Yeah, we have to pick *one* environment (this chooses a VM image, behind the scene, and sets a few defaults, like reporting the C++ compiler version, but nothing serious), and they have a base image shared by a number of platforms, plus a few more specific images for a subset (Java, Go, Ruby, a few others)...

The base image contains a recent-ish version of the JDK, Go, Ruby, and so on, but the specific images have multiple versions, so you can have it test your code against different versions of the JDK automatically, for example. But if you pick Java, then you can't pick Go, and so on. So I picked something that gets us the base image (it can test against gcc and Clang, FWIW).