ReadMe for ICU4J

## International Components for Unicode for Java (ICU4J)

### Read Me for ICU4J 4.4.2.2

Release Date
August 24, 2011

Note: This is an update release of ICU4J 4.4. This release contains several bug fixes and updated data, but does not introduce any new APIs or functionalities.

For the most recent release, see the ICU4J download site.

### Contents

- Introduction to ICU4J
- Changes In This Release
- License Information
- Platform Dependencies
- How to Download ICU4J
- The Structure and Contents of ICU4J
- Where to Get Documentation
- How to Install and Build
- How to modularize ICU4J
- Trying Out ICU4J
- ICU4J Resource Information
- About ICU4J Time Zone
- Where to Find More Information
- Submitting Comments, Requesting Features and Reporting Bugs

### Introduction to ICU4J

The International Components for Unicode (ICU) library provides robust and full-featured Unicode services on a wide variety of platforms. ICU supports the most current version of the Unicode standard, including support for supplementary characters (needed for GB 18030 repertoire support).

Java provides a strong foundation for global programs, and IBM and the ICU team played a key role in providing globalization technology to Java. But because of its long release schedule, Java cannot always keep up with evolving standards. The ICU team continues to extend Java's Unicode and internationalization support, focusing on improving performance, keeping current with the Unicode standard, and providing richer APIs, while remaining as compatible as possible with the original Java text and internationalization API design.

ICU4J is an add-on to the regular JRE that provides:

- Collation – rule-based, up-to-date Unicode Collation Algorithm (UCA) sorting order
  For fast multilingual string comparison; faster and more complete than the J2SE implementation
- Supplementary Characters – String manipulation and character properties
  Required for proper GB 18030 and JIS X 0213 repertoire support
- Charset Detection – Recognition of various single and multibyte charsets
  Useful for recognizing untagged text data
- UnicodeSet – standard set operations optimized for sets of Unicode characters
  UnicodeSets can be built from string patterns using any Unicode properties.
- Transforms – a flexible mechanism for Unicode text conversions
  Including Full/Halfwidth conversions, Normalization, Case conversions, Hex conversions, and transliterations between scripts (50+ pairs)
- Unicode Normalization – NFC, NFD, NFKD, NFKC
  For canonical text representations, needed for XML and the net
- International Calendars – Arabic, Buddhist, Chinese, Hebrew, Japanese, Ethiopic, Islamic, Coptic and other calendars
  Required for correct presentation of dates in certain countries
- Number Format Enhancements – Scientific Notation, Spelled-out, etc.
  Enhancements to the normal Java number formatting. The spell-out format is used for checks and similar documents
- Enhanced Word-Break Detection – Rule-based, supports Thai
  Required for correct support of Thai
- Unicode Text Compression – Standard compression of Unicode text
  Suitable for large numbers of small fields, where LZW and similar schemes do not apply
- Charset Conversion – Conversion to and from different charsets.
  Plugs into Java CharsetProvider Service Provider Interface (SPI)

> Note: We continue to provide assistance to Sun, and in some cases, ICU4J support has been rolled into a later release of Java. For example, the Thai word-break is now in Java 1.4. However, the most current and complete version is always found in ICU4J.

### Changes In This Release

#### Minimum Java runtime environment requirement

Starting with version 4.4, you need at least JRE 5.0 to use ICU4J 4.4. ICU4J adopted Java 5 language features and no longer compiles with JDK 1.4 or older versions. This migration also includes some updates in public API signatures, such as generics and return/parameter types. In general, most of these changes do not require any changes in existing ICU4J user code.

#### TimeZone serialization compatibility

The new system time zone data format supporting 64bit transition time data implemented in ICU4J 4.4 introduced a serialization incompatibility issue in the internal TimeZone implementation class (e.g. An instance of TimeZone created by `TimeZone.getTimeZone(String)` with an Olson tzid, such as `"America/Los_Angeles"`). The new implementation reads only the system time zone identifier string when object data was serialized by ICU4J 4.2 or older versions. Also, ICU4J 4.2 or older versions cannot read object data created by ICU4J 4.4. The system time zone implementation class may be used by other ICU4J public API classes, such as `Calendar` and `DateFormat`, therefore, these classes are also affected.

For the ICU4J serialization compatibility policy, please refer the user guide section ICU4J Serialization Compatibility.

#### New features and other changes

See the ICU 4.4 download page about new features in this release. The list of API changes since the previous ICU4J release is available here.

#### Summary of updates in 4.4.2.2 (August 24, 2011)

Java 7 Locale support

Java 7 was shipped in July 2011 including some enhancements in java.util.Locale class. For supporting the enhancements in Locale class, ICU4J com.ibm.icu.util.ULocale was also updated in the latest code stream by following tickets.

- #8078 ICU4J APIs taking Locale to use new JDK7 APIs to access script/extensions
- #8630 Java 7 Locale Category support

These changes in ULocale class were back-ported to this release. (Note: The new APIs for locale category are tagged as @stable ICU 49, indicating these APIs are back-ported from later code stream.)

Bug fixes

This release contains following bug fixes

- #6108 DecimalFormat fraction digit problem with rounding + BigDecimal
- #8410 In IndianCalendar, the add operation performs like roll
- #8484 endless loop in RuleBasedCollator.getSortKeyBytes
- #8549 UTF-7 error handling consumes too many valid subsequent chars
- #8569 UTF-7 missing terminating shift character
- #8596 GregorianCalendar.getActualMaximum(Calendar.WEEK_OF_YEAR) returns 52 when it should return 53
- #8624 ucol_getSortKey+strncmp and ucol_strcoll give different comparison result

#### Summary of updates in 4.4.2.1 (July 1, 2011)

ICU4J plug-in for Eclipse 3.7

ICU4J 4.4.2.1 source archive includes files for building ICU4J plug-in for Eclipse 3.7.

Tme zone data update

ICU4J 4.4.2.1 updates the time zone data to version 2011h from the Olson tz database.

Bug fix

This release contains following bug fix

- #7201 Transliterator is not thread safe
- #7480 Wrong year from SimpleDateFormat.parse()
- #7690 OlsonTimeZone.hashCode() throws NullPointerException
- #7880 Race in VersionInfo.getInstance()
- #8275 ICU4J Locale service returns incorrect result with unsupported class loader protocol
- #8283 ICU4J MessageFormat should use varargs in format method
- #8258 Avoid UnicodeSet constructors taking String pattern when all code points are known
- #8259 Use Java StringTokenizer instead of ICU in ICUResourceBundle and VTimeZone

#### Summary of updates in 4.4.2 (October 1, 2010)

Tme zone data update

ICU4J 4.4.2 updates the time zone data to version 2010m from the Olson tz database.

Bug fix

This release contains following bug fix

- #7922 ICU4J charset converter aliases do not work on z/OS
- #7927 Updated LMBCS mapping table
- #7941 CopticTest/Test6379 failure

#### Summary of updates in 4.4.1.1 (June 21, 2010)

Tme zone data update

ICU4J 4.4.1.1 updates the time zone data to version 2010j from the Olson tz database.

Bug fix

This release contains following bug fix

- #7765 ICU4J 4.4 fails to load available locales on WebSphere

#### Summary of updates in 4.4.1 (April 28, 2010)

CLDR 1.8.1 updates

ICU4J 4.4.1 imported locale data updates from CLDR 1.8.1 release.

Time zone data update

ICU4J 4.4.1 updates the time zone data to version 2010i from the Olson tz database.

Bug fixes

This release contains following bug fixes

- #7395 gatherapi tool doesn't handle 'synthetic' methods
- #7594 Serialization CoverageTest is broken in ICU 4.4
- #7595 SimpleDateFormat fails to handle very long field patterns
- #7644 Enable non-Gregorian calendars for DateIntervalFormat

### License Information

The ICU projects (ICU4C and ICU4J) use the X license. The X license is suitable for commercial use and is a recommended free software license that is compatible with the GNU GPL license. This became effective with release 1.8.1 of ICU4C and release 1.3.1 of ICU4J in mid-2001. All new ICU releases will adopt the X license; previous ICU releases continue to utilize the IPL (IBM Public License). Users of previous releases of ICU who want to adopt new ICU releases will need to accept the terms and conditions of the X license.

The main effect of the change is to provide GPL compatibility. The X license is listed as GPL compatible, see the GNU page at http://www.gnu.org/philosophy/license-list.html#GPLCompatibleLicenses. This means that GPL projects can now use ICU code, it does not mean that projects using ICU become subject to GPL.

The IBM version contains the essential text of the license, omitting the X-specific trademarks and copyright notices. The full copy of ICU's license is included in the download package.

### Platform Dependencies

ICU4J 4.4 depends on J2SE 5.0 functionality. Therefore, ICU4J only runs on JRE version 5.0 or later. The table below shows the operating systems and JRE/VM versions currently used by the ICU development team to test ICU4J.

Operating System | JRE/Hotspot | JRE/IBM J9
--- | --- | ---
1.6.0 | 1.5.0 | 1.6.0 | 1.5.0
32bit | 64bit | 32bit | 64bit | 32bit | 64bit | 32bit | 64bit
AIX 5.3 | - | - | - | - | - | Regularly tested | - | Regularly tested
AIX 6.1 | - | - | - | - | - | Reference platform | - | Regularly tested
HP-UX 11 (PA-RISC) | - | Regularly tested | - | Regularly tested | - | - | - | -
HP-UX 11 (IA64) | - | Regularly tested | - | Regularly tested | - | - | - | -
Mac OS X 10.5 | - | Regularly tested | Regularly tested | - | - | - | - | -
Redhat Enterprise Linux 5 (x86) | Regularly tested | - | Regularly tested | - | Regularly tested | - | Regularly tested | -
Redhat Enterprise Linux 5 (x86_64) | - | Regularly tested | - | Regularly tested | - | Regularly tested | - | Regularly tested
Solaris 9 (SPARC) | Regularly tested | - | Regularly tested | - | - | - | - | -
Solaris 10 (SPARC) | - | Reference platform | - | Regularly tested | - | - | - | -
Windows XP | Regularly tested | - | Regularly tested | - | Regularly tested | - | Regularly tested | -
Windows Vista | Regularly tested | - | Regularly tested | - | Regularly tested | - | Regularly tested | -
Windows 7 | Regularly tested | - | Regularly tested | - | Reference platform | - | Regularly tested | -
Windows 2008 Server | - | Regularly tested | - | Regularly tested | - | Regularly tested | - | Regularly tested

### How to Download ICU4J

There are two ways to download the ICU4J releases.

- Official Release:
  If you want to use ICU4J (as opposed to developing it), your best bet is to download an official, packaged version of the ICU4J library files. These versions are tested more thoroughly than day-to-day development builds, and they are packaged in jar files for convenient download. These packaged files can be found at the ICU Download page.

- Subversion Source Repository:
  If you are interested in developing features, patches, or bug fixes for ICU4J, you should probably be working with the latest version of the ICU4J source code. You will need to check the code out of our Subversion repository to ensure that you have the most recent version of all of the files. There are several ways to do this. Please follow the directions that are contained on the Source Repository page for details.

For more details on how to download ICU4J directly from the web site, please see the ICU download page at http://www.icu-project.org/download/

### The Structure and Contents of ICU4J

Below, all directory pathes are relative to the directory where the ICU4J source archive is extracted.

Information and build files:

Path | Description
--- | ---
readme.html | A description of ICU4J (International Components for Unicode for Java)
build.html | The main Ant build file for ICU4J. See How to Install and Build for more information
main/shared/licenses/license.html | The X license, used by ICU4J

ICU4J runtime class files:

Path | Sub-component Name | Build Dependencies | Public API Packages | Description
--- | --- | --- | --- | ---
main/classes/charset | icu4j-charset | icu4j-core | com.ibm.icu.charset | Implementation of `java.nio.charset.spi.CharsetProvider`. This sub-component is shipped as icu4j-charsets.jar along with ICU charset converter data files.
main/classes/collate | icu4j-collate | icu4j-core | com.ibm.icu.text com.ibm.icu.util | Collator APIs and implementation. Also includes some public API classes that depend on Collator. This sub-component is packaged as a part of icu4j.jar.
main/classes/core | icu4j-core | n/a | com.ibm.icu.lang com.ibm.icu.math com.ibm.icu.text com.ibm.icu.util | ICU core API classes and implementation. This sub-component is packaged as a part of icu4j.jar.
main/classes/currdata | icu4j-currdata | icu4j-core | n/a | No public API classes. Provides access to currency display data. This sub-component is packaged as a part of icu4j.jar.
main/classes/langdata | icu4j-langdata | icu4j-core | n/a | No public API classes. Provides access to language display data. This sub-component is packaged as a part of icu4j.jar.
main/classes/localespi | icu4j-localespi | icu4j-core icu4j-collate | n/a | Implementation of various locale-sensitive service providers defined in `java.text.spi` and `java.util.spi` in J2SE 6.0 or later Java releases. This sub-component is shipped as icu4j-localespi.jar.
main/classes/regiondata | icu4j-regiondata | icu4j-core | n/a | No public API classes. Provides access to region display data. This sub-component is packaged as a part of icu4j.jar.
main/classes/translit | icu4j-translit | icu4j-core | com.ibm.icu.text | Transliterator APIs and implementation. This sub-component is packaged as a part of icu4j.jar.

ICU4J unit test files:

Path | Sub-component Name | Runtime Dependencies | Description
--- | --- | --- | ---
main/tests/charset | icu4j-charset-tests | icu4j-charset icu4j-core icu4j-test-framework | Test suite for charset sub-component.
main/tests/collate | icu4j-collate-tests | icu4j-collate icu4j-core icu4j-test-framework | Test suite for collate sub-component.
main/tests/core | icu4j-core-tests | icu4j-core icu4j-currdata icu4j-langdata icu4j-regiondata icu4j-test-framework | Test suite for core sub-component.
main/tests/framework | icu4j-test-framework | icu4j-core | Common ICU4J unit test framework and utilities.
main/tests/localespi | icu4j-localespi-tests | icu4j-core icu4j-collate icu4j-currdata icu4j-langdata icu4j-localespi icu4j-regiondata icu4j-test-framework | Test suite for localespi sub-component.
main/tests/packaging | icu4j-packaging-tests | icu4j-core icu4j-test-framework | Test suite for sub-component packaging.
main/tests/translit | icu4j-translit-tests | icu4j-core icu4j-translit icu4j-test-framework | Test suite for translit sub-component.

Others:

Path | Description
--- | ---
main/shared | Files shared by ICU4J sub-components under the `main` directory including: ICU4J runtime data archive (icudata.jar). ICU4J unit test data archive (testdata.jar). Shared Ant build script and configuration files. License files.
demos | ICU4J demo programs.
perf-tests | ICU4J performance test files.
tools | ICU4J tools including: Custom JavaDoc taglets used for generating ICU4J API references. API report tool and data. Other independent utilities used for ICU4J development.

### Where to get Documentation

The ICU user's guide contains lots of general information about ICU, in its C, C++, and Java incarnations.

The complete API documentation for ICU4J (javadoc) is available on the ICU4J web site, and can be built from the sources:

- Index to all ICU4J API
- Charset Detector – Detection of charset from a byte stream
- International Calendars – Buddhist, Chinese, Coptic, Ethiopic, Gregorian, Hebrew, Indian, Islamic, Japanese.
- Unicode Normalization – Canonical text representation for W3C.
- Number Format Enhancements – Scientific Notation, Spelled out.
- Enhanced word-break detection – Rule-based, supports Thai
- Transliteration – A general framework for converting text from one format to another, e.g. Cyrillic to Latin, or Hex to Unicode.
- Unicode Text Compression & Decompression – 2:1 compression on English Unicode text.
- Collation - Rule-based sorting, Efficient multi-lingual searching

### How to Install and Build

To install ICU4J, simply place the prebuilt jar file icu4j.jar on your Java CLASSPATH. If you need Charset API support please also place icu4j-charsets.jar on your class path along with icu4j.jar.

To build ICU4J, you will need J2SE SDK 5.0 or later (ICU4J locale SPI provider sub-components require J2SE SDK 6.0 or later) and the Ant build system version 1.7 or later. It's recommended to install both the J2SE SDK and Ant somewhere outsidethe ICU4J directory. For example, on Linux you might install these in `/usr/local`.

- Install J2SE SDK 6.0.
- Install the Ant build system. Ant is a portable, Java-based build system similar to make. ICU4J uses Ant because it introduces no other dependencies, it's portable, and it's easier to manage than a collection of makefiles. We currently build ICU4J using a single makefile on all platforms Ant. The build system requires Ant 1.7 or later.

  Installing Ant is straightforward. Download it (see http://ant.apache.org/bindownload.cgi), extract it onto your system, set some environment variables, and add its bin directory to your path. For example:

              set JAVA_HOME=C:\jdk1.6.0
              set ANT_HOME=C:\ant
              set PATH=%PATH%;%ANT_HOME%\bin

  See the current Ant documentation for details.

Once the J2SE SDK and Ant are installed, building is just a matter of typing ant in the ICU4J root directory. This causes the Ant build system to perform the build target jar as specified by the file build.xml, located in the ICU4J root directory. You can give Ant options like -verbose, and you can specify other targets. For example:

>     C:\icu4j>ant
>     Buildfile: build.xml

>     info:
>          [echo] ----- Build Environment Information -------------------
>          [echo] Java Home:    C:\jdk1.6.0
>          [echo] Java Version: 1.6.0
>          [echo] Ant Home:     C:\ant
>          [echo] Ant Version:  Apache Ant version 1.7.1 compiled on June 27 2008
>          [echo] OS:           Windows Vista
>          [echo] OS Version:   6.1 build 7600
>          [echo] OS Arch:      x86
>          [echo] Host:         ICUDEV
>          [echo] -------------------------------------------------------

>     core:

>     @compile:
>          [echo] --- java compiler arguments ------------------------
>          [echo] source dir:     C:\icu4j\main\classes\core/src
>          [echo] output dir:     C:\icu4j\main\classes\core/out/bin
>          [echo] classpath:
>          [echo] source:         1.5
>          [echo] target:         1.5
>          [echo] debug:          on
>          [echo] encoding:       ascii
>          [echo] compiler arg:   -Xlint:all,-deprecation,-dep-ann
>          [echo] ----------------------------------------------------
>         [mkdir] Created dir: C:\icu4j\main\classes\core\out\bin
>         [javac] Compiling 316 source files to C:\icu4j\main\classes\core\out\bin
>         [javac] Note: Some input files use or override a deprecated API.
>         [javac] Note: Recompile with -Xlint:deprecation for details.

>     compile:

>     @copy:
>          [copy] Copying 23 files to C:\icu4j\main\classes\core\out\bin

>     copy-data:
>         [unjar] Expanding: C:\icu4j\main\shared\data\icudata.jar into C:\icu4j\main\classes\core\out\bin

>     ....
>     ....
>     ....

>     build:

>     _build-localespi:

>     @compile:
>          [echo] --- java compiler arguments ------------------------
>          [echo] source dir:     C:\icu4j\main\classes\localespi/src
>          [echo] output dir:     C:\icu4j\main\classes\localespi/out/bin
>          [echo] classpath:      C:\icu4j\main\classes\core\out\lib\icu4j-core.jar;C:\icu4j\main\classes\collate\
>     out\lib\icu4j-collate.jar
>          [echo] source:         1.6
>          [echo] target:         1.6
>          [echo] debug:          on
>          [echo] encoding:       ascii
>          [echo] compiler arg:   -Xlint:all,-deprecation,-dep-ann
>          [echo] ----------------------------------------------------
>         [mkdir] Created dir: C:\icu4j\main\classes\localespi\out\bin
>         [javac] Compiling 22 source files to C:\icu4j\main\classes\localespi\out\bin

>     compile:

>     @copy:
>          [copy] Copying 10 files to C:\icu4j\main\classes\localespi\out\bin

>     copy:

>     @jar:
>         [mkdir] Created dir: C:\icu4j\main\classes\localespi\out\lib
>          [copy] Copying 1 file to C:\icu4j\main\classes\localespi\out
>           [jar] Building jar: C:\icu4j\main\classes\localespi\out\lib\icu4j-localespi.jar

>     jar:

>     build:

>     jar:
>          [copy] Copying 1 file to C:\icu4j
>          [copy] Copying 1 file to C:\icu4j

>     BUILD SUCCESSFUL
>     Total time: 24 seconds

Note: The above output is an example. The numbers are likely to be different with the current version ICU4J.

The following are some targets that you can provide to ant. For more targets run `ant -projecthelp` or see the build.xml file.

jar (default) | Create ICU4J runtime library jar archives (`icu4j.jar`, `icu4j-charsets.jar` and `icu4j-localespi.jar`) in the root ICU4J directory.
check | Build all ICU4J runtime library classes and corresponding unit test cases, then run the tests.
clean | Remove all build output files.
main | Build all ICU4J runtime library sub-components (under the directory `main/classes`).
tests | Build all ICU4J unit test sub-components (under the directory `main/tests`) and their dependencies.
tools | Build the tools.
docs | Run javadoc over the ICU4J runtime library files, generating an HTML documentation tree in the subdirectory `doc`.
jarDocs | Create ICU4J doc jar archive (`icu4jdocs.jar`) containing API reference docs in the root ICU4J directory.
jarDemos | Create ICU4J demo jar archive (`icu4jdemos.jar`) in the root ICU4J directory.

For more information, read the Ant documentation and the build.xml file.

Note: If you get an OutOfMemoryError when you are running `"ant check"`, you can set the heap size of the jvm by setting the environment variable JVM_OPTIONS to the appropriate java options.

Eclipse users: See the ICU4J site for information on how to configure Eclipse to build and develop ICU4J on Eclipse IDE.

Note: To install ICU4J Locale Service Provider, please refer Read Me for ICU4J Locale Service Provider.

### How to modularize ICU4J

Some clients may not wish to ship all of ICU4J with their application, since the application might only use a small part of ICU4J. ICU4J release 2.6 and later provide build options to build individual ICU4J 'modules' for a more compact distribution. For more details, please refer to the section Modularization of ICU4J in the ICU user's guide article Packaging ICU4J.

### Trying Out ICU4J

Note: the demos provided with ICU4J are for the most part undocumented. This list can show you where to look, but you'll have to experiment a bit. The demos are unsupported and may change or disappear without notice.

The icu4j.jar file contains only the ICU4J runtime library classes, not the demo classes, so unless you build ICU4J there is little to try out.

#### Charset

To try out the Charset package, build icu4j.jar and icu4j-charsets.jar using the 'jar' target. You can use the charsets by placing these files on your classpath.

> `java -cp $icu4j_root/icu4j.jar:$icu4j_root/icu4j-charsets.jar <your program>`

#### Other demos

The other demo programs are not supported and exist only to let you experiment with the ICU4J classes. First, build ICU4J using `ant jarDemos`. Then launch the demos as below:

> `java -jar $icu4j_root/icu4jdemos.jar`

### ICU4J Resource Information

Starting with release 2.1, ICU4J includes its own resource information which is completely independent of the JRE resource information. (Note, ICU4J 2.8 to 3.4, time zone information depends on the underlying JRE). The ICU4J resource information is equivalent to the information in ICU4C and many resources are, in fact, the same binary files that ICU4C uses.

By default the ICU4J distribution includes all of the standard resource information. It is located under the directory com/ibm/icu/impl/data. Depending on the service, the data is in different locations and in different formats. Note: This will continue to change from release to release, so clients should not depend on the exact organization of the data in ICU4J.

- The primary locale data is under the directory `icudt44b`, as a set of `".res"` files whose names are the locale identifiers. Locale naming is documented the `com.ibm.icu.util.ULocale` class, and the use of these names in searching for resources is documented in `com.ibm.icu.util.UResourceBundle`.
- The collation data is under the directory `icudt44b/coll`, as a set of `".res"` files.
- The currency display name data is under the directory `icudt44b/curr`, as a set of `".res"` files.
- The language display name data is under the directory `icudt44b/lang`, as a set of `".res"` files.
- The region display name data is under the directory `icudt44b/region`, as a set of `".res"` files.
- The rule-based transliterator data is under the directory `icudt44b/translit`, as a set of `".res"` files.
- The rule-based number format data is under the directory `icudt44b/rbnf`, as a set of `".res"` files.
- The break iterator data is directly under the directory `icudt44b`, as a set of `".brk"` files, named according to the type of break and the locale where there are locale-specific versions.
- The holiday data is under the directory `icudt44b`, as a set of `".class"` files, named `"HolidayBundle_"` followed by the locale ID.
- The character property data as well as assorted normalization data and default unicode collation algorithm (UCA) data is found under the directory `icudt44b`, as a set of `".icu"` files.
- The character set converter data is under the directory `icudt44b`, as a set of `".cnv"` files. These files are currently included only in icu-charset.jar.
- The time zone rule data is under the directory `icudt44b`, as `zoneinfo64.res`.
- The time zone display name data is under the directory `icudt44b/zone`, as a set of `".res"` files.

Some of the data files alias or otherwise reference data from other data files. One reason for this is because some locale names have changed. For example, `he_IL` used to be `iw_IL`. In order to support both names but not duplicate the data, one of the resource files refers to the other file's data. In other cases, a file may alias a portion of another file's data in order to save space. Currently ICU4J provides no tool for revealing these dependencies.

> Note: Java's `Locale` class silently converts the language code `"he"` to `"iw"` when you construct the Locale (for versions of Java through Java 5). Thus Java cannot be used to locate resources that use the `"he"` language code. ICU, on the other hand, does not perform this conversion in ULocale, and instead uses aliasing in the locale data to represent the same set of data under different locale ids.

Resource files that use locale ids form a hierarchy, with up to four levels: a root, language, region (country), and variant. Searches for locale data attempt to match as far down the hierarchy as possible, for example, `"he_IL"` will match `he_IL`, but `"he_US"` will match `he` (since there is no `US` variant for he, and `"xx_YY` will match root (the default fallback locale) since there is no `xx` language code in the locale hierarchy. Again, see `java.util.ResourceBundle` for more information.

Currently ICU4J provides no tool for revealing these dependencies between data files, so trimming the data directly in the ICU4J project is a hit-or-miss affair. The key point when you remove data is to make sure to remove all dependencies on that data as well. For example, if you remove `he.res`, you need to remove `he_IL.res`, since it is lower in the hierarchy, and you must remove iw.res, since it references `he.res`, and `iw_IL.res`, since it depends on it (and also references `he_IL.res`).

Unfortunately, the jar tool in the JDK provides no way to remove items from a jar file. Thus you have to extract the resources, remove the ones you don't want, and then create a new jar file with the remining resources. See the jar tool information for how to do this. Before 'rejaring' the files, be sure to thoroughly test your application with the remaining resources, making sure each required resource is present.

#### Using additional resource files with ICU4J

> Warning: Resource file formats can change across releases of ICU4J!
> The format of ICU4J resources is not part of the API. Clients who develop their own resources for use with ICU4J should be prepared to regenerate them when they move to new releases of ICU4J.

We are still developing ICU4J's resource mechanism. Currently it is not possible to mix icu's new binary `.res` resources with traditional java-style `.class` or `.txt` resources. We might allow for this in a future release, but since the resource data and format is not formally supported, you run the risk of incompatibilities with future releases of ICU4J.

Resource data in ICU4J is checked in to the repository as a jar file containing the resource binaries, `icudata.jar`. This means that inspecting the contents of these resources is difficult. They currently are compiled from ICU4C `.txt` file data. You can view the contents of the ICU4C text resource files to understand the contents of the ICU4J resources.

The files in `icudata.jar` get extracted to `com/ibm/icu/impl/data` in the build directory when the 'core' target is built. Building the `'resources'` target will force the resources to once again be extracted. Extraction will overwrite any corresponding resource files already in that directory.

#### Building ICU4J Resources from ICU4C

ICU4J data is built by ICU4C tools. Please see "icu4j-readme.txt" in $icu4c_root/source/data for the procedures.

##### Generating Data from CLDR

Note: This procedure assumes that all 3 sources are in sibling directories

1. Checkout CLDR. $cldr_root in the following steps is the root directory where the CLDR source files checked out.
2. Update $cldr_root/common to 'release-1-8-1' tag
3. Update $cldr_root/tools to 'release-1-8-1' tag
4. Checkout ICU4C with tag 'release-4-4-2'
5. Checkout ICU4J with tag 'release-4-4-2-2'
6. Build ICU4J
7. Build ICU4C
8. Change to $cldr_root/tools/java directory
9. Build CLDR using ant after pointing ICU4J_CLASSES env var to the newly build ICU4J
10. cd to $icu4c_root/source/data directory
11. Follow the instructions in the cldr-icu-readme.txt
12. Build ICU4C data from CLDR
13. Build ICU4J data from ICU4C data by following the procedures in $icu4c_root/source/data/icu4j-readme.txt
14. cd to $icu4j_root dir
15. Build and test icu4j

### About ICU4J Time Zone

ICU4J 4.4.2.2 includes time zone data version 2011h, which is the latest one as of the release date. However, time zone data is frequently updated in response to changes made by local governments around the world. If you need to update the time zone data, please refer the ICU user guide topic Updating the Time Zone Data.

Starting with ICU4J 4.0, you can optionally configure ICU4J date and time service classes to use underlying JDK TimeZone implementation (see the ICU4J API reference TimeZone for the details). When this configuration is enabled, ICU's own time zone data won't be used and you have to get time zone data patches from the JRE vendor.

### Where to Find More Information

http://www.icu-project.org/ is the home page of International Components for Unicode development project

http://www.ibm.com/software/globalization/icu/ is a pointer to general information about the International Components for Unicode hosted by IBM

http://www.ibm.com/software/globalization/ is a pointer to information on how to make applications global.

### Submitting Comments, Requesting Features and Reporting Bugs

Your comments are important to making ICU4J successful. We are committed to investigate any bug reports or suggestions, and will use your feedback to help plan future releases.

To submit comments, request features and report bugs, please see ICU bug database information or contact us through the ICU Support mailing list. While we are not able to respond individually to each comment, we do review all comments.

## Thank you for your interest in ICU4J!

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