timezone.java

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/*
 * @(#)TimeZone.java	1.63 03/01/23
 *
 * Copyright 2003 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

/*
 * (C) Copyright Taligent, Inc. 1996 - All Rights Reserved
 * (C) Copyright IBM Corp. 1996 - 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.
 *
 */

package java.util;
import java.io.Serializable;
import java.lang.ref.SoftReference;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.text.SimpleDateFormat;
import sun.security.action.GetPropertyAction;
import sun.util.calendar.ZoneInfo;
import sun.util.calendar.ZoneInfoFile;

/**
 * <code>TimeZone</code> represents a time zone offset, and also figures out daylight
 * savings.
 *
 * <p>
 * Typically, you get a <code>TimeZone</code> using <code>getDefault</code>
 * which creates a <code>TimeZone</code> based on the time zone where the program
 * is running. For example, for a program running in Japan, <code>getDefault</code>
 * creates a <code>TimeZone</code> object based on Japanese Standard Time.
 *
 * <p>
 * You can also get a <code>TimeZone</code> using <code>getTimeZone</code>
 * along with a time zone ID. For instance, the time zone ID for the
 * U.S. Pacific Time zone is "America/Los_Angeles". So, you can get a
 * U.S. Pacific Time <code>TimeZone</code> object with:
 * <blockquote><pre>
 * TimeZone tz = TimeZone.getTimeZone("America/Los_Angeles");
 * </pre></blockquote>
 * You can use the <code>getAvailableIDs</code> method to iterate through
 * all the supported time zone IDs. You can then choose a
 * supported ID to get a <code>TimeZone</code>.
 * If the time zone you want is not represented by one of the
 * supported IDs, then a custom time zone ID can be specified to
 * produce a TimeZone. The syntax of a custom time zone ID is:
 *
 * <blockquote><pre>
 * <a name="CustomID"><i>CustomID:</i></a>
 *         <code>GMT</code> <i>Sign</i> <i>Hours</i> <code>:</code> <i>Minutes</i>
 *         <code>GMT</code> <i>Sign</i> <i>Hours</i> <i>Minutes</i>
 *         <code>GMT</code> <i>Sign</i> <i>Hours</i>
 * <i>Sign:</i> one of
 *         <code>+ -</code>
 * <i>Hours:</i>
 *         <i>Digit</i>
 *         <i>Digit</i> <i>Digit</i>
 * <i>Minutes:</i>
 *         <i>Digit</i> <i>Digit</i>
 * <i>Digit:</i> one of
 *         <code>0 1 2 3 4 5 6 7 8 9</code>
 * </pre></blockquote>
 *
 * <i>Hours</i> must be between 0 to 23 and <i>Minutes</i> must be
 * between 00 to 59.  For example, "GMT+10" and "GMT+0010" mean ten
 * hours and ten minutes ahead of GMT, respectively.
 * <p>
 * The format is locale independent and digits must be taken from the
 * Basic Latin block of the Unicode standard. No daylight saving time
 * transition schedule can be specified with a custom time zone ID. If
 * the specified string doesn't match the syntax, <code>"GMT"</code>
 * is used.
 * <p>
 * When creating a <code>TimeZone</code>, the specified custom time
 * zone ID is normalized in the following syntax:
 * <blockquote><pre>
 * <a name="NormalizedCustomID"><i>NormalizedCustomID:</i></a>
 *         <code>GMT</code> <i>Sign</i> <i>TwoDigitHours</i> <code>:</code> <i>Minutes</i>
 * <i>Sign:</i> one of
 *         <code>+ -</code>
 * <i>TwoDigitHours:</i>
 *         <i>Digit</i> <i>Digit</i>
 * <i>Minutes:</i>
 *         <i>Digit</i> <i>Digit</i>
 * <i>Digit:</i> one of
 *         <code>0 1 2 3 4 5 6 7 8 9</code>
 * </pre></blockquote>
 * For example, TimeZone.getTimeZone("GMT-8").getID() returns "GMT-08:00".
 *
 * <h4>Three-letter time zone IDs</h4>
 * 
 * For compatibility with JDK 1.1.x, some other three-letter time zone IDs
 * (such as "PST", "CTT", "AST") are also supported. However, <strong>their
 * use is deprecated</strong> because the same abbreviation is often used
 * for multiple time zones (for example, "CST" could be U.S. "Central Standard
 * Time" and "China Standard Time"), and the Java platform can then only
 * recognize one of them.
 *
 *
 * @see          Calendar
 * @see          GregorianCalendar
 * @see          SimpleTimeZone
 * @version      1.63 01/23/03
 * @author       Mark Davis, David Goldsmith, Chen-Lieh Huang, Alan Liu
 * @since        JDK1.1
 */
abstract public class TimeZone implements Serializable, Cloneable {
    /**
     * Sole constructor.  (For invocation by subclass constructors, typically
     * implicit.)
     */
    public TimeZone() {
    }

    /**
     * A style specifier for <code>getDisplayName()</code> indicating
     * a short name, such as "PST."
     * @see #LONG
     * @since 1.2
     */
    public static final int SHORT = 0;

    /**
     * A style specifier for <code>getDisplayName()</code> indicating
     * a long name, such as "Pacific Standard Time."
     * @see #SHORT
     * @since 1.2
     */
    public static final int LONG  = 1;

    // Constants used internally; unit is milliseconds
    private static final int ONE_MINUTE = 60*1000;
    private static final int ONE_HOUR   = 60*ONE_MINUTE;
    private static final int ONE_DAY    = 24*ONE_HOUR;

    /**
     * Cache to hold the SimpleDateFormat objects for a Locale.
     */
    private static Hashtable cachedLocaleData = new Hashtable(3);

    // Proclaim serialization compatibility with JDK 1.1
    static final long serialVersionUID = 3581463369166924961L;

    /**
     * Gets the time zone offset, for current date, modified in case of
     * daylight savings. This is the offset to add to UTC to get local time.
     * <p>
     * This method returns a historically correct offset if an
     * underlying <code>TimeZone</code> implementation subclass
     * supports historical Daylight Saving Time schedule and GMT
     * offset changes.
     *
     * @param era the era of the given date.
     * @param year the year in the given date.
     * @param month the month in the given date.
     * Month is 0-based. e.g., 0 for January.
     * @param day the day-in-month of the given date.
     * @param dayOfWeek the day-of-week of the given date.
     * @param milliseconds the milliseconds in day in <em>standard</em>
     * local time.
     *
     * @return the offset in milliseconds to add to GMT to get local time.
     *
     * @see Calendar#ZONE_OFFSET
     * @see Calendar#DST_OFFSET
     */
    public abstract int getOffset(int era, int year, int month, int day,
                                  int dayOfWeek, int milliseconds);

    /**
     * Returns the offset of this time zone from UTC at the specified
     * date. If Daylight Saving Time is in effect at the specified
     * date, the offset value is adjusted with the amount of daylight
     * saving.
     * <p>
     * This method returns a historically correct offset value if an
     * underlying TimeZone implementation subclass supports historical
     * Daylight Saving Time schedule and GMT offset changes.
     *
     * @param date the date represented in milliseconds since January 1, 1970 00:00:00 GMT
     * @return the amount of time in milliseconds to add to UTC to get local time.
     *
     * @see Calendar#ZONE_OFFSET
     * @see Calendar#DST_OFFSET
     * @since 1.4
     */
    public int getOffset(long date) {
	if (inDaylightTime(new Date(date))) {
	    return getRawOffset() + getDSTSavings();
	}
	return getRawOffset();
    }

    /**
     * Gets the raw GMT offset and the amount of daylight saving of this
     * time zone at the given time.
     * @param date the milliseconds (since January 1, 1970,
     * 00:00:00.000 GMT) at which the time zone offset and daylight
     * saving amount are found
     * @param offset an array of int where the raw GMT offset
     * (offset[0]) and daylight saving amount (offset[1]) are stored,
     * or null if those values are not needed. The method assumes that
     * the length of the given array is two or larger.
     * @return the total amount of the raw GMT offset and daylight
     * saving at the specified date.
     *
     * @see Calendar#ZONE_OFFSET
     * @see Calendar#DST_OFFSET
     */
    int getOffsets(long date, int[] offsets) {
	int rawoffset = getRawOffset();
	int dstoffset = 0;
	if (inDaylightTime(new Date(date))) {
	    dstoffset = getDSTSavings();
	}
	if (offsets != null) {
	    offsets[0] = rawoffset;
	    offsets[1] = dstoffset;
	}
	return rawoffset + dstoffset;
    }

    /**
     * Sets the base time zone offset to GMT.
     * This is the offset to add to UTC to get local time.
     * <p>
     * If an underlying <code>TimeZone</code> implementation subclass
     * supports historical GMT offset changes, the specified GMT
     * offset is set as the latest GMT offset and the difference from
     * the known latest GMT offset value is used to adjust all
     * historical GMT offset values.
     *
     * @param offsetMillis the given base time zone offset to GMT.
     */
    abstract public void setRawOffset(int offsetMillis);

    /**
     * Returns the amount of time in milliseconds to add to UTC to get
     * standard time in this time zone. Because this value is not
     * affected by daylight saving time, it is called <I>raw
     * offset</I>.
     * <p>
     * If an underlying <code>TimeZone</code> implementation subclass
     * supports historical GMT offset changes, the method returns the
     * raw offset value of the current date. In Honolulu, for example,
     * its raw offset changed from GMT-10:30 to GMT-10:00 in 1947, and
     * this method always returns -36000000 milliseconds (i.e., -10
     * hours).
     *
     * @return the amount of raw offset time in milliseconds to add to UTC.
     * @see Calendar#ZONE_OFFSET
     */
    public abstract int getRawOffset();

    /**
     * Gets the ID of this time zone.
     * @return the ID of this time zone.
     */
    public String getID()
    {
        return ID;
    }

    /**
     * Sets the time zone ID. This does not change any other data in
     * the time zone object.
     * @param ID the new time zone ID.
     */
    public void setID(String ID)
    {
        if (ID == null) {
            throw new NullPointerException();
        }
        this.ID = ID;
    }

    /**
     * Returns a name of this time zone suitable for presentation to the user
     * in the default locale.
     * This method returns the long name, not including daylight savings.
     * If the display name is not available for the locale,
     * then this method returns a string in the 
     * <a href="#NormalizedCustomID">normalized custom ID format</a>.
     * @return the human-readable name of this time zone in the default locale.
     * @since 1.2
     */
    public final String getDisplayName() {
        return getDisplayName(false, LONG, Locale.getDefault());
    }

    /**
     * Returns a name of this time zone suitable for presentation to the user
     * in the specified locale.
     * This method returns the long name, not including daylight savings.
     * If the display name is not available for the locale,
     * then this method returns a string in the 
     * <a href="#NormalizedCustomID">normalized custom ID format</a>.
     * @param locale the locale in which to supply the display name.
     * @return the human-readable name of this time zone in the given locale
     * or in the default locale if the given locale is not recognized.
     * @since 1.2
     */
    public final String getDisplayName(Locale locale) {
        return getDisplayName(false, LONG, locale);
    }

    /**
     * Returns a name of this time zone suitable for presentation to the user
     * in the default locale.
     * If the display name is not available for the locale, then this
     * method returns a string in the 
     * <a href="#NormalizedCustomID">normalized custom ID format</a>.
     * @param daylight if true, return the daylight savings name.
     * @param style either <code>LONG</code> or <code>SHORT</code>
     * @return the human-readable name of this time zone in the default locale.
     * @since 1.2
     */
    public final String getDisplayName(boolean daylight, int style) {
        return getDisplayName(daylight, style, Locale.getDefault());
    }

    /**
     * Returns a name of this time zone suitable for presentation to the user
     * in the specified locale.
     * If the display name is not available for the locale,
     * then this method returns a string in the 
     * <a href="#NormalizedCustomID">normalized custom ID format</a>.
     * @param daylight if true, return the daylight savings name.
     * @param style either <code>LONG</code> or <code>SHORT</code>
     * @param locale the locale in which to supply the display name.
     * @return the human-readable name of this time zone in the given locale
     * or in the default locale if the given locale is not recognized.
     * @exception IllegalArgumentException style is invalid.
     * @since 1.2
     */
    public String getDisplayName(boolean daylight, int style, Locale locale) {
        /* NOTES:
         * (1) We use SimpleDateFormat for simplicity; we could do this
         * more efficiently but it would duplicate the SimpleDateFormat code
         * here, which is undesirable.
         * (2) Attempts to move the code from SimpleDateFormat to here also run
         * around because this requires SimpleDateFormat to keep a Locale
         * object around, which it currently doesn't; to synthesize such a
         * locale upon resurrection; and to somehow handle the special case of
         * construction from a DateFormatSymbols object.