Have you considered just using the javac compiler with ant as your build tool? The combination works well and you will not get burned by using a compiler that does not conform to the language standard: thus creating a lot of work when you do use a conforming compiler such as the latest release of JBuilder. Jikes is an excellent choice and you can use that with Ant and still keep your JBuilder for editing and such, if RealJ or Eclipse do not appeal to you.

http://oss.software.ibm.com/developerworks/opensource/jikes/