Craig Martin’s Got a PC!

[cjsiam]

I'm not an expert, by any stretch...but...

Java is a SDK (software developers kit) that is distributed and installed in a known location to all software that might use it.
Browsers use it (some, some better then others)
Programs (like vassal) use it as well...

Java is a library of functionality....
Vassal uses this library
Uber uses Vassal....
I pick up your units....
'nuf said.