Indeed Java is better for financial apps as it's easier to write safer code. No pointers to arbitrarily access memory, no buffer overruns, bound checking, etc.  C++  is is better choice for apps that require faster start up and native integration.  

Faster start up is totaly irrelevant for server apps that start once and run for weeks/months without shutting down. Native integration is not needed either. Funny to watch Exo having difficulty releasing linux version. Had he used Java instead, it would have been platform independent. There is absolutely no reason to write crypto (server side)   in C++. It's a bad choice for the job.  

It's fine to write crypto clients in C++, and indeed anyone can write Nxt client in C++ for Windows. The client interacts with server (written i Java) . On the client side faster start up and native integration with GUI would be more desirable.