[mike_hearn]

The latter is not correct. You can do it and people have.

[premium-concern]

That's wrong. Feel free to present an example.

[mike_hearn]

Android is one obvious example. GNU Classpath is another. Avian is another.

[premium-concern]

Sorry, but no. None of them can passed the JCK, which is a requirement to certify a Java implementation.

[mike_hearn]

Your original statement was you can't BUILD an implementation without getting Oracle's blessing. Now you've switched to saying you can't CERTIFY which is a different claim.

[premium-concern]

I understand that you are trying to play semantics here, but in this case it doesn't work.

You can't BUILD an implementation of Java, because "Java" is defined by "passes the Java conformance tests".

You can build "something", but it won't be Java, so don't call it Java. Even Google understood that.