/*
 * Copyright (c) 1996, 2018, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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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.Serializable;
import java.time.ZoneId;

import jdk.internal.util.StaticProperty;
import sun.security.action.GetPropertyAction;
import sun.util.calendar.ZoneInfo;
import sun.util.calendar.ZoneInfoFile;
import sun.util.locale.provider.TimeZoneNameUtility;

/**
 * <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 id="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 id="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".
 *
 * <h3>Three-letter time zone IDs</h3>
 *
 * 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 1.1
 */
public abstract 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;

 // 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 offsets 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.
 */
 public abstract 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;
 this.zoneId = null; // invalidate cache
 }

 /**
 * 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:
 * <blockquote><pre>
 * getDisplayName(false, {@link #LONG},
 * Locale.getDefault({@link Locale.Category#DISPLAY}))
 * </pre></blockquote>
 *
 * @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:
 * <blockquote><pre>
 * getDisplayName(false, {@link #LONG}, locale)
 * </pre></blockquote>
 *
 * @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:
 * <blockquote><pre>
 * getDisplayName(daylight, style,
 * Locale.getDefault({@link Locale.Category#DISPLAY}))
 * </pre></blockquote>
 *
 * @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 a name in the specified {@code style} of this {@code TimeZone}
 * suitable for presentation to the user in the specified {@code
 * 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>When looking up a time zone name, the {@linkplain
 * ResourceBundle.Control#getCandidateLocales(String,Locale) default
 * <code>Locale</code> search path of <code>ResourceBundle</code>} derived
 * from the specified {@code locale} is used. (No {@linkplain
 * ResourceBundle.Control#getFallbackLocale(String,Locale) fallback
 * <code>Locale</code>} search is performed.) If a time zone name in any
 * {@code Locale} of the search path, including {@link Locale#ROOT}, is
 * found, the name is returned. Otherwise, a string in the
 * <a href="#NormalizedCustomID">normalized custom ID format</a> is returned.
 *
 * @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}
 * @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 IllegalArgumentException if {@code style} is invalid.
 * @exception NullPointerException if {@code locale} is {@code null}.
 * @since 1.2
 * @see java.text.DateFormatSymbols#getZoneStrings()
 */
 public String getDisplayName(boolean daylight, int style, Locale locale) {
 if (style != SHORT && style != LONG) {
 throw new IllegalArgumentException("Illegal style: " + style);
 }
 String id = getID();
 String name = TimeZoneNameUtility.retrieveDisplayName(id, daylight, style, locale);
 if (name != null) {
 return name;
 }

 if (id.startsWith("GMT") && id.length() > 3) {
 char sign = id.charAt(3);
 if (sign == '+' || sign == '-') {
 return id;
 }
 }
 int offset = getRawOffset();
 if (daylight) {
 offset += getDSTSavings();
 }
 return ZoneInfoFile.toCustomID(offset);
 }

 private static String[] getDisplayNames(String id, Locale locale) {
 return TimeZoneNameUtility.retrieveDisplayNames(id, locale);
 }

 /**
 * 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.
 */
 public abstract 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) {
 return getTimeZone(ID, true);
 }

 /**
 * Gets the {@code TimeZone} for the given {@code zoneId}.
 *
 * @param zoneId a {@link ZoneId} from which the time zone ID is obtained
 * @return the specified {@code TimeZone}, or the GMT zone if the given ID
 * cannot be understood.
 * @throws NullPointerException if {@code zoneId} is {@code null}
 * @since 1.8
 */
 public static TimeZone getTimeZone(ZoneId zoneId) {
 String tzid = zoneId.getId(); // throws an NPE if null
 char c = tzid.charAt(0);
 if (c == '+' || c == '-') {
 tzid = "GMT" + tzid;
 } else if (c == 'Z' && tzid.length() == 1) {
 tzid = "UTC";
 }
 return getTimeZone(tzid, true);
 }

 /**
 * Converts this {@code TimeZone} object to a {@code ZoneId}.
 *
 * @return a {@code ZoneId} representing the same time zone as this
 * {@code TimeZone}
 * @since 1.8
 */
 public ZoneId toZoneId() {
 ZoneId zId = zoneId;
 if (zId == null) {
 zoneId = zId = toZoneId0();
 }
 return zId;
 }

 private ZoneId toZoneId0() {
 String id = getID();
 TimeZone defaultZone = defaultTimeZone;
 // are we not defaultTimeZone but our id is equal to default's?
 if (defaultZone != this &&
 defaultZone != null && id.equals(defaultZone.getID())) {
 // delegate to default TZ which is effectively immutable
 return defaultZone.toZoneId();
 }
 // derive it ourselves
 if (ZoneInfoFile.useOldMapping() && id.length() == 3) {
 if ("EST".equals(id))
 return ZoneId.of("America/New_York");
 if ("MST".equals(id))
 return ZoneId.of("America/Denver");
 if ("HST".equals(id))
 return ZoneId.of("America/Honolulu");
 }
 return ZoneId.of(id, ZoneId.SHORT_IDS);
 }

 private static TimeZone getTimeZone(String ID, boolean fallback) {
 TimeZone tz = ZoneInfo.getTimeZone(ID);
 if (tz == null) {
 tz = parseCustomTimeZone(ID);
 if (tz == null && fallback) {
 tz = new ZoneInfo(GMT_ID, 0);
 }
 }
 return tz;
 }

 /**
 * 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 ZoneInfo.getAvailableIDs(rawOffset);
 }

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

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

 /**
 * 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} of the Java virtual machine. If the
 * cached default {@code TimeZone} is available, its clone is returned.
 * Otherwise, the method takes the following steps to determine the default
 * time zone.
 *
 * <ul>
 * <li>Use the {@code user.timezone} property value as the default
 * time zone ID if it's available.</li>
 * <li>Detect the platform time zone ID. The source of the
 * platform time zone and ID mapping may vary with implementation.</li>
 * <li>Use {@code GMT} as the last resort if the given or detected
 * time zone ID is unknown.</li>
 * </ul>
 *
 * <p>The default {@code TimeZone} created from the ID is cached,
 * and its clone is returned. The {@code user.timezone} property
 * value is set to the ID upon return.
 *
 * @return the default {@code TimeZone}
 * @see #setDefault(TimeZone)
 */
 public static TimeZone getDefault() {
 return (TimeZone) getDefaultRef().clone();
 }

 /**
 * Returns the reference to the default TimeZone object. This
 * method doesn't create a clone.
 */
 static TimeZone getDefaultRef() {
 TimeZone defaultZone = defaultTimeZone;
 if (defaultZone == null) {
 // Need to initialize the default time zone.
 defaultZone = setDefaultZone();
 assert defaultZone != null;
 }
 // Don't clone here.
 return defaultZone;
 }

 private static synchronized TimeZone setDefaultZone() {
 TimeZone tz;
 // get the time zone ID from the system properties
 Properties props = GetPropertyAction.privilegedGetProperties();
 String zoneID = props.getProperty("user.timezone");

 // if the time zone ID is not set (yet), perform the
 // platform to Java time zone ID mapping.
 if (zoneID == null || zoneID.isEmpty()) {
 String javaHome = StaticProperty.javaHome();
 try {
 zoneID = getSystemTimeZoneID(javaHome);
 if (zoneID == null) {
 zoneID = GMT_ID;
 }
 } catch (NullPointerException e) {
 zoneID = GMT_ID;
 }
 }

 // Get the time zone for zoneID. But not fall back to
 // "GMT" here.
 tz = getTimeZone(zoneID, false);

 if (tz == null) {
 // If the given zone ID is unknown in Java, try to
 // get the GMT-offset-based time zone ID,
 // a.k.a. custom time zone ID (e.g., "GMT-08:00").
 String gmtOffsetID = getSystemGMTOffsetID();
 if (gmtOffsetID != null) {
 zoneID = gmtOffsetID;
 }
 tz = getTimeZone(zoneID, true);
 }
 assert tz != null;

 final String id = zoneID;
 props.setProperty("user.timezone", id);

 defaultTimeZone = tz;
 return tz;
 }

 /**
 * Sets the {@code TimeZone} that is returned by the {@code getDefault}
 * method. {@code zone} is cached. If {@code zone} is null, the cached
 * default {@code TimeZone} is cleared. This method doesn't change the value
 * of the {@code user.timezone} property.
 *
 * @param zone the new default {@code TimeZone}, or null
 * @throws SecurityException if the security manager's {@code checkPermission}
 * denies {@code PropertyPermission("user.timezone",
 * "write")}
 * @see #getDefault
 * @see PropertyPermission
 */
 public static void setDefault(TimeZone zone)
 {
 SecurityManager sm = System.getSecurityManager();
 if (sm != null) {
 sm.checkPermission(new PropertyPermission
 ("user.timezone", "write"));
 }
 // by saving a defensive clone and returning a clone in getDefault() too,
 // the defaultTimeZone instance is isolated from user code which makes it
 // effectively immutable. This is important to avoid races when the
 // following is evaluated in ZoneId.systemDefault():
 // TimeZone.getDefault().toZoneId().
 defaultTimeZone = (zone == null) ? null : (TimeZone) zone.clone();
 }

 /**
 * 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 {
 return super.clone();
 } catch (CloneNotSupportedException e) {
 throw new InternalError(e);
 }
 }

 /**
 * 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;

 /**
 * Cached {@link ZoneId} for this TimeZone
 */
 private transient ZoneId zoneId;

 private static volatile TimeZone defaultTimeZone;

 static final String GMT_ID = "GMT";
 private static final int GMT_ID_LENGTH = 3;

 /**
 * Parses a custom time zone identifier and returns a corresponding zone.
 * This method doesn't support the RFC 822 time zone format. (e.g., +hhmm)
 *
 * @param id a string of the <a href="#CustomID">custom ID form</a>.
 * @return a newly created TimeZone with the given offset and
 * no daylight saving time, or null if the id cannot be parsed.
 */
 private static final TimeZone parseCustomTimeZone(String id) {
 int length;

 // Error if the length of id isn't long enough or id doesn't
 // start with "GMT".
 if ((length = id.length()) < (GMT_ID_LENGTH + 2) ||
 id.indexOf(GMT_ID) != 0) {
 return null;
 }

 ZoneInfo zi;

 // First, we try to find it in the cache with the given
 // id. Even the id is not normalized, the returned ZoneInfo
 // should have its normalized id.
 zi = ZoneInfoFile.getZoneInfo(id);
 if (zi != null) {
 return zi;
 }

 int index = GMT_ID_LENGTH;
 boolean negative = false;
 char c = id.charAt(index++);
 if (c == '-') {
 negative = true;
 } else if (c != '+') {
 return null;
 }

 int hours = 0;
 int num = 0;
 int countDelim = 0;
 int len = 0;
 while (index < length) {
 c = id.charAt(index++);
 if (c == ':') {
 if (countDelim > 0) {
 return null;
 }
 if (len > 2) {
 return null;
 }
 hours = num;
 countDelim++;
 num = 0;
 len = 0;
 continue;
 }
 if (c < '0' || c > '9') {
 return null;
 }
 num = num * 10 + (c - '0');
 len++;
 }
 if (index != length) {
 return null;
 }
 if (countDelim == 0) {
 if (len <= 2) {
 hours = num;
 num = 0;
 } else {
 hours = num / 100;
 num %= 100;
 }
 } else {
 if (len != 2) {
 return null;
 }
 }
 if (hours > 23 || num > 59) {
 return null;
 }
 int gmtOffset = (hours * 60 + num) * 60 * 1000;

 if (gmtOffset == 0) {
 zi = ZoneInfoFile.getZoneInfo(GMT_ID);
 if (negative) {
 zi.setID("GMT-00:00");
 } else {
 zi.setID("GMT+00:00");
 }
 } else {
 zi = ZoneInfoFile.getCustomTimeZone(id, negative ? -gmtOffset : gmtOffset);
 }
 return zi;
 }
}