gregoriancalendar.java

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/*
 * @(#)GregorianCalendar.java	1.29 98/02/02
 *
 * (C) Copyright Taligent, Inc. 1996-1997 - All Rights Reserved
 * (C) Copyright IBM Corp. 1996-1997 - All Rights Reserved
 *
 * Portions copyright (c) 1996 Sun Microsystems, Inc. All Rights Reserved.
 *
 *   The original version of this source code and documentation is copyrighted
 * and owned by Taligent, Inc., a wholly-owned subsidiary of IBM. These
 * materials are provided under terms of a License Agreement between Taligent
 * and Sun. This technology is protected by multiple US and International
 * patents. This notice and attribution to Taligent may not be removed.
 *   Taligent is a registered trademark of Taligent, Inc.
 *
 * Permission to use, copy, modify, and distribute this software
 * and its documentation for NON-COMMERCIAL purposes and without
 * fee is hereby granted provided that this copyright notice
 * appears in all copies. Please refer to the file "copyright.html"
 * for further important copyright and licensing information.
 *
 * SUN MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE SUITABILITY OF
 * THE SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
 * TO THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
 * PARTICULAR PURPOSE, OR NON-INFRINGEMENT. SUN SHALL NOT BE LIABLE FOR
 * ANY DAMAGES SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING OR
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 *
 */

package java.util;

/**
 * <code>GregorianCalendar</code> is a concrete subclass of
 * <a href="java.util.Calendar.html"><code>Calendar</code></a>
 * and provides the standard calendar used by most of the world.
 *
 * <p>
 * The standard (Gregorian) calendar has 2 eras, BC and AD.
 *
 * <p>
 * This implementation handles a single discontinuity, which corresponds
 * by default to the date the Gregorian calendar was instituted (October 15,
 * 1582 in some countries, later in others). This cutover date may be changed
 * by the caller.
 *
 * <p>
 * Prior to the institution of the Gregorian calendar, New Year's Day was
 * March 25. To avoid confusion, this calendar always uses January 1. A manual
 * adjustment may be made if desired for dates that are prior to the Gregorian
 * changeover and which fall between January 1 and March 24.
 *
 * <p>
 * <strong>Example:</strong>
 * <blockquote>
 * <pre>
 * // get the supported ids for GMT-08:00 (Pacific Standard Time)
 * String[] ids = TimeZone.getAvailableIDs(-8 * 60 * 60 * 1000);
 * // if no ids were returned, something is wrong. get out.
 * if (ids.length == 0)
 *     System.exit(0);
 *
 *  // begin output
 * System.out.println("Current Time");
 *
 * // create a Pacific Standard Time time zone
 * SimpleTimeZone pdt = new SimpleTimeZone(-8 * 60 * 60 * 1000, ids[0]);
 *
 * // set up rules for daylight savings time
 * pdt.setStartRule(Calendar.APRIL, 1, Calendar.SUNDAY, 2 * 60 * 60 * 1000);
 * pdt.setEndRule(Calendar.OCTOBER, -1, Calendar.SUNDAY, 2 * 60 * 60 * 1000);
 *
 * // create a GregorianCalendar with the Pacific Daylight time zone
 * // and the current date and time
 * Calendar calendar = new GregorianCalendar(pdt);
 * Date trialTime = new Date();
 * calendar.setTime(trialTime);
 *
 * // print out a bunch of interesting things
 * System.out.println("ERA: " + calendar.get(Calendar.ERA));
 * System.out.println("YEAR: " + calendar.get(Calendar.YEAR));
 * System.out.println("MONTH: " + calendar.get(Calendar.MONTH));
 * System.out.println("WEEK_OF_YEAR: " + calendar.get(Calendar.WEEK_OF_YEAR));
 * System.out.println("WEEK_OF_MONTH: " + calendar.get(Calendar.WEEK_OF_MONTH));
 * System.out.println("DATE: " + calendar.get(Calendar.DATE));
 * System.out.println("DAY_OF_MONTH: " + calendar.get(Calendar.DAY_OF_MONTH));
 * System.out.println("DAY_OF_YEAR: " + calendar.get(Calendar.DAY_OF_YEAR));
 * System.out.println("DAY_OF_WEEK: " + calendar.get(Calendar.DAY_OF_WEEK));
 * System.out.println("DAY_OF_WEEK_IN_MONTH: "
 *                    + calendar.get(Calendar.DAY_OF_WEEK_IN_MONTH));
 * System.out.println("AM_PM: " + calendar.get(Calendar.AM_PM));
 * System.out.println("HOUR: " + calendar.get(Calendar.HOUR));
 * System.out.println("HOUR_OF_DAY: " + calendar.get(Calendar.HOUR_OF_DAY));
 * System.out.println("MINUTE: " + calendar.get(Calendar.MINUTE));
 * System.out.println("SECOND: " + calendar.get(Calendar.SECOND));
 * System.out.println("MILLISECOND: " + calendar.get(Calendar.MILLISECOND));
 * System.out.println("ZONE_OFFSET: "
 *                    + (calendar.get(Calendar.ZONE_OFFSET)/(60*60*1000)));
 * System.out.println("DST_OFFSET: "
 *                    + (calendar.get(Calendar.DST_OFFSET)/(60*60*1000)));

 * System.out.println("Current Time, with hour reset to 3");
 * calendar.clear(Calendar.HOUR_OF_DAY); // so doesn't override
 * calendar.set(Calendar.HOUR, 3);
 * System.out.println("ERA: " + calendar.get(Calendar.ERA));
 * System.out.println("YEAR: " + calendar.get(Calendar.YEAR));
 * System.out.println("MONTH: " + calendar.get(Calendar.MONTH));
 * System.out.println("WEEK_OF_YEAR: " + calendar.get(Calendar.WEEK_OF_YEAR));
 * System.out.println("WEEK_OF_MONTH: " + calendar.get(Calendar.WEEK_OF_MONTH));
 * System.out.println("DATE: " + calendar.get(Calendar.DATE));
 * System.out.println("DAY_OF_MONTH: " + calendar.get(Calendar.DAY_OF_MONTH));
 * System.out.println("DAY_OF_YEAR: " + calendar.get(Calendar.DAY_OF_YEAR));
 * System.out.println("DAY_OF_WEEK: " + calendar.get(Calendar.DAY_OF_WEEK));
 * System.out.println("DAY_OF_WEEK_IN_MONTH: "
 *                    + calendar.get(Calendar.DAY_OF_WEEK_IN_MONTH));
 * System.out.println("AM_PM: " + calendar.get(Calendar.AM_PM));
 * System.out.println("HOUR: " + calendar.get(Calendar.HOUR));
 * System.out.println("HOUR_OF_DAY: " + calendar.get(Calendar.HOUR_OF_DAY));
 * System.out.println("MINUTE: " + calendar.get(Calendar.MINUTE));
 * System.out.println("SECOND: " + calendar.get(Calendar.SECOND));
 * System.out.println("MILLISECOND: " + calendar.get(Calendar.MILLISECOND));
 * System.out.println("ZONE_OFFSET: "
 *        + (calendar.get(Calendar.ZONE_OFFSET)/(60*60*1000))); // in hours
 * System.out.println("DST_OFFSET: "
 *        + (calendar.get(Calendar.DST_OFFSET)/(60*60*1000))); // in hours
 * </pre>
 * </blockquote>
 *
 * @see          Calendar
 * @see          TimeZone
 * @version      1.29 02/02/98
 * @author       David Goldsmith, Mark Davis, Chen-Lieh Huang, Alan Liu
 */
public class GregorianCalendar extends Calendar {

    // Internal notes:
    // This algorithm is based on the one presented on pp. 10-12 of
    // "Numerical Recipes in C", William H. Press, et. al., Cambridge
    // University Press 1988, ISBN 0-521-35465-X.

    /**
     * Useful constant for GregorianCalendar.
     */
    public static final int BC = 0;
    /**
     * Useful constant for GregorianCalendar.
     */
    public static final int AD = 1;

    // Note that the Julian date used here is not a true Julian date, since
    // it is measured from midnight, not noon.

    private static final long julianDayOffset = 2440588;
    private static final int millisPerDay = 24 * 60 * 60 * 1000;
    private static final int NUM_DAYS[]
    = {0,31,59,90,120,151,181,212,243,273,304,334}; // 0-based, for day-in-year
    private static final int LEAP_NUM_DAYS[]
    = {0,31,60,91,121,152,182,213,244,274,305,335}; // 0-based, for day-in-year
    private static final int MONTH_LENGTH[]
    = {31,28,31,30,31,30,31,31,30,31,30,31}; // 0-based
    private static final int LEAP_MONTH_LENGTH[]
    = {31,29,31,30,31,30,31,31,30,31,30,31}; // 0-based

    // This is measured from the standard epoch, not in Julian Days.
    // Default is 00:00:00 local time, October 15, 1582.
    private long gregorianCutover = -12219292800000L;

    // The onset of the Julian calendar is 45 B.C.  The Julian day
    // number for the start of the year 45 B.C. is 1712653.  We compute
    // the Julian onset as epoch-based millis.  Note that this number is
    // useful for rough comparison purposes only; it's not exact. [LIU]
    private static long JULIAN_ONSET = (1712653 - julianDayOffset) * millisPerDay;

    // Useful millisecond constants
    private static final long ONE_SECOND = 1000;
    private static final long ONE_MINUTE = 60*ONE_SECOND;
    private static final long ONE_HOUR   = 60*ONE_MINUTE;
    private static final long ONE_DAY    = 24*ONE_HOUR;
    private static final long ONE_WEEK   = 7*ONE_DAY;

    // Useful inverses
    private static final float INV1 = 1/36524.25f;              /*ibm.7853*/
    private static final double INV2 = 1/365.25d;               /*ibm.7853*/
    private static final float INV3 = 1/30.6001f;               /*ibm.7853*/

    // Proclaim serialization compatiblity with JDK 1.1
    static final long serialVersionUID = -8125100834729963327L;

    /**
     * Converts time as milliseconds to Julian date.
     * @param millis the given milliseconds.
     * @return the Julian date number.
     */
    private static final long millisToJulianDay(long millis)
    {
        if (millis >= 0)
            return julianDayOffset + (millis / millisPerDay);
        else
            return julianDayOffset
                + ((millis - millisPerDay + 1) / millisPerDay);
    }

    /**
     * Converts Julian date to time as milliseconds.
     * @param julian the given Julian date number.
     * @return time as milliseconds.
     */
    private static final long julianDayToMillis(long julian)
    {
        return (julian - julianDayOffset) * millisPerDay;
    }

    /**
     * Constructs a default GregorianCalendar using the current time
     * in the default time zone with the default locale.
     */
    public GregorianCalendar()
    {
        this(TimeZone.getDefault(), Locale.getDefault());
    }

    /**
     * Constructs a GregorianCalendar based on the current time
     * in the given time zone with the default locale.
     * @param zone the given time zone.
     */
    public GregorianCalendar(TimeZone zone)
    {
        this(zone, Locale.getDefault());
    }

    /**
     * Constructs a GregorianCalendar based on the current time
     * in the default time zone with the given locale.
     * @param aLocale the given locale.
     */
    public GregorianCalendar(Locale aLocale)
    {
        this(TimeZone.getDefault(), aLocale);
    }

    /**
     * Constructs a GregorianCalendar based on the current time
     * in the given time zone with the given locale.
     * @param zone the given time zone.
     * @param aLocale the given locale.
     */
    public GregorianCalendar(TimeZone zone, Locale aLocale)
    {
        super(zone, aLocale);
        setTimeInMillis(System.currentTimeMillis());
    }

    /**
     * Constructs a GregorianCalendar with the given date set
     * in the default time zone with the default locale.
     * @param year the value used to set the YEAR time field in the calendar.
     * @param month the value used to set the MONTH time field in the calendar.
     * Month value is 0-based. e.g., 0 for January.
     * @param date the value used to set the DATE time field in the calendar.
     */
    public GregorianCalendar(int year, int month, int date)
    {
        super(TimeZone.getDefault(), Locale.getDefault());
        this.set(ERA, AD);
        this.set(YEAR, year);
        this.set(MONTH, month);
        this.set(DATE, date);
    }

    /**
     * Constructs a GregorianCalendar with the given date
     * and time set for the default time zone with the default locale.
     * @param year the value used to set the YEAR time field in the calendar.
     * @param month the value used to set the MONTH time field in the calendar.
     * Month value is 0-based. e.g., 0 for January.
     * @param date the value used to set the DATE time field in the calendar.
     * @param hour the value used to set the HOUR_OF_DAY time field
     * in the calendar.
     * @param minute the value used to set the MINUTE time field
     * in the calendar.
     */
    public GregorianCalendar(int year, int month, int date, int hour,
                             int minute)
    {
        super(TimeZone.getDefault(), Locale.getDefault());
        this.set(ERA, AD);
        this.set(YEAR, year);
        this.set(MONTH, month);
        this.set(DATE, date);
        this.set(HOUR_OF_DAY, hour);
        this.set(MINUTE, minute);
    }

    /**
     * Constructs a GregorianCalendar with the given date
     * and time set for the default time zone with the default locale.
     * @param year the value used to set the YEAR time field in the calendar.
     * @param month the value used to set the MONTH time field in the calendar.
     * Month value is 0-based. e.g., 0 for January.