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Android Reference

TimeZone


java.util

Class TimeZone

  • All Implemented Interfaces:
    Serializable, Cloneable
    Direct Known Subclasses:
    SimpleTimeZone


    public abstract class TimeZone
    extends Object
    implements Serializable, Cloneable
    TimeZone represents a time zone, primarily used for configuring a Calendar or SimpleDateFormat instance.

    Most applications will use getDefault() which returns a TimeZone based on the time zone where the program is running.

    You can also get a specific TimeZone by Olson ID.

    It is highly unlikely you'll ever want to use anything but the factory methods yourself. Let classes like Calendar and SimpleDateFormat do the date computations for you.

    If you do need to do date computations manually, there are two common cases to take into account:

    • Somewhere like California, where daylight time is used. The useDaylightTime() method will always return true, and inDaylightTime(java.util.Date) must be used to determine whether or not daylight time applies to a given Date. The getRawOffset() method will return a raw offset of (in this case) -8 hours from UTC, which isn't usually very useful. More usefully, the getOffset(long) methods return the actual offset from UTC for a given point in time; this is the raw offset plus (if the point in time is in daylight time) the applicable DST savings (usually, but not necessarily, 1 hour).
    • Somewhere like Japan, where daylight time is not used. The useDaylightTime() and inDaylightTime(java.util.Date) methods both always return false, and the raw and actual offsets will always be the same.

    Note the type returned by the factory methods getDefault() and getTimeZone(java.lang.String) is implementation dependent. This may introduce serialization incompatibility issues between different implementations. Android returns instances of SimpleTimeZone so that the bytes serialized by Android can be deserialized successfully on other implementations, but the reverse compatibility cannot be guaranteed.

    See Also:
    Calendar, GregorianCalendar, SimpleDateFormat, SimpleTimeZone, Serialized Form
    • Field Summary

      Fields
      Modifier and Type Field and Description
      static int LONG
      The long display name style, such as Pacific Daylight Time.
      static int SHORT
      The short display name style, such as PDT.
    • Constructor Summary

      Constructors
      Constructor and Description
      TimeZone()
    • Method Summary

      Methods
      Modifier and Type Method and Description
      Object clone()
      Returns a new time zone with the same ID, raw offset, and daylight savings time rules as this time zone.
      static String[] getAvailableIDs()
      Returns the system's installed time zone IDs.
      static String[] getAvailableIDs(int offsetMillis)
      Returns the IDs of the time zones whose offset from UTC is offsetMillis.
      static TimeZone getDefault()
      Returns the user's preferred time zone.
      String getDisplayName()
      Equivalent to getDisplayName(false, TimeZone.LONG, Locale.getDefault()).
      String getDisplayName(boolean daylightTime, int style)
      Equivalent to getDisplayName(daylightTime, style, Locale.getDefault()).
      String getDisplayName(boolean daylightTime, int style, Locale locale)
      Returns the short or long name of this time zone with either standard or daylight time, as written in locale.
      String getDisplayName(Locale locale)
      Equivalent to getDisplayName(false, TimeZone.LONG, locale).
      int getDSTSavings()
      Returns the latest daylight savings in milliseconds for this time zone, relative to this time zone's regular UTC offset (as returned by getRawOffset()).
      String getID()
      Returns the ID of this TimeZone, such as America/Los_Angeles, GMT-08:00 or UTC.
      abstract int getOffset(int era, int year, int month, int day, int dayOfWeek, int timeOfDayMillis)
      Returns this time zone's offset in milliseconds from UTC at the specified date and time.
      int getOffset(long time)
      Returns the offset in milliseconds from UTC for this time zone at time.
      abstract int getRawOffset()
      Returns the offset in milliseconds from UTC of this time zone's standard time.
      static TimeZone getTimeZone(String id)
      Returns a TimeZone corresponding to the given id, or GMT for unknown ids.
      boolean hasSameRules(TimeZone timeZone)
      Returns true if timeZone has the same rules as this time zone.
      abstract boolean inDaylightTime(Date time)
      Returns true if time is in a daylight savings time period for this time zone.
      static void setDefault(TimeZone timeZone)
      Overrides the default time zone for the current process only.
      void setID(String id)
      Sets the ID of this TimeZone.
      abstract void setRawOffset(int offsetMillis)
      Sets the offset in milliseconds from UTC of this time zone's standard time.
      abstract boolean useDaylightTime()
      Returns true if this time zone has a future transition to or from daylight savings time.
    • Field Detail

      • SHORT

        public static final int SHORT
        The short display name style, such as PDT. Requests for this style may yield GMT offsets like GMT-08:00.
        See Also:
        Constant Field Values
      • LONG

        public static final int LONG
        The long display name style, such as Pacific Daylight Time. Requests for this style may yield GMT offsets like GMT-08:00.
        See Also:
        Constant Field Values
    • Constructor Detail

      • TimeZone

        public TimeZone()
    • Method Detail

      • clone

        public Object clone()
        Returns a new time zone with the same ID, raw offset, and daylight savings time rules as this time zone.
        Overrides:
        clone in class Object
        Returns:
        a copy of this object.
      • getAvailableIDs

        public static String[] getAvailableIDs()
        Returns the system's installed time zone IDs. Any of these IDs can be passed to getTimeZone(java.lang.String) to lookup the corresponding time zone instance.
      • getAvailableIDs

        public static String[] getAvailableIDs(int offsetMillis)
        Returns the IDs of the time zones whose offset from UTC is offsetMillis. Any of these IDs can be passed to getTimeZone(java.lang.String) to lookup the corresponding time zone instance.
        Returns:
        a possibly-empty array.
      • getDefault

        public static TimeZone getDefault()
        Returns the user's preferred time zone. This may have been overridden for this process with setDefault(java.util.TimeZone).

        Since the user's time zone changes dynamically, avoid caching this value. Instead, use this method to look it up for each use.

      • getDisplayName

        public final String getDisplayName(Locale locale)
        Equivalent to getDisplayName(false, TimeZone.LONG, locale).
      • getDisplayName

        public final String getDisplayName(boolean daylightTime,
                            int style)
        Equivalent to getDisplayName(daylightTime, style, Locale.getDefault()). Be wary of the default locale.
      • getDisplayName

        public String getDisplayName(boolean daylightTime,
                            int style,
                            Locale locale)
        Returns the short or long name of this time zone with either standard or daylight time, as written in locale. If the name is not available, the result is in the format GMT[+-]hh:mm.
        Parameters:
        daylightTime - true for daylight time, false for standard time.
        style - either LONG or SHORT.
        locale - the display locale.
      • getID

        public String getID()
        Returns the ID of this TimeZone, such as America/Los_Angeles, GMT-08:00 or UTC.
      • getDSTSavings

        public int getDSTSavings()
        Returns the latest daylight savings in milliseconds for this time zone, relative to this time zone's regular UTC offset (as returned by getRawOffset()).

        This class returns 3600000 (1 hour) for time zones that use daylight savings time and 0 for timezones that do not, leaving it to subclasses to override this method for other daylight savings offsets. (There are time zones, such as Australia/Lord_Howe, that use other values.)

        Note that this method doesn't tell you whether or not to apply the offset: you need to call inDaylightTime for the specific time you're interested in. If this method returns a non-zero offset, that only tells you that this TimeZone sometimes observes daylight savings.

        Note also that this method doesn't necessarily return the value you need to apply to the time you're working with. This value can and does change over time for a given time zone.

        It's highly unlikely that you should ever call this method. You probably want getOffset(long) instead, which tells you the offset for a specific point in time, and takes daylight savings into account for you.

      • getOffset

        public int getOffset(long time)
        Returns the offset in milliseconds from UTC for this time zone at time. The offset includes daylight savings time if the specified date is within the daylight savings time period.
        Parameters:
        time - the date in milliseconds since January 1, 1970 00:00:00 UTC
      • getOffset

        public abstract int getOffset(int era,
                    int year,
                    int month,
                    int day,
                    int dayOfWeek,
                    int timeOfDayMillis)
        Returns this time zone's offset in milliseconds from UTC at the specified date and time. The offset includes daylight savings time if the date and time is within the daylight savings time period.

        This method is intended to be used by Calendar to compute Calendar.DST_OFFSET and Calendar.ZONE_OFFSET. Application code should have no reason to call this method directly. Each parameter is interpreted in the same way as the corresponding Calendar field. Refer to Calendar for specific definitions of this method's parameters.

      • getRawOffset

        public abstract int getRawOffset()
        Returns the offset in milliseconds from UTC of this time zone's standard time.
      • getTimeZone

        public static TimeZone getTimeZone(String id)
        Returns a TimeZone corresponding to the given id, or GMT for unknown ids.

        An ID can be an Olson name of the form Area/Location, such as America/Los_Angeles. The getAvailableIDs() method returns the supported names.

        This method can also create a custom TimeZone given an ID with the following syntax: GMT[+|-]hh[[:]mm]. For example, "GMT+05:00", "GMT+0500", "GMT+5:00", "GMT+500", "GMT+05", and "GMT+5" all return an object with a raw offset of +5 hours from UTC, and which does not use daylight savings. These are rarely useful, because they don't correspond to time zones actually in use by humans.

        Other than the special cases "UTC" and "GMT" (which are synonymous in this context, both corresponding to UTC), Android does not support the deprecated three-letter time zone IDs used in Java 1.1.

      • hasSameRules

        public boolean hasSameRules(TimeZone timeZone)
        Returns true if timeZone has the same rules as this time zone.

        The base implementation returns true if both time zones have the same raw offset.

      • inDaylightTime

        public abstract boolean inDaylightTime(Date time)
        Returns true if time is in a daylight savings time period for this time zone.
      • setDefault

        public static void setDefault(TimeZone timeZone)
        Overrides the default time zone for the current process only.

        Warning: avoid using this method to use a custom time zone in your process. This value may be cleared or overwritten at any time, which can cause unexpected behavior. Instead, manually supply a custom time zone as needed.

        Parameters:
        timeZone - a custom time zone, or null to set the default to the user's preferred value.
      • setID

        public void setID(String id)
        Sets the ID of this TimeZone.
      • setRawOffset

        public abstract void setRawOffset(int offsetMillis)
        Sets the offset in milliseconds from UTC of this time zone's standard time.
      • useDaylightTime

        public abstract boolean useDaylightTime()
        Returns true if this time zone has a future transition to or from daylight savings time.

        Warning: this returns false for time zones like Asia/Kuala_Lumpur that have previously used DST but do not currently. A hypothetical country that has never observed daylight savings before but plans to start next year would return true.

        Warning: this returns true for time zones that use DST, even when it is not active.

        Use inDaylightTime(java.util.Date) to find out whether daylight savings is in effect at a specific time.

        Most applications should not use this method.



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