JadRetro is a Java decompiler helper supporting Java 1.5+ classes. JadRetro is not a decompiler itself, it is a class transformer helping some old (but good) Java decompilers to convert more class files and/or generate more correct source code.
LucidEngine is a simple layer over MIDP compatible phones that will let you write simple and old fashioned games using a specific language.
Every game you'll develop will basically work on all the devices (even not phones) LucidEngine as been ported.