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 {@link #setCivil 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
* {@link com.ibm.icu.util.Calendar#getInstance(ULocale)} passing in a ULocale
* with the tag "@calendar=islamic" or "@calendar=islamic-civil".
IslamicCalendar using the current time
* in the default time zone with the default locale.
* @stable ICU 2.8
*/
public IslamicCalendar()
{
this(TimeZone.getDefault(), ULocale.getDefault());
}
/**
* Constructs an IslamicCalendar based on the current time
* in the given time zone with the default locale.
* @param zone the given time zone.
* @stable ICU 2.8
*/
public IslamicCalendar(TimeZone zone)
{
this(zone, ULocale.getDefault());
}
/**
* Constructs an IslamicCalendar based on the current time
* in the default time zone with the given locale.
*
* @param aLocale the given locale.
* @stable ICU 2.8
*/
public IslamicCalendar(Locale aLocale)
{
this(TimeZone.getDefault(), aLocale);
}
/**
* Constructs an IslamicCalendar based on the current time
* in the default time zone with the given locale.
*
* @param locale the given ulocale.
* @stable ICU 3.2
*/
public IslamicCalendar(ULocale locale)
{
this(TimeZone.getDefault(), locale);
}
/**
* Constructs an IslamicCalendar based on the current time
* in the given time zone with the given locale.
*
* @param zone the given time zone.
* @param aLocale the given locale.
* @stable ICU 2.8
*/
public IslamicCalendar(TimeZone zone, Locale aLocale)
{
super(zone, aLocale);
setTimeInMillis(System.currentTimeMillis());
}
/**
* Constructs an IslamicCalendar based on the current time
* in the given time zone with the given locale.
*
* @param zone the given time zone.
* @param locale the given ulocale.
* @stable ICU 3.2
*/
public IslamicCalendar(TimeZone zone, ULocale locale)
{
super(zone, locale);
setTimeInMillis(System.currentTimeMillis());
}
/**
* Constructs an IslamicCalendar with the given date set
* in the default time zone with the default locale.
*
* @param date The date to which the new calendar is set.
* @stable ICU 2.8
*/
public IslamicCalendar(Date date) {
super(TimeZone.getDefault(), ULocale.getDefault());
this.setTime(date);
}
/**
* Constructs an IslamicCalendar with the given date set
* in the default time zone with the default locale.
*
* @param year the value used to set the {@link #YEAR YEAR} time field in the calendar.
* @param month the value used to set the {@link #MONTH MONTH} time field in the calendar.
* Note that the month value is 0-based. e.g., 0 for Muharram.
* @param date the value used to set the {@link #DATE DATE} time field in the calendar.
* @stable ICU 2.8
*/
public IslamicCalendar(int year, int month, int date)
{
super(TimeZone.getDefault(), ULocale.getDefault());
this.set(Calendar.YEAR, year);
this.set(Calendar.MONTH, month);
this.set(Calendar.DATE, date);
}
/**
* Constructs an IslamicCalendar with the given date
* and time set for the default time zone with the default locale.
*
* @param year the value used to set the {@link #YEAR YEAR} time field in the calendar.
* @param month the value used to set the {@link #MONTH MONTH} time field in the calendar.
* Note that the month value is 0-based. e.g., 0 for Muharram.
* @param date the value used to set the {@link #DATE DATE} time field in the calendar.
* @param hour the value used to set the {@link #HOUR_OF_DAY HOUR_OF_DAY} time field
* in the calendar.
* @param minute the value used to set the {@link #MINUTE MINUTE} time field
* in the calendar.
* @param second the value used to set the {@link #SECOND SECOND} time field
* in the calendar.
* @stable ICU 2.8
*/
public IslamicCalendar(int year, int month, int date, int hour,
int minute, int second)
{
super(TimeZone.getDefault(), ULocale.getDefault());
this.set(Calendar.YEAR, year);
this.set(Calendar.MONTH, month);
this.set(Calendar.DATE, date);
this.set(Calendar.HOUR_OF_DAY, hour);
this.set(Calendar.MINUTE, minute);
this.set(Calendar.SECOND, second);
}
/**
* Determines whether this object uses the fixed-cycle Islamic civil calendar
* or an approximation of the religious, astronomical calendar.
*
* @param beCivil true to use the civil calendar,
* false to use the astronomical calendar.
* @stable ICU 2.8
*/
public void setCivil(boolean beCivil)
{
if (civil != beCivil) {
// The fields of the calendar will become invalid, because the calendar
// rules are different
long m = getTimeInMillis();
civil = beCivil;
clear();
setTimeInMillis(m);
}
}
/**
* Returns true if this object is using the fixed-cycle civil
* calendar, or false if using the religious, astronomical
* calendar.
* @stable ICU 2.8
*/
public boolean isCivil() {
return civil;
}
//-------------------------------------------------------------------------
// Minimum / Maximum access functions
//-------------------------------------------------------------------------
// Note: Current IslamicCalendar implementation does not work
// well with negative years.
private static final int LIMITS[][] = {
// Minimum Greatest Least Maximum
// Minimum Maximum
{ 0, 0, 0, 0}, // ERA
{ 1, 1, 5000000, 5000000}, // YEAR
{ 0, 0, 11, 11}, // MONTH
{ 1, 1, 50, 51}, // WEEK_OF_YEAR
{/* */}, // WEEK_OF_MONTH
{ 1, 1, 29, 30}, // DAY_OF_MONTH
{ 1, 1, 354, 355}, // DAY_OF_YEAR
{/* */}, // DAY_OF_WEEK
{ -1, -1, 5, 5}, // DAY_OF_WEEK_IN_MONTH
{/* */}, // AM_PM
{/* */}, // HOUR
{/* */}, // HOUR_OF_DAY
{/* */}, // MINUTE
{/* */}, // SECOND
{/* */}, // MILLISECOND
{/* */}, // ZONE_OFFSET
{/* */}, // DST_OFFSET
{ 1, 1, 5000000, 5000000}, // YEAR_WOY
{/* */}, // DOW_LOCAL
{ 1, 1, 5000000, 5000000}, // EXTENDED_YEAR
{/* */}, // JULIAN_DAY
{/* */}, // MILLISECONDS_IN_DAY
};
/**
* @stable ICU 2.8
*/
protected int handleGetLimit(int field, int limitType) {
return LIMITS[field][limitType];
}
//-------------------------------------------------------------------------
// Assorted calculation utilities
//
// Unused code - Alan 2003-05
// /**
// * Find the day of the week for a given day
// *
// * @param day The # of days since the start of the Islamic calendar.
// */
// // private and uncalled, perhaps not used yet?
// private static final int absoluteDayToDayOfWeek(long day)
// {
// // Calculate the day of the week.
// // This relies on the fact that the epoch was a Thursday.
// int dayOfWeek = (int)(day + THURSDAY) % 7 + SUNDAY;
// if (dayOfWeek < 0) {
// dayOfWeek += 7;
// }
// return dayOfWeek;
// }
/**
* Determine whether a year is a leap year in the Islamic civil calendar
*/
private final static boolean civilLeapYear(int year)
{
return (14 + 11 * year) % 30 < 11;
}
/**
* Return the day # on which the given year starts. Days are counted
* from the Hijri epoch, origin 0.
*/
private long yearStart(int year) {
if (civil) {
return (year-1)*354 + (long)Math.floor((3+11*year)/30.0);
} else {
return trueMonthStart(12*(year-1));
}
}
/**
* Return the day # on which the given month starts. Days are counted
* from the Hijri epoch, origin 0.
*
* @param year The hijri year
* @param month The hijri month, 0-based
*/
private long monthStart(int year, int month) {
if (civil) {
return (long)Math.ceil(29.5*month)
+ (year-1)*354 + (long)Math.floor((3+11*year)/30.0);
} else {
return trueMonthStart(12*(year-1) + month);
}
}
/**
* Find the day number on which a particular month of the true/lunar
* Islamic calendar starts.
*
* @param month The month in question, origin 0 from the Hijri epoch
*
* @return The day number on which the given month starts.
*/
private static final long trueMonthStart(long month)
{
long start = cache.get(month);
if (start == CalendarCache.EMPTY)
{
// Make a guess at when the month started, using the average length
long origin = HIJRA_MILLIS
+ (long)Math.floor(month * CalendarAstronomer.SYNODIC_MONTH) * ONE_DAY;
double age = moonAge(origin);
if (moonAge(origin) >= 0) {
// The month has already started
do {
origin -= ONE_DAY;
age = moonAge(origin);
} while (age >= 0);
}
else {
// Preceding month has not ended yet.
do {
origin += ONE_DAY;
age = moonAge(origin);
} while (age < 0);
}
start = (origin - HIJRA_MILLIS) / ONE_DAY + 1;
cache.put(month, start);
}
return start;
}
/**
* Return the "age" of the moon at the given time; this is the difference
* in ecliptic latitude between the moon and the sun. This method simply
* calls CalendarAstronomer.moonAge, converts to degrees,
* and adjusts the resultto be in the range [-180, 180].
*
* @param time The time at which the moon's age is desired,
* in millis since 1/1/1970.
*/
static final double moonAge(long time)
{
double age = 0;
synchronized(astro) {
astro.setTime(time);
age = astro.getMoonAge();
}
// Convert to degrees and normalize...
age = age * 180 / Math.PI;
if (age > 180) {
age = age - 360;
}
return age;
}
//-------------------------------------------------------------------------
// Internal data....
//
// And an Astronomer object for the moon age calculations
private static CalendarAstronomer astro = new CalendarAstronomer();
private static CalendarCache cache = new CalendarCache();
/**
* true if this object uses the fixed-cycle Islamic civil calendar,
* and false if it approximates the true religious calendar using
* astronomical calculations for the time of the new moon.
*
* @serial
*/
private boolean civil = true;
//----------------------------------------------------------------------
// Calendar framework
//----------------------------------------------------------------------
/**
* Return the length (in days) of the given month.
*
* @param extendedYear The hijri year
* @param month The hijri month, 0-based
* @stable ICU 2.8
*/
protected int handleGetMonthLength(int extendedYear, int month) {
int length = 0;
if (civil) {
length = 29 + (month+1) % 2;
if (month == DHU_AL_HIJJAH && civilLeapYear(extendedYear)) {
length++;
}
} else {
month = 12*(extendedYear-1) + month;
length = (int)( trueMonthStart(month+1) - trueMonthStart(month) );
}
return length;
}
/**
* Return the number of days in the given Islamic year
* @stable ICU 2.8
*/
protected int handleGetYearLength(int extendedYear) {
if (civil) {
return 354 + (civilLeapYear(extendedYear) ? 1 : 0);
} else {
int month = 12*(extendedYear-1);
return (int)(trueMonthStart(month + 12) - trueMonthStart(month));
}
}
//-------------------------------------------------------------------------
// Functions for converting from field values to milliseconds....
//-------------------------------------------------------------------------
// Return JD of start of given month/year
/**
* @stable ICU 2.8
*/
protected int handleComputeMonthStart(int eyear, int month, boolean useMonth) {
return (int) monthStart(eyear, month) + 1948439;
}
//-------------------------------------------------------------------------
// Functions for converting from milliseconds to field values
//-------------------------------------------------------------------------
/**
* @stable ICU 2.8
*/
protected int handleGetExtendedYear() {
int year;
if (newerField(EXTENDED_YEAR, YEAR) == EXTENDED_YEAR) {
year = internalGet(EXTENDED_YEAR, 1); // Default to year 1
} else {
year = internalGet(YEAR, 1); // Default to year 1
}
return year;
}
/**
* Override Calendar to compute several fields specific to the Islamic
* calendar system. These are:
*
*