() {
241         return (1970L * MILLIS_PER_YEAR) / 2;
242     }
243
244 }
245
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