Oracle's newly released Java 7 runtime is relatively painless to install and uninstall.

You can check which Java version is on your Mac to see if you have the most up-to-date Java running, or you can check on the Java website.

Java used to be deeply embedded in OS X, but in recent versions of the OS it's an optional install. Here is how to check to see if it is installed, and how to disable or remove it.