| <?xml version="1.0" encoding="ISO-8859-1"?> | |
| <document> | |
| <properties> | |
| <title>Java date and time API - Coptic calendar system</title> | |
| <author>Stephen Colebourne</author> | |
| </properties> | |
| <body> | |
| <section name="Ethiopic calendar system"> | |
| <p> | |
| The Ethiopic calendar system is similiar to the | |
| <a href="cal_coptic.html">Coptic</a> calendar and based on that used in ancient Egypt. | |
| The calendar system is in use today in Ethiopia. | |
| </p> | |
| <p> | |
| The Ethiopic calendar system consists of 12 months of exactly 30 days, followed by | |
| a 5 or 6 day intercalary month making a year of 365 or 366 days. | |
| Leap years (6 day intercalary month) occur every 4 years without exception (as per the Julian calendar). | |
| They occur when the remainder left after dividing the Ethiopic year by four is 3. | |
| The Ethiopic year starts on Septamber 11th/12th depending on leap years. | |
| The epoch date for the calendar is 0008-08-29 (Julian), which therefore is 0001-01-01 (Ethiopic). | |
| The current era is 'EE' (Ethiopian Era). | |
| </p> | |
| <p> | |
| Joda-Time implements the rules described above. | |
| We model the 5 or 6 day intercalary month as month 13. | |
| We also prevent the entry of dates before year 1. | |
| </p> | |
| <p> | |
| References | |
| <ul> | |
| <li>Calendrical Calculations - Millenium Edition - ISBN 0521777526</li> | |
| <li><a href="http://en.wikipedia.org/wiki/Ethiopian_calendar">Wikipedia - Ethiopic Calendar</a></li> | |
| </ul> | |
| </p> | |
| </section> | |
| <section name="Using Ethiopic chronology in Joda-Time"> | |
| <p> | |
| Within Joda-Time the Ethiopic calendar system can be used by obtaining an | |
| instance of <a href="apidocs/org/joda/time/chrono/EthiopicChronology.html">EthiopicChronology</a>. | |
| This is normally created via the | |
| <a href="apidocs/org/joda/time/chrono/EthiopicChronology.html#getInstance()">EthiopicChronology.getInstance()</a> factory. | |
| The chronology is then passed into the constructors of the main date and time classes. | |
| </p> | |
| <source> | |
| // setup date object for midday on May Day 2004 (ISO year 2004) | |
| DateTime dtISO = new DateTime(2004, 5, 1, 12, 0, 0, 0); | |
| // find out what the same instant is using the Ethiopic Chronology | |
| DateTime dtEthiopic = dtISO.withChronology(EthiopicChronology.getInstance()); | |
| </source> | |
| </section> | |
| </body> | |
| </document> |