I'm too! I don't program in Java but I've never read that the compiler or JVM can do anything like that automatically (making the user's code running in parallel even if the user didn't specify anything).
I suspect that what he observes is the garbage collector running on more cores at once (AFAIK it is designed to run so now) and that the garbage collection was the cause of the slowness in Go too. I persume he managed to have a heck a lot of allocatations and that caused the slowness of Go and the full-throttle GC run in Java. But this is just a guess. If anybody knows more exact details please write!
