memory - How Java Program can be tuned or worked directly with available RAM (32 GB) and muti-core CPU processor -

i have high end machine 32 gb , want utilize available ram java process. practically, have seen can run @ max 3 jboss instances (or java process) max 3gb heap size in 1 box still have 20gb free space not utilized. possible create java program can directly work ram c++, not relying on java memory model creating objects on jvm , not relying on gc reclaim memory. mean java program directly working ram