Retroweaver

http://retroweaver.sourceforge.net/

from yusukeさんの日記
http://yusuke.homeip.net/diary/

Retroweaver is a bytecode weaver that enables you to take advantage of the new Java 1.5 language features, while still retaining total binary compatability with 1.4 virtual machines. Retroweaver operates by transforming Java class files compiled by a 1.5 compiler into version 1.4 class files which can then be run on any 1.4 virtual machine.

おぉ、これは面白いですね。1.4環境で動作すれば、Java5への移植版を作るのに使えそうです。