BoxFileVersion CLASS doesn't seem to have a method to get the name of the version ("V1", "V2" etc).
I can see that BoxFile.Info has a getVersionNumber() method but this just returns a null.
BoxFile.Info.getVersionNumber()
will give you the version number, but this attribute is not populated by default - it's listed in italics in Box API docs.
Optional attributes need to be requested explicitly, e.g. by calling BoxFile.getInfo(fields)
with "version_number" in fields
array.