Oracle could pull all resources dedicated to the development of Java. Burn the forest to get the Google tree.
Drastic and unrealistic, but Ellison doesn't like to lose.
a) Java customers tend to also use Oracle DB and Solaris, two other big Oracle products. Revenge on Google can't be worth giving up owning the full stack.
b) Google (perhaps with IBM and Red Hat) would be absolutely delighted to pick up Java development were Oracle to stop working on it; quite the opposite of what Oracle would hope to accomplish.
C/C++ doesn't seem to have done too badly since Bell labs stopped developing it!
I wouldn't be so sure about the C++ part ;)