java.util
Class TimeZone

java.lang.Object
  java.util.TimeZone

All Implemented Interfaces:

Cloneable, Serializable

Direct Known Subclasses:

SimpleTimeZone

public abstract class TimeZone

extends Object

implements Serializable, Cloneable

TimeZone represents a time zone offset, and also figures out daylight savings.

Typically, you get a TimeZone using getDefault which creates a TimeZone based on the time zone where the program is running. For example, for a program running in Japan, getDefault creates a TimeZone object based on Japanese Standard Time.

You can also get a TimeZone using getTimeZone 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 TimeZone object with:

 TimeZone tz = TimeZone.getTimeZone("America/Los_Angeles");
 

You can use the getAvailableIDs method to iterate through all the supported time zone IDs. You can then choose a supported ID to get a TimeZone. 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:

 CustomID:
         GMT Sign Hours : Minutes
         GMT Sign Hours Minutes
         GMT Sign Hours
 Sign: one of
         + -
 Hours:
         Digit
         Digit Digit
 Minutes:
         Digit Digit
 Digit: one of
         0 1 2 3 4 5 6 7 8 9
 

Hours must be between 0 to 23 and Minutes must be between 00 to 59. For example, "GMT+10" and "GMT+0010" mean ten hours and ten minutes ahead of GMT, respectively.

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, "GMT" is used.

When creating a TimeZone, the specified custom time zone ID is normalized in the following syntax:

 NormalizedCustomID:
         GMT Sign TwoDigitHours : Minutes
 Sign: one of
         + -
 TwoDigitHours:
         Digit Digit
 Minutes:
         Digit Digit
 Digit: one of
         0 1 2 3 4 5 6 7 8 9
 

For example, TimeZone.getTimeZone("GMT-8").getID() returns "GMT-08:00".

Three-letter time zone IDs

For compatibility with JDK 1.1.x, some other three-letter time zone IDs (such as "PST", "CTT", "AST") are also supported. However, their use is deprecated 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.

Since:

JDK1.1

Author:

Mark Davis, David Goldsmith, Chen-Lieh Huang, Alan Liu

See Also:

Calendar, GregorianCalendar, SimpleTimeZone, Serialized Form

Field Summary

private static Hashtable	cachedLocaleData Cache to hold the SimpleDateFormat objects for a Locale.
private static TimeZone	defaultZone
(package private) static String	GMT_ID
private static int	GMT_ID_LENGTH
private String	ID The string identifier of this TimeZone.
static int	LONG A style specifier for getDisplayName() indicating a long name, such as "Pacific Standard Time."
private static int	ONE_DAY
private static int	ONE_HOUR
private static int	ONE_MINUTE
(package private) static long	serialVersionUID
static int	SHORT A style specifier for getDisplayName() indicating a short name, such as "PST."

Constructor Summary

TimeZone()
Sole constructor.

Method Summary

Object	clone() Creates a copy of this TimeZone.
static String[]	getAvailableIDs() Gets all the available IDs supported.
static String[]	getAvailableIDs(int rawOffset) Gets the available IDs according to the given time zone offset.
static TimeZone	getDefault() Gets the default TimeZone for this host.
String	getDisplayName() Returns a name of this time zone suitable for presentation to the user in the default locale.
String	getDisplayName(boolean daylight, int style) Returns a name of this time zone suitable for presentation to the user in the default locale.
String	getDisplayName(boolean daylight, int style, Locale locale) Returns a name of this time zone suitable for presentation to the user in the specified locale.
String	getDisplayName(Locale locale) Returns a name of this time zone suitable for presentation to the user in the specified locale.
int	getDSTSavings() Returns the amount of time to be added to local standard time to get local wall clock time.
String	getID() Gets the ID of this time zone.
abstract int	getOffset(int era, int year, int month, int day, int dayOfWeek, int milliseconds) Gets the time zone offset, for current date, modified in case of daylight savings.
int	getOffset(long date) Returns the offset of this time zone from UTC at the specified date.
(package private) int	getOffsets(long date, int[] offsets) Gets the raw GMT offset and the amount of daylight saving of this time zone at the given time.
abstract int	getRawOffset() Returns the amount of time in milliseconds to add to UTC to get standard time in this time zone.
private static String	getSystemGMTOffsetID() Gets the custom time zone ID based on the GMT offset of the platform.
private static String	getSystemTimeZoneID(String javaHome, String country) Gets the platform defined TimeZone ID.
static TimeZone	getTimeZone(String ID) Gets the TimeZone for the given ID.
private static TimeZone	getTimeZone(String ID, boolean fallback)
boolean	hasSameRules(TimeZone other) Returns true if this zone has the same rule and offset as another zone.
abstract boolean	inDaylightTime(Date date) Queries if the given date is in daylight savings time in this time zone.
private static TimeZone	parseCustomTimeZone(String id) Parses a custom time zone identifier and returns a corresponding zone.
static void	setDefault(TimeZone zone) Sets the TimeZone that is returned by the getDefault method.
void	setID(String ID) Sets the time zone ID.
abstract void	setRawOffset(int offsetMillis) Sets the base time zone offset to GMT.
abstract boolean	useDaylightTime() Queries if this time zone uses daylight savings time.

Methods inherited from class java.lang.Object

equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

SHORT

public static final int SHORT

A style specifier for getDisplayName() indicating a short name, such as "PST."

Since:

1.2

See Also:

LONG, Constant Field Values

LONG

public static final int LONG

A style specifier for getDisplayName() indicating a long name, such as "Pacific Standard Time."

Since:

1.2

See Also:

SHORT, Constant Field Values

ONE_MINUTE

private static final int ONE_MINUTE

See Also:

Constant Field Values

ONE_HOUR

private static final int ONE_HOUR

See Also:

Constant Field Values

ONE_DAY

private static final int ONE_DAY

See Also:

Constant Field Values

cachedLocaleData

private static Hashtable cachedLocaleData

Cache to hold the SimpleDateFormat objects for a Locale.

serialVersionUID

static final long serialVersionUID

See Also:

Constant Field Values

ID

private String ID

The string identifier of this TimeZone. This is a programmatic identifier used internally to look up TimeZone objects from the system table and also to map them to their localized display names. ID values are unique in the system table but may not be for dynamically created zones.

defaultZone

private static TimeZone defaultZone

GMT_ID

static final String GMT_ID

See Also:

Constant Field Values

GMT_ID_LENGTH

private static final int GMT_ID_LENGTH

See Also:

Constant Field Values

Constructor Detail

TimeZone

public TimeZone()

Sole constructor. (For invocation by subclass constructors, typically implicit.)

Method Detail

getOffset

public abstract int getOffset(int era,
                              int year,
                              int month,
                              int day,
                              int dayOfWeek,
                              int milliseconds)

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.

This method returns a historically correct offset if an underlying TimeZone implementation subclass supports historical Daylight Saving Time schedule and GMT offset changes.

Parameters:

era - the era of the given date.

year - the year in the given date.

month - the month in the given date. Month is 0-based. e.g., 0 for January.

day - the day-in-month of the given date.

dayOfWeek - the day-of-week of the given date.

milliseconds - the milliseconds in day in standard local time.

Returns:

the offset in milliseconds to add to GMT to get local time.

See Also:

Calendar.ZONE_OFFSET, Calendar.DST_OFFSET

getOffset

public int getOffset(long date)

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.

This method returns a historically correct offset value if an underlying TimeZone implementation subclass supports historical Daylight Saving Time schedule and GMT offset changes.

Parameters:

date - the date represented in milliseconds since January 1, 1970 00:00:00 GMT

Returns:

the amount of time in milliseconds to add to UTC to get local time.

Since:

1.4

See Also:

Calendar.ZONE_OFFSET, Calendar.DST_OFFSET

getOffsets

int getOffsets(long date,
               int[] offsets)

Gets the raw GMT offset and the amount of daylight saving of this time zone at the given time.

Parameters:

date - the milliseconds (since January 1, 1970, 00:00:00.000 GMT) at which the time zone offset and daylight saving amount are found

Returns:

the total amount of the raw GMT offset and daylight saving at the specified date.

See Also:

Calendar.ZONE_OFFSET, Calendar.DST_OFFSET

setRawOffset

public abstract void setRawOffset(int offsetMillis)

Sets the base time zone offset to GMT. This is the offset to add to UTC to get local time.

If an underlying TimeZone 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.

Parameters:

offsetMillis - the given base time zone offset to GMT.

getRawOffset

public abstract int getRawOffset()

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 raw offset.

If an underlying TimeZone 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).

Returns:

the amount of raw offset time in milliseconds to add to UTC.

See Also:

Calendar.ZONE_OFFSET

getID

public String getID()

Gets the ID of this time zone.

Returns:

the ID of this time zone.

setID

public void setID(String ID)

Sets the time zone ID. This does not change any other data in the time zone object.

Parameters:

ID - the new time zone ID.

getDisplayName

public final String getDisplayName()

Returns a name of this time zone suitable for presentation to the user in the default locale. This method returns the long name, not including daylight savings. If the display name is not available for the locale, then this method returns a string in the normalized custom ID format.

Returns:

the human-readable name of this time zone in the default locale.

Since:

1.2

getDisplayName

public final String getDisplayName(Locale locale)

Returns a name of this time zone suitable for presentation to the user in the specified locale. This method returns the long name, not including daylight savings. If the display name is not available for the locale, then this method returns a string in the normalized custom ID format.

Parameters:

locale - the locale in which to supply the display name.

Returns:

the human-readable name of this time zone in the given locale or in the default locale if the given locale is not recognized.

Since:

1.2

getDisplayName

public final String getDisplayName(boolean daylight,
                                   int style)

Returns a name of this time zone suitable for presentation to the user in the default locale. If the display name is not available for the locale, then this method returns a string in the normalized custom ID format.

Parameters:

daylight - if true, return the daylight savings name.

style - either LONG or SHORT

Returns:

the human-readable name of this time zone in the default locale.

Since:

1.2

getDisplayName

public String getDisplayName(boolean daylight,
                             int style,
                             Locale locale)

Returns a name of this time zone suitable for presentation to the user in the specified locale. If the display name is not available for the locale, then this method returns a string in the normalized custom ID format.

Parameters:

daylight - if true, return the daylight savings name.

style - either LONG or SHORT

locale - the locale in which to supply the display name.

Returns:

the human-readable name of this time zone in the given locale or in the default locale if the given locale is not recognized.

Throws:

IllegalArgumentException - style is invalid.

Since:

1.2

getDSTSavings

public int getDSTSavings()

Returns the amount of time to be added to local standard time to get local wall clock time.

The default implementation always returns 3600000 milliseconds (i.e., one hour) if this time zone observes Daylight Saving Time. Otherwise, 0 (zero) is returned.

If an underlying TimeZone implementation subclass supports historical Daylight Saving Time changes, this method returns the known latest daylight saving value.

Returns:

the amount of saving time in milliseconds

Since:

1.4

useDaylightTime

public abstract boolean useDaylightTime()

Queries if this time zone uses daylight savings time.

If an underlying TimeZone implementation subclass supports historical Daylight Saving Time schedule changes, the method refers to the latest Daylight Saving Time schedule information.

Returns:

true if this time zone uses daylight savings time, false, otherwise.

inDaylightTime

public abstract boolean inDaylightTime(Date date)

Queries if the given date is in daylight savings time in this time zone.

Parameters:

date - the given Date.

Returns:

true if the given date is in daylight savings time, false, otherwise.

getTimeZone

public static TimeZone getTimeZone(String ID)

Gets the TimeZone for the given ID.

Parameters:

ID - the ID for a TimeZone, 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.

Returns:

the specified TimeZone, or the GMT zone if the given ID cannot be understood.

getTimeZone

private static TimeZone getTimeZone(String ID,
                                    boolean fallback)

getAvailableIDs

public static String[] getAvailableIDs(int rawOffset)

Gets the available IDs according to the given time zone offset.

Parameters:

rawOffset - the given time zone GMT offset.

Returns:

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 savings behavior.

getAvailableIDs

public static String[] getAvailableIDs()

Gets all the available IDs supported.

Returns:

an array of IDs.

getSystemTimeZoneID

private static String getSystemTimeZoneID(String javaHome,
                                          String country)

Gets the platform defined TimeZone ID.

getSystemGMTOffsetID

private static String getSystemGMTOffsetID()

Gets the custom time zone ID based on the GMT offset of the platform. (e.g., "GMT+08:00")

getDefault

public static TimeZone getDefault()

Gets the default TimeZone for this host. The source of the default TimeZone may vary with implementation.

Returns:

a default TimeZone.

See Also:

setDefault(java.util.TimeZone)

setDefault

public static void setDefault(TimeZone zone)

Sets the TimeZone that is returned by the getDefault method. If zone is null, reset the default to the value it had originally when the VM first started.

Parameters:

zone - the new default time zone

See Also:

getDefault()

hasSameRules

public boolean hasSameRules(TimeZone other)

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.

Parameters:

other - the TimeZone object to be compared with

Returns:

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

clone

public Object clone()

Creates a copy of this TimeZone.

Overrides:

clone in class Object

Returns:

a clone of this TimeZone

See Also:

Cloneable

parseCustomTimeZone

private static final TimeZone parseCustomTimeZone(String id)

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)

Parameters:

id - a string of the custom ID form.

Returns:

a newly created TimeZone with the given offset and no daylight saving time, or null if the id cannot be parsed.