In order to run Java programs or applets, you must have a Java run time environment (JRE) installed. To run Java web applets in your browser, you additionally need a plugin for your browser, which is not installed by default.
If you don't have the partner repositories enabled follow these instructions first:
1. Go to System -> Administration -> Software Sources -> Other Software
2. Enable the "partner repositories"
3. Clone and if prompted about out of date software select Reload
4. Now download & install
5. Restart the browser
Website: