Hmm, my Terminal says the command "java" is know.
In the Synaptic-Package-Manager (an all-in-one tool to get programs of any kind on Ubuntu, very important for updates) I looked up java and I found this:
Synaptic wrote:
The Java(TM) Plug-in, Java SE 6
Java Plug-in enables applets written to the Java Platform 6 specification to be run in Mozilla and other web browsers.
Java Plug-in comes with the Java Runtime Environment (JRE).
This is a metapackage containing dependencies for running Java in various browsers.
Oh yes, some librarys were there, too. My dad said that is what I need for Java scripts, even when the description says "webbrowsers".
Maybe I should move my question to UbuntuUsers.de.