This document describes how to adopt ICU4J into your application.
Migration of application code can be done incrementally, meaning full adoption of all ICU4J function is not necessary to reap the benefits of using ICU4J. Migration can be done in the following four sequential steps:
1. Import changes
Some classes need only be replaced with the ICU equivalent class by changing the import statement (i.e. change java.* with com.ibm.icu.*).
Example: change references of java.text.Collator to com.ibm.icu.text.Collator
This should be done for the following classes:
- java.util.StringTokenizer (see Note)
Note: The Eclipse SDK did not adopt ICU's version of StringTokenizer at this time as it will cause a performance degradation vs. the default java.* implementation
2. Parallel APIs
In this case, you will want to use the corresponding classes and API’s in place of the ones that are included in the JDK (in the java.* packages).
Example: replace references of java.lang.Character with class com.ibm.icu.lang.UCharacter
The conversion of java.* classes to com.ibm.icu.* classes should be done as follows:
- java.lang.Character -> com.ibm.icu.lang.UCharacter
- java.lang.Character$UnicodeBlock -> com.ibm.icu.lang.UCharacter$UnicodeBlock",
- java.text.DateFormatSymbols -> com.ibm.icu.text.DateFormatSymbols
- java.text.DecimalFormatSymbols -> com.ibm.icu.text.DecimalFormatSymbols
- java.text.Format -> com.ibm.icu.text.UFormat
- java.text.MessageFormat -> com.ibm.icu.text.MessageFormat
- java.util.Calendar -> com.ibm.icu.util.Calendar
- java.util.Currency -> com.ibm.icu.util.Currency
- java.util.GregorianCalendar -> com.ibm.icu.util.GregorianCalendar
- java.util.SimpleTimeZone -> com.ibm.icu.util.SimpleTimeZone
- java.util.TimeZone -> com.ibm.icu.util.TimeZone
- java.util.Locale -> com.ibm.icu.util.ULocale
- java.util.ResourceBundle -> com.ibm.icu.util.UResourceBundle
Note: classes UCharacter, UResourceBundle and ULocale are not implemented in the replacement plug-in (see below) so if your application’s code needs to work with both the replacement plug-in and the real ICU4J plug-in then you will not be able to adopt these classes at this time.
Some code needs to be re-written to take utilize ICU function. Discovering code that needs to be re-structured in this manner will not be as systematic as in the previous two steps.
Example: use com.ibm.icu.text.BreakIterator to locate boundaries in text instead of iterating over a string and using java.lang.Character.isLetterOrDigit(string.charAt(idx)).
4. Utilize New Features
ICU adds additional function in some areas that is not provided by the JDK. In this case, new code would need to be written to take advantage of these new features.
Example: the class com.ibm.icu.text.Transliterator
The Eclipse SDK will be adopting the ICU4J APIs for Eclipse 3.2. The addition of the ICU4J plug-in adds on the order of 3MB worth of code. Some applications may not want to absorb ICU4J if the priority is size over adopting the ICU4J function. If this is the case for your application, you can download the replacement plug-in (com.ibm.icu.base) from the build page from which you obtained your Eclipse build, remove the com.ibm.icu plug-in and its source counterpart, and drop in the replacement plug-in. This is required because the Platform adopted the ICU APIs for 3.2 and so just removing the ICU plug-in will result in compilation errors. The replacement plug-in is about 100KB in size and simply calls through to the java.* packages (default JDK implementation) of the most commonly used classes and APIs in ICU4J. The classes that are implemented in the replacement plug-in are as follows:
Bugs in ICU4J
Bugs that are found in ICU4J should not be logged against Eclipse products or components, they should be logged against the ICU project at:
For more information about ICU4J visit the official home page:
ICU open source project site: