The examples translate Go idioms directly to Java code rather than using Java idioms; you wouldn't normally write Java like Go any more than you'd write Go like Java.

They also make use of constructs that are overkill for such simple examples. For example, the first example could be written as:

   Thread.startVirtualThread(() -> say("world"));
   say("hello");

which would also replicate same concurrency bug as in the original Go program (the Java example, as written, does not have that bug, but neither would

   var t = Thread.startVirtualThread(() -> say("world"));
   say("hello");
   t.join();

).

Go makes certain concurrency bugs easy to introduce and hard to find, while Java helps avoid them, but that is also not easy to see from these particular examples.