java.util

Class TimeZone

java.lang.Object

java.util.TimeZone

All Implemented Interfaces:

Serializable, Cloneable

public abstract class TimeZone
extends Object
implements Cloneable, Serializable

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

See Also:

Calendar, Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
static int	LONG A style specifier for getDisplayName() indicating a long name, such as "Pacific Standard Time."
static int	SHORT A style specifier for getDisplayName() indicating a short name, such as "PST."

Constructor Summary

Constructors

Constructor and Description
TimeZone() Sole constructor.

Method Summary

Modifier and Type	Method and Description
Object	clone() Creates a copy of this TimeZone.
static String[]	getAvailableIDs() Gets all the available IDs supported.
static TimeZone	getDefault() Gets the default TimeZone for this host.
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.
abstract int	getRawOffset() Returns the amount of time in milliseconds to add to UTC to get standard time in this time zone.
static TimeZone	getTimeZone(String ID) Gets the TimeZone for the given ID.
boolean	hasSameRules(TimeZone other) Returns true if this zone has the same rule and offset as another zone.
void	setID(String ID) Sets the time zone ID.
abstract boolean	useDaylightTime() Queries if this TimeZone uses Daylight Saving Time.

Methods inherited from class java.lang.Object

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

Field Detail

LONG

public static final int LONG

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

See Also:

SHORT, Constant Field Values

SHORT

public static final int SHORT

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

See Also:

LONG, Constant Field Values

Constructor Detail

TimeZone

public TimeZone()

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

Method Detail

getAvailableIDs

public static String[] getAvailableIDs()

Gets all the available IDs supported.

Returns:

an array of IDs.

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.

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".

Returns:

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

clone

public Object clone()

Creates a copy of this TimeZone.

Overrides:

clone in class Object

Returns:

a clone of this TimeZone

See Also:

Cloneable

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 returns 3600000 milliseconds (i.e., one hour) if a call to useDaylightTime() returns true. Otherwise, 0 (zero) is returned.

If an underlying 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.

If the amount of saving time at any given time stamp is required, construct a Calendar with this TimeZone and the time stamp, and call Calendar.get(Calendar.DST_OFFSET).

Returns:

the amount of saving time in milliseconds

See Also:

getOffset(long), getOffset(int,int,int,int,int,int), Calendar.ZONE_OFFSET

getID

public String getID()

Gets the ID of this time zone.

Returns:

the ID of this time zone.

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.

See Also:

Calendar.ZONE_OFFSET, Calendar.DST_OFFSET

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

hasSameRules

public boolean hasSameRules(@Nullable
                            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

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.

useDaylightTime

public abstract boolean useDaylightTime()

Queries if this TimeZone uses Daylight Saving Time.

If an underlying 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.

Returns:

true if this TimeZone uses Daylight Saving Time, false, otherwise.

See Also:

Calendar.DST_OFFSET