need to have Java 6 or Java 7 (also known as JDK6/JDK7) installed on your system. Get it here:
Note that only the version
labeled JDK will work. Not the one labeled JRE,
nor the one that comes with NetBeans, nor the EE version.
Debian/Ubuntu users should install the JDK via the package management system rather than using the links above. See the installation instructions.
Details about system
requirements are here.
On MacOS X 10.5+, a
recent Java SDK version is installed by default. You
do not normally need to install Java on this system,
however you should ensure that you have the latest
Java updates from Software Update.
See here for more information.