That's what Apache created in the Harmony project. And Oracle is suing Google over that very same thing. Oracle claims that they own the copyright on Java API

That's what Apache created in the Harmony project. And Oracle is suing Google over that very same thing. Oracle claims that they own the copyright on Java API, including clean-room reimplementations of the Java API. It's a novel legal theory that didn't work for IBM or AT&T so we'll have to wait and see what happens. Oracle also has patents that pretty much prohibit anyone from writing any kind of JIT VM. That's just one more pathology of a system that allows software patents at all. It's literally illegal today to write any kind of software in the USA because of the breathtaking quantity of basic techniques patented long after their first use by our broken patent office. Oracle is just the one seeking to enforce that prohibition today.