There's a whole section in that opinion I linked above titled, "Google's Interoperability Arguments are Irrelevant to Copyrightability," that's worth reading for a deeper treatment of the issue. In particular, Judge O'Malley (quite reasonably) calls bullshit on the very premise that Google copied the Java APIs in order to achieve interoperability, pointing out that Google did specific things to prevent such interoperability (as an aside, we now know that their desire to do so, and Sun's unwillingness to agree to that, is a major reason why they could not come to terms on a licensing agreement), and was unable to produce any examples of a pre-existing Java program that also runs on Android.