Java is more strongly tied to OOP, the general design of which may take a different thought process to "standard procedural" coding of C and ASM.  At a higher level, you also think somewhat less of the underlying CPU (on the coding side, I'm sure the emulator itself still needs to consider ASM).

Since you're here (and if you respond), just out of interest: it's certainly nice to help both projects with your expertise, but is there any particular reason why you don't dedicate yourself to one project?  Maybe, do you see that both have their own purposes? (Java's portability vs C's speed?)