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- /* ========================================================================
- * JCommon : a free general purpose class library for the Java(tm) platform
- * ========================================================================
- *
- * (C) Copyright 2000-2005, by Object Refinery Limited and Contributors.
- *
- * Project Info: http://www.jfree.org/jcommon/index.html
- *
- * This library is free software; you can redistribute it and/or modify it
- * under the terms of the GNU Lesser General Public License as published by
- * the Free Software Foundation; either version 2.1 of the License, or
- * (at your option) any later version.
- *
- * This library is distributed in the hope that it will be useful, but
- * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
- * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
- * License for more details.
- *
- * You should have received a copy of the GNU Lesser General Public
- * License along with this library; if not, write to the Free Software
- * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
- * USA.
- *
- * [Java is a trademark or registered trademark of Sun Microsystems, Inc.
- * in the United States and other countries.]
- *
- * ---------------------
- * EasterSundayRule.java
- * ---------------------
- * (C) Copyright 2000-2003, by Object Refinery Limited.
- *
- * Original Author: David Gilbert (for Object Refinery Limited);
- * Contributor(s): -;
- *
- * $Id: EasterSundayRule.java,v 1.4 2005/11/16 15:58:40 taqua Exp $
- *
- * Changes (from 26-Oct-2001)
- * --------------------------
- * 26-Oct-2001 : Changed package to com.jrefinery.date.*;
- * 03-Oct-2002 : Fixed errors reported by Checkstyle (DG);
- * 01-Jun-2005 : Removed the explicit clonable declaration, it is declared
- * in the super class.
- */
- package org.jfree.date;
- /**
- * An annual date rule for Easter (Sunday). The algorithm used here was
- * obtained from a Calendar FAQ which can be found at:
- * <P>
- * <a href="http://www.tondering.dk/claus/calendar.html"
- * >http://www.tondering.dk/claus/calendar.html</a>.
- * <P>
- * It is based on an algorithm by Oudin (1940) and quoted in "Explanatory Supplement to the
- * Astronomical Almanac", P. Kenneth Seidelmann, editor.
- *
- * @author David Gilbert
- */
- public class EasterSundayRule extends AnnualDateRule {
- /**
- * Default constructor.
- */
- public EasterSundayRule() {
- }
- /**
- * Returns the date of Easter Sunday for the given year. See the class
- * description for the source of the algorithm.
- * <P>
- * This method supports the AnnualDateRule interface.
- *
- * @param year the year to check.
- *
- * @return the date of Easter Sunday for the given year.
- */
- public SerialDate getDate(final int year) {
- final int g = year % 19;
- final int c = year / 100;
- final int h = (c - c / 4 - (8 * c + 13) / 25 + 19 * g + 15) % 30;
- final int i = h - h / 28 * (1 - h / 28 * 29 / (h + 1) * (21 - g) / 11);
- final int j = (year + year / 4 + i + 2 - c + c / 4) % 7;
- final int l = i - j;
- final int month = 3 + (l + 40) / 44;
- final int day = l + 28 - 31 * (month / 4);
- return SerialDate.createInstance(day, month, year);
- }
- }
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