Indeed, but as @Abuse mentions, the fact that a de facto standard implementation exists that everyone actually codes to in practice means that a clean room implementation, well, simply introduced more fragmentation and bugs than reduced them. It was with hindsight and the best of intentions, a bad idea. The long and the short of it is, Sun should have fully opened the java.* packages and plonked an appropriate license on them such that anyone could use them for anything, and left the real licensing behind the sun.* packages and the actual Hotspot native binaries.
Cas