java/util/TimeZone.java

/*
 * Copyright (c) 1996, 2013, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code 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 General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
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 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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/*
 * (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.IOException;
import java.io.Serializable;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import java.lang.ref.SoftReference;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.concurrent.ConcurrentHashMap;
import libcore.icu.TimeZoneNames;
import libcore.io.IoUtils;
import libcore.util.ZoneInfoDB;
import sun.security.action.GetPropertyAction;
import org.apache.harmony.luni.internal.util.TimezoneGetter;

/**
 * <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
 * @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;

    private static final Pattern CUSTOM_ZONE_ID_PATTERN = Pattern.compile("^GMT[-+](\\d{1,2})(:?(\\d\\d))?$");

    // Proclaim serialization compatibility with JDK 1.1
    static final long serialVersionUID = 3581463369166924961L;
    private static final TimeZone GMT = new SimpleTimeZone(0, "GMT");
    private static final TimeZone UTC = new SimpleTimeZone(0, "UTC");

    /**
     * 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 long standard time name of this {@code TimeZone} suitable for
     * presentation to the user in the default locale.
     *
     * <p>This method is equivalent to:
     * <pre><blockquote>
     * getDisplayName(false, {@link #LONG},
     *                Locale.getDefault({@link Locale.Category#DISPLAY}))
     * </blockquote></pre>
     *
     * @return the human-readable name of this time zone in the default locale.
     * @since 1.2
     * @see #getDisplayName(boolean, int, Locale)
     * @see Locale#getDefault(Locale.Category)
     * @see Locale.Category
     */
    public final String getDisplayName() {
        return getDisplayName(false, LONG,
                              Locale.getDefault(Locale.Category.DISPLAY));
    }

    /**
     * Returns a long standard time name of this {@code TimeZone} suitable for
     * presentation to the user in the specified {@code locale}.
     *
     * <p>This method is equivalent to:
     * <pre><blockquote>
     * getDisplayName(false, {@link #LONG}, locale)
     * </blockquote></pre>
     *
     * @param locale the locale in which to supply the display name.
     * @return the human-readable name of this time zone in the given locale.
     * @exception NullPointerException if {@code locale} is {@code null}.
     * @since 1.2
     * @see #getDisplayName(boolean, int, Locale)
     */
    public final String getDisplayName(Locale locale) {
        return getDisplayName(false, LONG, locale);
    }

    /**
     * Returns a name in the specified {@code style} of this {@code TimeZone}
     * suitable for presentation to the user in the default locale. If the
     * specified {@code daylight} is {@code true}, a Daylight Saving Time name
     * is returned (even if this {@code TimeZone} doesn't observe Daylight Saving
     * Time). Otherwise, a Standard Time name is returned.
     *
     * <p>This method is equivalent to:
     * <pre><blockquote>
     * getDisplayName(daylight, style,
     *                Locale.getDefault({@link Locale.Category#DISPLAY}))
     * </blockquote></pre>
     *
     * @param daylight {@code true} specifying a Daylight Saving Time name, or
     *                 {@code false} specifying a Standard Time name
     * @param style either {@link #LONG} or {@link #SHORT}
     * @return the human-readable name of this time zone in the default locale.
     * @exception IllegalArgumentException if {@code style} is invalid.
     * @since 1.2
     * @see #getDisplayName(boolean, int, Locale)
     * @see Locale#getDefault(Locale.Category)
     * @see Locale.Category
     * @see java.text.DateFormatSymbols#getZoneStrings()
     */
    public final String getDisplayName(boolean daylight, int style) {
        return getDisplayName(daylight, style,
                              Locale.getDefault(Locale.Category.DISPLAY));
    }

    /**
     * Returns the {@link #SHORT short} or {@link #LONG long} name of this time
     * zone with either standard or daylight time, as written in {@code locale}.
     * If the name is not available, the result is in the format
     * {@code GMT[+-]hh:mm}.
     *
     * @param daylightTime true for daylight time, false for standard time.
     * @param style either {@link TimeZone#LONG} or {@link TimeZone#SHORT}.
     * @param locale the display locale.
     */
    public String getDisplayName(boolean daylightTime, int style, Locale locale) {
        if (style != SHORT && style != LONG) {
            throw new IllegalArgumentException("Bad style: " + style);
        }

        String[][] zoneStrings = TimeZoneNames.getZoneStrings(locale);
        String result = TimeZoneNames.getDisplayName(zoneStrings, getID(), daylightTime, style);
        if (result != null) {
            return result;
        }

        // If we get here, it's because icu4c has nothing for us. Most commonly, this is in the
        // case of short names. For Pacific/Fiji, for example, icu4c has nothing better to offer
        // than "GMT+12:00". Why do we re-do this work ourselves? Because we have up-to-date
        // time zone transition data, which icu4c _doesn't_ use --- it uses its own baked-in copy,
        // which only gets updated when we update icu4c. http://b/7955614 and http://b/8026776.

        // TODO: should we generate these once, in TimeZoneNames.getDisplayName? Revisit when we
        // upgrade to icu4c 50 and rewrite the underlying native code. See also the
        // "element[j] != null" check in SimpleDateFormat.parseTimeZone, and the extra work in
        // DateFormatSymbols.getZoneStrings.
        int offsetMillis = getRawOffset();
        if (daylightTime) {
            offsetMillis += getDSTSavings();
        }
        return createGmtOffsetString(true /* includeGmt */, true /* includeMinuteSeparator */,
                offsetMillis);
    }

    /**
     * Returns a string representation of an offset from UTC.
     *
     * <p>The format is "[GMT](+|-)HH[:]MM". The output is not localized.
     *
     * @param includeGmt true to include "GMT", false to exclude
     * @param includeMinuteSeparator true to include the separator between hours and minutes, false
     *     to exclude.
     * @param offsetMillis the offset from UTC
     *
     * @hide used internally by SimpleDateFormat
     */
    public static String createGmtOffsetString(boolean includeGmt,
            boolean includeMinuteSeparator, int offsetMillis) {
        int offsetMinutes = offsetMillis / 60000;
        char sign = '+';
        if (offsetMinutes < 0) {
            sign = '-';
            offsetMinutes = -offsetMinutes;
        }
        StringBuilder builder = new StringBuilder(9);
        if (includeGmt) {
            builder.append("GMT");
        }
        builder.append(sign);
        appendNumber(builder, 2, offsetMinutes / 60);
        if (includeMinuteSeparator) {
            builder.append(':');
        }
        appendNumber(builder, 2, offsetMinutes % 60);
        return builder.toString();
    }

    private static void appendNumber(StringBuilder builder, int count, int value) {
        String string = Integer.toString(value);
        for (int i = 0; i < count - string.length(); i++) {
            builder.append('0');
        }
        builder.append(string);
    }

    /**
     * Returns the amount of time to be added to local standard time
     * to get local wall clock time.
     *
     * <p>The default implementation returns 3600000 milliseconds
     * (i.e., one hour) if a call to {@link #useDaylightTime()}
     * returns {@code true}. Otherwise, 0 (zero) is returned.
     *
     * <p>If an underlying {@code TimeZone} implementation subclass
     * supports historical and future Daylight Saving Time schedule
     * changes, this method returns the amount of saving time of the
     * last known Daylight Saving Time rule that can be a future
     * prediction.
     *
     * <p>If the amount of saving time at any given time stamp is
     * required, construct a {@link Calendar} with this {@code
     * TimeZone} and the time stamp, and call {@link Calendar#get(int)
     * Calendar.get}{@code (}{@link Calendar#DST_OFFSET}{@code )}.
     *
     * @return the amount of saving time in milliseconds
     * @since 1.4
     * @see #inDaylightTime(Date)
     * @see #getOffset(long)
     * @see #getOffset(int,int,int,int,int,int)
     * @see Calendar#ZONE_OFFSET
     */
    public int getDSTSavings() {
        if (useDaylightTime()) {
            return 3600000;
        }
        return 0;
    }

    /**
     * Queries if this {@code TimeZone} uses Daylight Saving Time.
     *
     * <p>If an underlying {@code TimeZone} implementation subclass
     * supports historical and future Daylight Saving Time schedule
     * changes, this method refers to the last known Daylight Saving Time
     * rule that can be a future prediction and may not be the same as
     * the current rule. Consider calling {@link #observesDaylightTime()}
     * if the current rule should also be taken into account.
     *
     * @return {@code true} if this {@code TimeZone} uses Daylight Saving Time,
     *         {@code false}, otherwise.
     * @see #inDaylightTime(Date)
     * @see Calendar#DST_OFFSET
     */
    public abstract boolean useDaylightTime();

    /**
     * Returns {@code true} if this {@code TimeZone} is currently in
     * Daylight Saving Time, or if a transition from Standard Time to
     * Daylight Saving Time occurs at any future time.
     *
     * <p>The default implementation returns {@code true} if
     * {@code useDaylightTime()} or {@code inDaylightTime(new Date())}
     * returns {@code true}.
     *
     * @return {@code true} if this {@code TimeZone} is currently in
     * Daylight Saving Time, or if a transition from Standard Time to
     * Daylight Saving Time occurs at any future time; {@code false}
     * otherwise.
     * @since 1.7
     * @see #useDaylightTime()
     * @see #inDaylightTime(Date)
     * @see Calendar#DST_OFFSET
     */
    public boolean observesDaylightTime() {
        return useDaylightTime() || inDaylightTime(new Date());
    }

    /**
     * Queries if the given {@code date} is in Daylight Saving Time in
     * this time zone.
     *
     * @param date the given Date.
     * @return {@code true} if the given date is in Daylight Saving Time,
     *         {@code false}, otherwise.
     */
    abstract public boolean inDaylightTime(Date date);

    /**
     * Gets the <code>TimeZone</code> for the given ID.
     *
     * @param ID the ID for a <code>TimeZone</code>, either an abbreviation
     * such as "PST", a full name such as "America/Los_Angeles", or a custom
     * ID such as "GMT-8:00". Note that the support of abbreviations is
     * for JDK 1.1.x compatibility only and full names should be used.
     *
     * @return the specified <code>TimeZone</code>, or the GMT zone if the given ID
     * cannot be understood.
     */
    public static synchronized TimeZone getTimeZone(String id) {
        if (id == null) {
            throw new NullPointerException("id == null");
        }

        // Special cases? These can clone an existing instance.
        if (id.length() == 3) {
            if (id.equals("GMT")) {
                return (TimeZone) GMT.clone();
            }
            if (id.equals("UTC")) {
                return (TimeZone) UTC.clone();
            }
        }

        // In the database?
        TimeZone zone = null;
        try {
            zone = ZoneInfoDB.getInstance().makeTimeZone(id);
        } catch (IOException ignored) {
        }

        // Custom time zone?
        if (zone == null && id.length() > 3 && id.startsWith("GMT")) {
            zone = getCustomTimeZone(id);
        }

        // We never return null; on failure we return the equivalent of "GMT".
        return (zone != null) ? zone : (TimeZone) GMT.clone();
    }

    /**
     * Returns a new SimpleTimeZone for an ID of the form "GMT[+|-]hh[[:]mm]", or null.
     */
    private static TimeZone getCustomTimeZone(String id) {
        Matcher m = CUSTOM_ZONE_ID_PATTERN.matcher(id);
        if (!m.matches()) {
            return null;
        }

        int hour;
        int minute = 0;
        try {
            hour = Integer.parseInt(m.group(1));
            if (m.group(3) != null) {
                minute = Integer.parseInt(m.group(3));
            }
        } catch (NumberFormatException impossible) {
            throw new AssertionError(impossible);
        }

        if (hour < 0 || hour > 23 || minute < 0 || minute > 59) {
            return null;
        }

        char sign = id.charAt(3);
        int raw = (hour * 3600000) + (minute * 60000);
        if (sign == '-') {
            raw = -raw;
        }

        String cleanId = String.format("GMT%c%02d:%02d", sign, hour, minute);
        return new SimpleTimeZone(raw, cleanId);
    }

    /**
     * Gets the available IDs according to the given time zone offset in milliseconds.
     *
     * @param rawOffset the given time zone GMT offset in milliseconds.
     * @return an array of IDs, where the time zone for that ID has
     * the specified GMT offset. For example, "America/Phoenix" and "America/Denver"
     * both have GMT-07:00, but differ in daylight saving behavior.
     * @see #getRawOffset()
     */
    public static synchronized String[] getAvailableIDs(int rawOffset) {
        return ZoneInfoDB.getInstance().getAvailableIDs(rawOffset);
    }

    /**
     * Gets all the available IDs supported.
     * @return an array of IDs.
     */
    public static synchronized String[] getAvailableIDs() {
        return ZoneInfoDB.getInstance().getAvailableIDs();
    }

    /**
     * Gets the platform defined TimeZone ID.
     **/
    private static native String getSystemTimeZoneID(String javaHome,
                                                     String country);

    /**
     * Gets the custom time zone ID based on the GMT offset of the
     * platform. (e.g., "GMT+08:00")
     */
    private static native String getSystemGMTOffsetID();

    /**
     * Gets the default <code>TimeZone</code> for this host.
     * The source of the default <code>TimeZone</code>
     * may vary with implementation.
     * @return a default <code>TimeZone</code>.
     * @see #setDefault
     */
    public static TimeZone getDefault() {
        return (TimeZone) getDefaultRef().clone();
    }

    /**
     * Returns the reference to the default TimeZone object. This
     * method doesn't create a clone.
     */
    static synchronized TimeZone getDefaultRef() {
        if (defaultTimeZone == null) {
            TimezoneGetter tzGetter = TimezoneGetter.getInstance();
            String zoneName = (tzGetter != null) ? tzGetter.getId() : null;
            if (zoneName != null) {
                zoneName = zoneName.trim();
            }
            if (zoneName == null || zoneName.isEmpty()) {
                try {
                    // On the host, we can find the configured timezone here.
                    zoneName = IoUtils.readFileAsString("/etc/timezone");
                } catch (IOException ex) {
                    // "vogar --mode device" can end up here.
                    // TODO: give libcore access to Android system properties and read "persist.sys.timezone".
                    zoneName = "GMT";
                }
            }
            defaultTimeZone = TimeZone.getTimeZone(zoneName);
        }
        return defaultTimeZone;
    }

    private static boolean hasPermission() {
        boolean hasPermission = true;
        SecurityManager sm = System.getSecurityManager();
        if (sm != null) {
            try {
                sm.checkPermission(new PropertyPermission
                                   ("user.timezone", "write"));
            } catch (SecurityException e) {
                hasPermission = false;
            }
        }
        return hasPermission;
    }

    /**
     * Sets the <code>TimeZone</code> that is
     * returned by the <code>getDefault</code> method.  If <code>zone</code>
     * is null, reset the default to the value it had originally when the
     * VM first started.
     * @param zone the new default time zone
     * @see #getDefault
     */
    public synchronized static void setDefault(TimeZone timeZone)
    {
        if (hasPermission()) {
            defaultTimeZone = timeZone != null ? (TimeZone) timeZone.clone() : null;
        }
    }

    /**
     * Returns true if this zone has the same rule and offset as another zone.
     * That is, if this zone differs only in ID, if at all.  Returns false
     * if the other zone is null.
     * @param other the <code>TimeZone</code> object to be compared with
     * @return true if the other zone is not null and is the same as this one,
     * with the possible exception of the ID
     * @since 1.2
     */
    public boolean hasSameRules(TimeZone other) {
        return other != null && getRawOffset() == other.getRawOffset() &&
            useDaylightTime() == other.useDaylightTime();
    }

    /**
     * Creates a copy of this <code>TimeZone</code>.
     *
     * @return a clone of this <code>TimeZone</code>
     */
    public Object clone()
    {
        try {
            TimeZone other = (TimeZone) super.clone();
            other.ID = ID;
            return other;
        } catch (CloneNotSupportedException e) {
            throw new InternalError();
        }
    }

    /**
     * The null constant as a TimeZone.
     */
    static final TimeZone NO_TIMEZONE = null;

    // =======================privates===============================

    /**
     * The string identifier of this <code>TimeZone</code>.  This is a
     * programmatic identifier used internally to look up <code>TimeZone</code>
     * objects from the system table and also to map them to their localized
     * display names.  <code>ID</code> values are unique in the system
     * table but may not be for dynamically created zones.
     * @serial
     */
    private String           ID;
    private static volatile TimeZone defaultTimeZone;
}