Compute the day of the year that Easter falls on. Java code example - Click here to copy ->>>

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Code:



 

/*

 * Copyright (c) Ian F. Darwin, http://www.darwinsys.com/, 1996-2002.

 * All rights reserved. Software written by Ian F. Darwin and others.

 * $Id: LICENSE,v 1.8 2004/02/09 03:33:38 ian Exp $

*/



import java.util.*;

import java.applet.*;



/** Easter - compute the day on which Easter falls.

 *

 * In the Christian religion, Easter is possibly the most important holiday

 * of the year, so getting its date <I>just so</I> is worthwhile.

 *

 * @author: Ian F. Darwin, http://www.darwinsys.com/,

 * based on a detailed algorithm in Knuth, vol 1, pg 155.

 *

 * @Version: $Id: Easter.java,v 1.5 2004/02/09 03:33:46 ian Exp $

 * Written in C, Toronto, 1988. Java version 1996.

 *

 * @Note: It's not proven correct, although it gets the right answer for

 * years around the present.

 */

public class Easter {



   /* Compute the day of the year that Easter falls on.

    * Step names E1 E2 etc., are direct references to Knuth, Vol 1, p 155.

    * @exception IllegalArgumentexception If the year is before 1582 (since the

    *       algorithm only works on the Gregorian calendar).

    */

   public static final Calendar findHolyDay(int year) {

      if (year <= 1582) {

         throw new IllegalArgumentException("Algorithm invalid before April 1583");

      }

      int golden, century, x, z, d, epact, n;



      golden = (year % 19) + 1;   /* E1: metonic cycle */

      century = (year / 100) + 1;   /* E2: e.g. 1984 was in 20th C */

      x = (3*century/4) - 12;      /* E3: leap year correction */

      z = ((8*century+5) / 25) -5;    /* E3: sync with moon's orbit */

      d = (5*year/4) - x - 10;

      epact = (11*golden + 20 + z - x) % 30; /* E5: epact */

      if ((epact == 25 && golden > 11) || epact == 24)

         epact++;

      n = 44 - epact;

      n += 30 * (n < 21?1:0);      /* E6: */

      n += 7 - ((d+n)%7);

      if (n>31)         /* E7: */

         return new GregorianCalendar(year, 4-1, n-31);   /* April */

      else

         return  new GregorianCalendar(year, 3-1, n);   /* March */

   }



   /** Main program, when used as a standalone application */

   public static void main(String[] argv) {



      if (argv.length == 0) {

         int thisYear = new GregorianCalendar().get(Calendar.YEAR);

         Calendar c = Easter.findHolyDay(thisYear);

         System.out.println( c.getTime());

      } else for (int i=0; i<argv.length; i++) {

         int year = 0;

         try {

            year = Integer.parseInt(argv[i]);

            System.out.println(Easter.findHolyDay(year).getTime());

         } catch (IllegalArgumentException e) {

            System.err.println("Year " + argv[i] + " invalid (" + e.getMessage() + ").");

         }

      }

   }

}