content: /*
   * Copyright (C) 2014 The Android Open Source Project
   * 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,
   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
   * or visit www.oracle.com if you need additional information or have any
   * questions.
   */
  
  /*
   * (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 android.icu.text.TimeZoneNames;
  import java.io.IOException;
  import java.io.Serializable;
  import java.time.ZoneId;
  import java.util.function.Supplier;
  import java.util.regex.Matcher;
  import java.util.regex.Pattern;
  import libcore.io.IoUtils;
  import libcore.timezone.ZoneInfoDb;
  
  import dalvik.system.RuntimeHooks;
  
  /**
   * <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".
   *
   * <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        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;
  
      // Android-changed: Use a preload holder to allow compile-time initialization of TimeZone and
      // dependents.
      private static class NoImagePreloadHolder {
          public 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;
  
      // Android-changed: common timezone instances.
      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 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.
       */
      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:
       * <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 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) {
          // BEGIN Android-changed: implement using android.icu.text.TimeZoneNames
          TimeZoneNames.NameType nameType;
          switch (style) {
              case SHORT:
                  nameType = daylightTime
                          ? TimeZoneNames.NameType.SHORT_DAYLIGHT
                          : TimeZoneNames.NameType.SHORT_STANDARD;
                  break;
              case LONG:
                  nameType = daylightTime
                          ? TimeZoneNames.NameType.LONG_DAYLIGHT
                          : TimeZoneNames.NameType.LONG_STANDARD;
                  break;
              default:
                  throw new IllegalArgumentException("Illegal style: " + style);
          }
          String canonicalID = android.icu.util.TimeZone.getCanonicalID(getID());
          if (canonicalID != null) {
              TimeZoneNames names = TimeZoneNames.getInstance(locale);
              long now = System.currentTimeMillis();
              String displayName = names.getDisplayName(canonicalID, nameType, now);
              if (displayName != null) {
                  return displayName;
              }
          }
  
          // We get here if this is a custom timezone or ICU doesn't have name data for the specific
          // style and locale.
          int offsetMillis = getRawOffset();
          if (daylightTime) {
              offsetMillis += getDSTSavings();
          }
          return createGmtOffsetString(true /* includeGmt */, true /* includeMinuteSeparator */,
                  offsetMillis);
          // END Android-changed: implement using android.icu.text.TimeZoneNames
      }
  
      // BEGIN Android-added: utility method to format an offset as a GMT offset string.
      /**
       * 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);
      }
      // END Android-added: utility method to format an offset as a GMT offset 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.
       */
      // Android-changed: param s/ID/id; use ZoneInfoDb instead of ZoneInfo class.
      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();
      }
  
      /**
       * 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);
      }
  
      /**
       * 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() {
          // Android-changed: don't support "old mapping"
          return ZoneId.of(getID(), ZoneId.SHORT_IDS);
      }
  
      /**
       * Returns a new SimpleTimeZone for an ID of the form "GMT[+|-]hh[[:]mm]", or null.
       */
      private static TimeZone getCustomTimeZone(String id) {
          Matcher m = NoImagePreloadHolder.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(Locale.ROOT, "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) {
              Supplier<String> tzGetter = RuntimeHooks.getTimeZoneIdSupplier();
              String zoneName = (tzGetter != null) ? tzGetter.get() : 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;
      }
  
      /**
       * Sets the {@code TimeZone} that is returned by the {@code getDefault}
       * method. {@code timeZone} is cached. If {@code timeZone} is null, the cached
       * default {@code TimeZone} is cleared. This method doesn't change the value
       * of the {@code user.timezone} property.
       *
       * @param timeZone the new default {@code TimeZone}, or null
       * @see #getDefault
       */
      // Android-changed: s/zone/timeZone, synchronized, removed mention of SecurityException
      public synchronized static void setDefault(TimeZone timeZone)
      {
          SecurityManager sm = System.getSecurityManager();
          if (sm != null) {
              sm.checkPermission(new PropertyPermission
                      ("user.timezone", "write"));
          }
          defaultTimeZone = timeZone != null ? (TimeZone) timeZone.clone() : null;
          // Android-changed: notify ICU4J of changed default TimeZone.
          android.icu.util.TimeZone.setICUDefault(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(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;
      private static volatile TimeZone defaultTimeZone;
  }
  