Java is interpreted, not compiled; it's under the control of Oracle Corporation. It's probably fine for a prototyping language and for quick interactive demos. But it does add a layer of complexity, which slows things down (not a huge problem with today's hardware) and creates another failure point. Silly peasant vs. master race rants aside, it does not strike me as the wisest choice to implement a wallet in java.
Java is
compiled, there is an
implementation of java which basically exists because other corporations need a not-Oracle java, absolutely not under Oracle control, it has a very
cumbersome syntax and culture for prototyping, and has
approximately the same complexity as the C++ runtime.
How's EXO doing, anyway? This disinterred thread is the first I've heard of it.