Google Java for Mac OS X.
Remember that Apple has disabled Java, certainly in Lion and Mountain Lion, so take a look at Safari preferences, Security, and see if you have Java enabled.
Suddenly Java has disappeared from my MacBook Pro. I don't know how to get it back. I tried all the tips given but it is still gone. When I click on "utilities", then "other", and the only thing listed is Flash. When I look to see if Java is enabled, etc., it says it is. I'm defeated. HELP! The operating system is 10.6 and I've used Java for months - no idea why it's gone.