Can you be more specific about how you're dividing tasks between C and Java? If there's a server running in Java and you want the entire client to be C++, you could use something like SOAP to exchange data between the two languages. If you want the client itself to be some sort of Java/C++ hybrid, you'd probably want to use JNDI to tie the languages together. But that might be too much overhead for a game.

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Scott J. Kleper
Author, "Professional C++"
(Wrox, 2005)