Lines Matching full:time
5 parent: Date/Time
25 A time zone is a system that is used for relating local times in different
27 Time is three hours earlier than Eastern Time; when it's 6 P.M. in San
29 time zones to one another, all time zones are related to a common reference
32 For historical reasons, the reference point is Greenwich, England. Local time in
33 Greenwich is referred to as Greenwich Mean Time, or GMT. (This is similar, but
34 not precisely identical, to Universal Coordinated Time, or UTC. We use the two
36 seconds or historical behavior.) Using this system, Pacific Time is expressed as
38 Time is obtained from GMT by adding -8:00, that is, by subtracting 8 hours.
40 The offset differs in the summer because of daylight savings time, or DST. At
41 this point it is useful to define three different flavors of local time:
43 * **Standard Time**:
44 Standard Time is local time without a daylight savings time offset. For
45 example, in California, standard time is GMT-8:00; that is, 8 hours before
47 * **Daylight Savings Time**:
48 Daylight savings time is local time with a daylight savings time offset.
50 daylight savings time is GMT-7:00. Daylight savings time is observed in most
52 * **Wall Time**:
53 Wall time is what a local clock on the wall reads. In areas that observe
54 daylight savings time for part of the year, wall time is either standard
55 time or daylight savings time, depending on the date. In areas that do not
56 observe daylight savings time, wall time is equivalent to standard time.
58 ## Time Zones in ICU
60 ICU supports time zones through two classes:
63 `TimeZone` is an abstract base class that defines the time zone API. This API
64 supports conversion between GMT and local time.
67 standard time zones used today internationally.
78 call up a specific real-world time zone. It corresponds to the IDs defined
79 in the [IANA Time Zone datbase](https://www.iana.org/time-zones) used by UNIX
81 * A raw offset. This is the difference, in milliseconds, between a time zone's
82 standard time and GMT. Positive raw offsets are east of Greenwich.
83 * Factory methods and methods for handling the default time zone.
85 * An API to compute the difference between local wall time and GMT.
95 create the actual time zone objects. ICU maintains a comprehensive list of
96 current international time zones, as derived from the Olson data.
98 `TimeZone` maintains a static time zone object known as the *default time zone*.
99 This is the time zone that is used implicitly when the user does not specify
100 one. ICU attempts to match this to the host OS time zone. The user may obtain a
101 clone of the default time zone by calling `createDefault()` and may change the
102 default time zone by calling `setDefault()` or `adoptDefault()`.
106 When displaying the name of a time zone to the user, use the display name, not
108 method. A time zone may have three display names:
110 * Generic name, such as "Pacific Time".
111 * Standard name, such as "Pacific Standard Time".
112 * Daylight savings name, such as "Pacific Daylight Time".
118 is used by the date format classes to format and parse time zones.
123 difference between local time and GMT. This is a pure virtual API, so it is
126 ## Updating the Time Zone Data
128 Time zone data changes often in response to governments around the world
130 data from the [IANA Time Zone Database](http://www.iana.org/time-zones).
136 * ICU4J: Use the time zone update utility.
140 * Data is loaded from a .dat package file: replace the time zone resources
150 The ICU resource files required for time zone data updates are posted at
161 For ICU configurations that load data from a .dat package file, replace the time
189 In ICU versions older than 4.4 some of the time zone resources have slightly
197 containing them. For the time zone resources only, ICU will check this directory
203 * At ICU build time, by defining the C pre-processor variable
204 `U_TIMEZONE_FILES_DIR` to the run time path to the directory containing the
206 * At run time, by setting the environment variable `ICU_TIMEZONE_FILES_DIR` to
210 precedence. If either is defined, the time zone directory will be checked first,
211 meaning that time zone resource files placed there will override time zone
215 described for the .dat file update above, and copy them into the time zone res
221 one), then the time zone .res file can be placed there. Download the files as
246 ### Update the time zone data for ICU4J
248 The [ICU4J Time Zone Update Update
250 updating ICU4J jar files with the latest time zone data. Instructions for use
257 See the [Date and Time Zone Examples](examples.md) subpage.