I'm going to be honest, this is not my area of expertise, but no one seems to have responded, so I'll see if I can help you in any way. If you have the Java Development Kit (JDK) you should be able to use the pure java version (Download). From what google tells me, it seems there are some third party softwares that allow you to get it. Unfortunately, there does not seem to be a dedicated release of greenfoot for Arch. Sorry.