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1: /* ======================================================================== 2: * JCommon : a free general purpose class library for the Java(tm) platform 3: * ======================================================================== 4: * 5: * (C) Copyright 2000-2005, by Object Refinery Limited and Contributors. 6: * 7: * Project Info: http://www.jfree.org/jcommon/index.html 8: * 9: * This library is free software; you can redistribute it and/or modify it 10: * under the terms of the GNU Lesser General Public License as published by 11: * the Free Software Foundation; either version 2.1 of the License, or 12: * (at your option) any later version. 13: * 14: * This library is distributed in the hope that it will be useful, but 15: * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 16: * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public 17: * License for more details. 18: * 19: * You should have received a copy of the GNU Lesser General Public 20: * License along with this library; if not, write to the Free Software 21: * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, 22: * USA. 23: * 24: * [Java is a trademark or registered trademark of Sun Microsystems, Inc. 25: * in the United States and other countries.] 26: * 27: * --------------------- 28: * EasterSundayRule.java 29: * --------------------- 30: * (C) Copyright 2000-2003, by Object Refinery Limited. 31: * 32: * Original Author: David Gilbert (for Object Refinery Limited); 33: * Contributor(s): -; 34: * 35: * $Id: EasterSundayRule.java,v 1.4 2005/11/16 15:58:40 taqua Exp $ 36: * 37: * Changes (from 26-Oct-2001) 38: * -------------------------- 39: * 26-Oct-2001 : Changed package to com.jrefinery.date.*; 40: * 03-Oct-2002 : Fixed errors reported by Checkstyle (DG); 41: * 01-Jun-2005 : Removed the explicit clonable declaration, it is declared 42: * in the super class. 43: */ 44: 45: package org.jfree.date; 46: 47: /** 48: * An annual date rule for Easter (Sunday). The algorithm used here was 49: * obtained from a Calendar FAQ which can be found at: 50: * <P> 51: * <a href="http://www.tondering.dk/claus/calendar.html" 52: * >http://www.tondering.dk/claus/calendar.html</a>. 53: * <P> 54: * It is based on an algorithm by Oudin (1940) and quoted in "Explanatory Supplement to the 55: * Astronomical Almanac", P. Kenneth Seidelmann, editor. 56: * 57: * @author David Gilbert 58: */ 59: public class EasterSundayRule extends AnnualDateRule { 60: 61: /** 62: * Default constructor. 63: */ 64: public EasterSundayRule() { 65: } 66: 67: /** 68: * Returns the date of Easter Sunday for the given year. See the class 69: * description for the source of the algorithm. 70: * <P> 71: * This method supports the AnnualDateRule interface. 72: * 73: * @param year the year to check. 74: * 75: * @return the date of Easter Sunday for the given year. 76: */ 77: public SerialDate getDate(final int year) { 78: final int g = year % 19; 79: final int c = year / 100; 80: final int h = (c - c / 4 - (8 * c + 13) / 25 + 19 * g + 15) % 30; 81: final int i = h - h / 28 * (1 - h / 28 * 29 / (h + 1) * (21 - g) / 11); 82: final int j = (year + year / 4 + i + 2 - c + c / 4) % 7; 83: final int l = i - j; 84: final int month = 3 + (l + 40) / 44; 85: final int day = l + 28 - 31 * (month / 4); 86: return SerialDate.createInstance(day, month, year); 87: } 88: 89: }