This post explains how to install Java or check which version is running on your machine. Install on any OS, and learn about the JDK.

The JDK is the development platform for building Java applications. Learn about different JDK versions, then install a JDK in your development environment and use it to compile a Java program.

Mac OS Runtime for Java (MRJ) provides Mac users with the ability to run applets and full applications written in Java.