Java for OS X

Java is a programming language that allows application/software to run on different operating systems (e.g. Mac OS X, Windows, Linux, Solaris) as long as a Java Runtime Environment (RE) is installed on the target operating system. Java can also be found on web sites where "applet" code downloaded from the web site server will run locally on your computer via a web browser plug-in.

NOTE:

For the above reasons Java is a common attack vector for malware and viruses.
Java should not be confused with JavaScript which is a completely separate/different scripting language used on web sites/the internet.
Java is now owned and maintained by Oracle.

In the past (Java RE v6 and earlier) Apple used to get the Java code from Oracle and write a Java Runtime Environment (RE) for Mac OS X but as of early 2013 this is no longer the case. Java on a Mac consists of two primary software components:

An internet plug-in used to run Java "applets" via the internet in a web browser e.g. some banking web sites.
A "Runtime Environment" (RE) that also allows you to run Java "applications" directly within the operating system.

Q. How can I tell if a Java RE is installed on my Macintosh?

Go to Apple menu > System Preferences > Java (if a Java Preference pane exists you have Java RE v7 or later installed - you can get information on the version installed by going to the General tab and clicking "About…")
If you do not have a Java Preference pane go to Macintosh HD > Applications > Utilities > Terminal
Enter the following commmand:
```
sudo /usr/libexec/java_home
```
Enter your computer's administrator password
NOTE: This Terminal command will report any versions of Java RE v6 or earlier that are installed on your computer. If none are listed you do not have Java installed.

For more information on Java , check here and here