Can I write programs for the LEGO RCX 2.0 in Java/C++?
I was looking into this just recently. There are libraries and also it seems there are other firmwares offering alternative operating systems you can embed on the Mindstorm.

For C++ you could try:


nxtOSEK is an alternative OS offering a C++ api
BrickOS is an alternative OS with a C/C++ development environment
NXT++ is a C++ lib for controlling the original Mindstorm with a C++ API (through BlueTooth or USB)


For java solutions might be:


leJOS an alternative OS with a JVM
The NXTComm Processing Library