A complete description of the API changes between version 3.0 and version 2.8 of ICU4J -can be found here.
+A complete report of the API changes between version 3.0 and +version 2.8 of ICU4J can be found here. This report is generated by a +tool and has some limitations, the most notable of which is that it +does not properly reflect the effect of class inheritance changes. For +example, ICU4J 3.0 moved the definition of some constants out of +some classes into interfaces that the classes now inherit, and +although this has no impact on the API available to the classes, the +tool reports this as a removal of API from them. Also of course, +being generated by a tool, the report does not provide explanation or +commentary on the changes. For background information and +clarification of changes it's always recommended that you check the +mailing list and archives.
RFC 3066 defines a new format for Locale identifiers that +incorporates information about the script as well as the language and +region into the locale identifier. ICU4J has enhanced the +ULocale class to provide this information. ICU4J has also added +the UResourceBundle class to allow instantiation of resource +bundles using RFC 3066-style locale ids. This is an +initial implementation; not all ICU4J APIs that currently work with +Locale have been enhanced to work with ULocale. We +anticipate a complete implementation in the next ICU4J release.
+ +JDK 1.5 introduces new APIs for surrogate support. ICU4J has +offered surrogate support for several releases, and continues to offer +this functionality. However, to simplify porting between ICU4J and +JDK 1.5, where possible ICU4J has added APIs that provide the same +signature and semantics as those planned for 1.5. (There are some +unavoidable differences, for example, APIs added to java.lang.String +cannot be exactly matched by ICU4J). Members of the ICU team +participated in the JSR 204 expert group discussions and helped +develop the new Java APIs for supplementary character support.
+RFC 3066 defines a new format for Locale identifiers that -incorporates information about the script as well as the language and -region into the locale identifier. ICU4J has enhanced the -ULocale class to provide this information. This is an -initial implementation; not all ICU4J APIs that currently work with -Locale have been enhanced to work with ULocale. We -anticipate a complete implementation in the next ICU4J release.
-ICU4J has switched to a new resource bundle implementation in order to utilize the same binary data files used by ICU. This will likely impact clients who have extended or modified the resource data provided in ICU4J. Most clients will -see no change from this switchover.
+see no change from this switchover. This change was made for several reasons, +the main ones being the desire to provide RFC 3066 support in a manner identical +to ICU, to avoid reworking the conversion tools (genrb) each time we evolve ICU's +resource bundle structure, and to avoid certain size constraints imposed by +java's class file format.