Years ago I posted the Calculating Erev Pesach Zmanim that discussed the addition of sof zman achilas chametz and sof zman biur chametz times to the API. Based on a request on the KosherJava project’s GitHub repository, a new isTaanisBechoros() method was added to the API. The Taanis Bechoros fast day usually occurs on Erev Pesach, but in years like this year (5781/2021) when Erev Pesach occurs on Shabbos, the fast is moved back to Thursday the 12th of Nissan. Erev Pesach occurs on Shabbos an average of once every 10 years. The frequency of such occurrences ranges from 3 to 20 years. It will next occur in the year 5785/2025, followed 20 years later in the year 5805/2045. The code is included in the new v2.2.0 release of the KosherJava zmanim library. The following code sample shows the basic usage of the new method.
JewishCalendar jd = new JewishCalendar(); HebrewDateFormatter hdf = new HebrewDateFormatter(); jd.setJewishDate(5781, JewishDate.NISSAN, 12); System.out.println(jd.isTaanisBechoros());