How to check for and disable Java in OS X

There's some concern over the use of Java in OS X following a recent finding that Flashback malware variants are now taking advantage of currently unpatched vulnerabilities in the Java runtime.

Even though this malware development should not affect the majority of Mac users running OS X 10.7 or later since Apple no longer includes Java with the OS, some people may nonetheless be wondering what the Java runtime is, and how they can go about checking for and removing it from their systems to ensure they are safe.