While trying to set my java-system-vm for the first time, java-config was giving me an error. I read the man page with no luch and then went ad looked over the script. I noticed that java-config gives an error and exits if JAVA_HOME is not set. This seems a bit odd as it makes it hard to setup your initial java enviroment as I was trying to do. I assume either JAVA_HOME should be set by default to the blackdown jdk or the documentation should be updated to note that you need to set JAVA_HOME to an existing JDK before trying to use java-config to set the system-vm, etc?
It doesn't actually fail, it just emits a warning. However, this warning has now been removed so not as confuse new users. Available as dev-java/java-config-0.2.3
I actually couldn't set the system-vm until set my JAVA_HOME.