[pjmlp]

The Java language specification does not define how threads are implemented.

The first set of JVMs did implement green threads, which are what goroutines are. Shortly thereafter most of them switched to red threads, aka real threads.

You can still find a few JVMs that use green threads, like Squawk.

https://java.net/projects/squawk/pages/SquawkDesign

Other than that, java.util.concurrent provides mechanisms to map multiple tasks to single OS threads.