I check what java I have by this way: https://service.parachat.com/knowledgebase/211/How-do-I-check-which-Java-version -is-installed-on-my-Mac.html
java version "1.6.0_43"
Java(TM) SE Runtime Environment (build 1.6.0_43-b01-447-11M4203)
Java HotSpot(TM) 64-Bit Server VM (build 20.14-b01-447, mixed mode)
If you have Java Version 7_17 go to System Preferences > Java > Java Control Panel > Security and be sure "enable Java content in the browser" is check marked.
EDIT: Actually, Apple has disabled Java due to security issues, so run it at your own risk and only if you need it.