com.ibm.icu.util

Class IslamicCalendar

Implemented Interfaces:
Cloneable, Comparable, Serializable

public class IslamicCalendar
extends Calendar

IslamicCalendar is a subclass of Calendar that that implements the Islamic civil and religious calendars. It is used as the civil calendar in most of the Arab world and the liturgical calendar of the Islamic faith worldwide. This calendar is also known as the "Hijri" calendar, since it starts at the time of Mohammed's emigration (or "hijra") to Medinah on Thursday, July 15, 622 AD (Julian).

The Islamic calendar is strictly lunar, and thus an Islamic year of twelve lunar months does not correspond to the solar year used by most other calendar systems, including the Gregorian. An Islamic year is, on average, about 354 days long, so each successive Islamic year starts about 11 days earlier in the corresponding Gregorian year.

Each month of the calendar starts when the new moon's crescent is visible at sunset. However, in order to keep the time fields in this class synchronized with those of the other calendars and with local clock time, we treat days and months as beginning at midnight, roughly 6 hours after the corresponding sunset.

There are two main variants of the Islamic calendar in existence. The first is the civil calendar, which uses a fixed cycle of alternating 29- and 30-day months, with a leap day added to the last month of 11 out of every 30 years. This calendar is easily calculated and thus predictable in advance, so it is used as the civil calendar in a number of Arab countries. This is the default behavior of a newly-created IslamicCalendar object.

The Islamic religious calendar, however, is based on the observation of the crescent moon. It is thus affected by the position at which the observations are made, seasonal variations in the time of sunset, the eccentricities of the moon's orbit, and even the weather at the observation site. This makes it impossible to calculate in advance, and it causes the start of a month in the religious calendar to differ from the civil calendar by up to three days.

Using astronomical calculations for the position of the sun and moon, the moon's illumination, and other factors, it is possible to determine the start of a lunar month with a fairly high degree of certainty. However, these calculations are extremely complicated and thus slow, so most algorithms, including the one used here, are only approximations of the true astronical calculations. At present, the approximations used in this class are fairly simplistic; they will be improved in later versions of the code.

The setCivil method determines which approach is used to determine the start of a month. By default, the fixed-cycle civil calendar is used. However, if setCivil(false) is called, an approximation of the true lunar calendar will be used.

This class should not be subclassed.

IslamicCalendar usually should be instantiated using Calendar.getInstance(ULocale) passing in a ULocale with the tag "@calendar=islamic" or "@calendar=islamic-civil".

Authors:
Laura Werner
Alan Liu
See Also:
GregorianCalendar, Calendar

Field Summary

static int
DHU_AL_HIJJAH
Constant for Dhu al-Hijjah, the 12th month of the Islamic year.
static int
DHU_AL_QIDAH
Constant for Dhu al-Qi'dah, the 11th month of the Islamic year.
static int
JUMADA_1
Constant for Jumada al-awwal or (Jumada I), the 5th month of the Islamic year.
static int
JUMADA_2
Constant for Jumada al-thani or (Jumada II), the 6th month of the Islamic year.
static int
MUHARRAM
Constant for Muharram, the 1st month of the Islamic year.
static int
RABI_1
Constant for Rabi' al-awwal (or Rabi' I), the 3rd month of the Islamic year.
static int
RABI_2
Constant for Rabi' al-thani or (Rabi' II), the 4th month of the Islamic year.
static int
RAJAB
Constant for Rajab, the 7th month of the Islamic year.
static int
RAMADAN
Constant for Ramadan, the 9th month of the Islamic year.
static int
SAFAR
Constant for Safar, the 2nd month of the Islamic year.
static int
SHABAN
Constant for Sha'ban, the 8th month of the Islamic year.
static int
SHAWWAL
Constant for Shawwal, the 10th month of the Islamic year.

Fields inherited from class com.ibm.icu.util.Calendar

AM, AM_PM, APRIL, AUGUST, BASE_FIELD_COUNT, DATE, DAY_OF_MONTH, DAY_OF_WEEK, DAY_OF_WEEK_IN_MONTH, DAY_OF_YEAR, DECEMBER, DOW_LOCAL, DST_OFFSET, EPOCH_JULIAN_DAY, ERA, EXTENDED_YEAR, FEBRUARY, FRIDAY, GREATEST_MINIMUM, HOUR, HOUR_OF_DAY, INTERNALLY_SET, JANUARY, JAN_1_1_JULIAN_DAY, JULIAN_DAY, JULY, JUNE, LEAST_MAXIMUM, MARCH, MAXIMUM, MAX_DATE, MAX_FIELD_COUNT, MAX_JULIAN, MAX_MILLIS, MAY, MILLISECOND, MILLISECONDS_IN_DAY, MINIMUM, MINIMUM_USER_STAMP, MINUTE, MIN_DATE, MIN_JULIAN, MIN_MILLIS, MONDAY, MONTH, NOVEMBER, OCTOBER, ONE_DAY, ONE_HOUR, ONE_MINUTE, ONE_SECOND, ONE_WEEK, PM, RESOLVE_REMAP, SATURDAY, SECOND, SEPTEMBER, SUNDAY, THURSDAY, TUESDAY, UNDECIMBER, UNSET, WEDNESDAY, WEEKDAY, WEEKEND, WEEKEND_CEASE, WEEKEND_ONSET, WEEK_OF_MONTH, WEEK_OF_YEAR, YEAR, YEAR_WOY, ZONE_OFFSET

Constructor Summary

IslamicCalendar()
Constructs a default IslamicCalendar using the current time in the default time zone with the default locale.
IslamicCalendar(Date date)
Constructs an IslamicCalendar with the given date set in the default time zone with the default locale.
IslamicCalendar(Locale aLocale)
Constructs an IslamicCalendar based on the current time in the default time zone with the given locale.
IslamicCalendar(TimeZone zone)
Constructs an IslamicCalendar based on the current time in the given time zone with the default locale.
IslamicCalendar(TimeZone zone, Locale aLocale)
Constructs an IslamicCalendar based on the current time in the given time zone with the given locale.
IslamicCalendar(TimeZone zone, ULocale locale)
Constructs an IslamicCalendar based on the current time in the given time zone with the given locale.
IslamicCalendar(ULocale locale)
Constructs an IslamicCalendar based on the current time in the default time zone with the given locale.
IslamicCalendar(int year, int month, int date)
Constructs an IslamicCalendar with the given date set in the default time zone with the default locale.
IslamicCalendar(int year, int month, int date, int hour, int minute, int second)
Constructs an IslamicCalendar with the given date and time set for the default time zone with the default locale.

Method Summary

String
getType()
Return the current Calendar type.
protected void
handleComputeFields(int julianDay)
Override Calendar to compute several fields specific to the Islamic calendar system.
protected int
handleComputeMonthStart(int eyear, int month, boolean useMonth)
protected int
handleGetExtendedYear()
protected int
handleGetLimit(int field, int limitType)
protected int
handleGetMonthLength(int extendedYear, int month)
Return the length (in days) of the given month.
protected int
handleGetYearLength(int extendedYear)
Return the number of days in the given Islamic year
boolean
isCivil()
Returns true if this object is using the fixed-cycle civil calendar, or false if using the religious, astronomical calendar.
void
setCivil(boolean beCivil)
Determines whether this object uses the fixed-cycle Islamic civil calendar or an approximation of the religious, astronomical calendar.

Methods inherited from class com.ibm.icu.util.Calendar

add, after, before, clear, clear, clone, compareTo, compareTo, complete, computeFields, computeGregorianFields, computeGregorianMonthStart, computeJulianDay, computeMillisInDay, computeTime, computeZoneOffset, equals, fieldDifference, fieldName, floorDivide, floorDivide, floorDivide, floorDivide, get, getActualMaximum, getActualMinimum, getAvailableLocales, getAvailableULocales, getDateTimeFormat, getDateTimeFormat, getDayOfWeekType, getDisplayName, getDisplayName, getFieldCount, getFieldResolutionTable, getFirstDayOfWeek, getGreatestMinimum, getGregorianDayOfMonth, getGregorianDayOfYear, getGregorianMonth, getGregorianYear, getInstance, getInstance, getInstance, getInstance, getInstance, getInstance, getLeastMaximum, getLimit, getLocale, getMaximum, getMinimalDaysInFirstWeek, getMinimum, getStamp, getTime, getTimeInMillis, getTimeZone, getType, getWeekendTransition, gregorianMonthLength, gregorianPreviousMonthLength, handleComputeFields, handleComputeJulianDay, handleComputeMonthStart, handleCreateFields, handleGetDateFormat, handleGetDateFormat, handleGetExtendedYear, handleGetLimit, handleGetMonthLength, handleGetYearLength, hashCode, internalGet, internalGet, internalGetTimeInMillis, internalSet, isEquivalentTo, isGregorianLeapYear, isLenient, isSet, isWeekend, isWeekend, julianDayToDayOfWeek, julianDayToMillis, millisToJulianDay, newerField, newestStamp, pinField, prepareGetActual, resolveFields, roll, roll, set, set, set, set, setFirstDayOfWeek, setLenient, setMinimalDaysInFirstWeek, setTime, setTimeInMillis, setTimeZone, toString, validateField, validateField, validateFields, weekNumber, weekNumber

Field Details

DHU_AL_HIJJAH

public static final int DHU_AL_HIJJAH
Constant for Dhu al-Hijjah, the 12th month of the Islamic year.
Field Value:
11

DHU_AL_QIDAH

public static final int DHU_AL_QIDAH
Constant for Dhu al-Qi'dah, the 11th month of the Islamic year.
Field Value:
10

JUMADA_1

public static final int JUMADA_1
Constant for Jumada al-awwal or (Jumada I), the 5th month of the Islamic year.
Field Value:
4

JUMADA_2

public static final int JUMADA_2
Constant for Jumada al-thani or (Jumada II), the 6th month of the Islamic year.
Field Value:
5

MUHARRAM

public static final int MUHARRAM
Constant for Muharram, the 1st month of the Islamic year.
Field Value:
0

RABI_1

public static final int RABI_1
Constant for Rabi' al-awwal (or Rabi' I), the 3rd month of the Islamic year.
Field Value:
2

RABI_2

public static final int RABI_2
Constant for Rabi' al-thani or (Rabi' II), the 4th month of the Islamic year.
Field Value:
3

RAJAB

public static final int RAJAB
Constant for Rajab, the 7th month of the Islamic year.
Field Value:
6

RAMADAN

public static final int RAMADAN
Constant for Ramadan, the 9th month of the Islamic year.
Field Value:
8

SAFAR

public static final int SAFAR
Constant for Safar, the 2nd month of the Islamic year.
Field Value:
1

SHABAN

public static final int SHABAN
Constant for Sha'ban, the 8th month of the Islamic year.
Field Value:
7

SHAWWAL

public static final int SHAWWAL
Constant for Shawwal, the 10th month of the Islamic year.
Field Value:
9

Constructor Details

IslamicCalendar

public IslamicCalendar()
Constructs a default IslamicCalendar using the current time in the default time zone with the default locale.

IslamicCalendar

public IslamicCalendar(Date date)
Constructs an IslamicCalendar with the given date set in the default time zone with the default locale.
Parameters:
date - The date to which the new calendar is set.

IslamicCalendar

public IslamicCalendar(Locale aLocale)
Constructs an IslamicCalendar based on the current time in the default time zone with the given locale.
Parameters:
aLocale - the given locale.

IslamicCalendar

public IslamicCalendar(TimeZone zone)
Constructs an IslamicCalendar based on the current time in the given time zone with the default locale.
Parameters:
zone - the given time zone.

IslamicCalendar

public IslamicCalendar(TimeZone zone,
                       Locale aLocale)
Constructs an IslamicCalendar based on the current time in the given time zone with the given locale.
Parameters:
zone - the given time zone.
aLocale - the given locale.

IslamicCalendar

public IslamicCalendar(TimeZone zone,
                       ULocale locale)
Constructs an IslamicCalendar based on the current time in the given time zone with the given locale.
Parameters:
zone - the given time zone.
locale - the given ulocale.

IslamicCalendar

public IslamicCalendar(ULocale locale)
Constructs an IslamicCalendar based on the current time in the default time zone with the given locale.
Parameters:
locale - the given ulocale.

IslamicCalendar

public IslamicCalendar(int year,
                       int month,
                       int date)
Constructs an IslamicCalendar with the given date set in the default time zone with the default locale.
Parameters:
year - the value used to set the YEAR time field in the calendar.
month - the value used to set the MONTH time field in the calendar. Note that the month value is 0-based. e.g., 0 for Muharram.
date - the value used to set the DATE time field in the calendar.

IslamicCalendar

public IslamicCalendar(int year,
                       int month,
                       int date,
                       int hour,
                       int minute,
                       int second)
Constructs an IslamicCalendar with the given date and time set for the default time zone with the default locale.
Parameters:
year - the value used to set the YEAR time field in the calendar.
month - the value used to set the MONTH time field in the calendar. Note that the month value is 0-based. e.g., 0 for Muharram.
date - the value used to set the DATE time field in the calendar.
hour - the value used to set the HOUR_OF_DAY time field in the calendar.
minute - the value used to set the MINUTE time field in the calendar.
second - the value used to set the SECOND time field in the calendar.

Method Details

getType

public String getType()
Return the current Calendar type.
Overrides:
getType in interface Calendar
Returns:
type of calendar (gregorian, etc.)

handleComputeFields

protected void handleComputeFields(int julianDay)
Override Calendar to compute several fields specific to the Islamic calendar system. These are:
  • ERA
  • YEAR
  • MONTH
  • DAY_OF_MONTH
  • DAY_OF_YEAR
  • EXTENDED_YEAR
The DAY_OF_WEEK and DOW_LOCAL fields are already set when this method is called. The getGregorianXxx() methods return Gregorian calendar equivalents for the given Julian day.
Overrides:
handleComputeFields in interface Calendar

handleComputeMonthStart

protected int handleComputeMonthStart(int eyear,
                                      int month,
                                      boolean useMonth)
Overrides:
handleComputeMonthStart in interface Calendar

handleGetExtendedYear

protected int handleGetExtendedYear()
Overrides:
handleGetExtendedYear in interface Calendar

handleGetLimit

protected int handleGetLimit(int field,
                             int limitType)
Overrides:
handleGetLimit in interface Calendar

handleGetMonthLength

protected int handleGetMonthLength(int extendedYear,
                                   int month)
Return the length (in days) of the given month.
Overrides:
handleGetMonthLength in interface Calendar
Parameters:
extendedYear - The hijri year
month - The hijri month, 0-based

handleGetYearLength

protected int handleGetYearLength(int extendedYear)
Return the number of days in the given Islamic year
Overrides:
handleGetYearLength in interface Calendar

isCivil

public boolean isCivil()
Returns true if this object is using the fixed-cycle civil calendar, or false if using the religious, astronomical calendar.

setCivil

public void setCivil(boolean beCivil)
Determines whether this object uses the fixed-cycle Islamic civil calendar or an approximation of the religious, astronomical calendar.
Parameters:
beCivil - true to use the civil calendar, false to use the astronomical calendar.

Copyright (c) 2006 IBM Corporation and others.