net.time4j.calendar

Enum PersianAlgorithm

java.lang.Object

java.lang.Enum<PersianAlgorithm>

net.time4j.calendar.PersianAlgorithm

All Implemented Interfaces:

Serializable, Comparable<PersianAlgorithm>

public enum PersianAlgorithm
extends Enum<PersianAlgorithm>

Enumeration of different calculation methods for the Persian calendar.

Since:

3.33/4.28

Author:

Meno Hochschild

Enum Constant Summary

Enum Constants

Enum Constant and Description
ASTRONOMICAL Based on the astronomical calculation of vernal equinox as start of Persian year usually in the Iranian Standard time.
BIRASHK A popular proposal of Ahmad Birashk which uses a complex system of cycles and grand cycles.
BORKOWSKI Based on the work of the Polish astronomer Kazimierz Borkowski.
KHAYYAM Uses a 33-year-cycle to determine a simple leap year rule (discovered by Omar Khayyam).

Method Summary

Modifier and Type	Method and Description
static AttributeKey<PersianAlgorithm>	attribute() Format attribute which helps to resolve algorithmic differences between various Persian dates.
boolean	isLeapYear(int persianYear) Determines if given persian year is a leap year.
static PersianAlgorithm	valueOf(String name) Returns the enum constant of this type with the specified name.
static PersianAlgorithm[]	values() Returns an array containing the constants of this enum type, in the order they are declared.

Methods inherited from class java.lang.Enum

compareTo, equals, getDeclaringClass, hashCode, name, ordinal, toString, valueOf

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Enum Constant Detail

BORKOWSKI

public static final PersianAlgorithm BORKOWSKI

Based on the work of the Polish astronomer Kazimierz Borkowski.

This is the default and uses a refinement of the Khayyam 33-year-rule based on astronomical calculations for the Teheran mean time. However, users should keep following things in mind when discussing the possible errors:

• Borkowski uses the offset of +03:25:30 which deviates from the Iranian Standard Time +03:30. In addition, it is questionable if the historic ancestor of the Persian calendar has used any of these offsets in ancient times.
• The astronomical calculations are not published in detail but seem to deviate by several minutes in the far past or future compared with what we can derive from the work of the Belgian astronomer Jean Meeus.
• The delta-T-calculation is somehow simplistic compared with the more accurate formulas used in Time4J.
• The mean solar time is used. It is for debate if the Persian calendar is rather based on the apparent solar time.

KHAYYAM

public static final PersianAlgorithm KHAYYAM

Uses a 33-year-cycle to determine a simple leap year rule (discovered by Omar Khayyam).

If the remainder of the division of persian year by 33 is one of following numbers then and only then it is a leap year: 1, 5, 9, 13, 17, 22, 26, 30. The rule is correct for the Persian years 1178-1633 (gregorian: 1799-2254).

BIRASHK

public static final PersianAlgorithm BIRASHK

A popular proposal of Ahmad Birashk which uses a complex system of cycles and grand cycles.

It works for most years but sometimes it is not in agreement with the astronomical nature of the Persian calendar. For example, the year 2025 (gregorian) is expected to break this rule.

ASTRONOMICAL

public static final PersianAlgorithm ASTRONOMICAL

Based on the astronomical calculation of vernal equinox as start of Persian year usually in the Iranian Standard time.

The implementation works as follows:

• The vernal equinox is evaluated by AstronomicalSeason.inYear(int).
• The time zone offset is chosen as UTC+03:30 if not specified otherwise.
• If the apparent vernal equinox is after noon then the next day is the start of Persian year.
• The maximum supported Persian year is 2378.

Method Detail

values

public static PersianAlgorithm[] values()

Returns an array containing the constants of this enum type, in the order they are declared. This method may be used to iterate over the constants as follows:

for (PersianAlgorithm c : PersianAlgorithm.values())
    System.out.println(c);

Returns:

an array containing the constants of this enum type, in the order they are declared

valueOf

public static PersianAlgorithm valueOf(String name)

Returns the enum constant of this type with the specified name. The string must match exactly an identifier used to declare an enum constant in this type. (Extraneous whitespace characters are not permitted.)

Parameters:

name - the name of the enum constant to be returned.

Returns:

the enum constant with the specified name

Throws:

IllegalArgumentException - if this enum type has no constant with the specified name

NullPointerException - if the argument is null

attribute

public static AttributeKey<PersianAlgorithm> attribute()

Format attribute which helps to resolve algorithmic differences between various Persian dates.

Following example demonstrates the difference between the standard algorithm and the algorithm proposed by A. Birashk:

      PersianCalendar pcal = PersianCalendar.of(1403, 12, 30); // = 2025-03-20 (gregorian)
      ChronoFormatter<PersianCalendar> f =
          ChronoFormatter
              .ofPattern("dd.MM.yyyy G", PatternType.CLDR, Locale.ROOT, PersianCalendar.axis())
              .with(PersianAlgorithm.attribute(), PersianAlgorithm.BIRASHK);
      assertThat(f.parse("01.01.1404 AP"), is(pcal));
      assertThat(f.format(pcal), is("01.01.1404 AP"));
 

Standard value is: BORKOWSKI. It is also possible to use the astronomical algorithm in combination with an arbitrary timezone offset by setting the format attribute Attributes.TIMEZONE_ID to any ZonalOffset.

Returns:

format attribute key

isLeapYear

public boolean isLeapYear(int persianYear)

Determines if given persian year is a leap year.

Parameters:

persianYear - the persian year to be queried

Returns:

true if the year is a leap year else false

Throws:

IllegalArgumentException - if the year is out of range 1-3000