Usually when someone on Oracle's side brings up compatibility, they are referring indirectly to the test suite required for using the Java trademarks. And they

Usually when someone on Oracle's side brings up compatibility, they are referring indirectly to the test suite required for using the Java trademarks. And they usually are also implying that compatibility should be defined solely by Sun/Oracle, ie. that Oracle should be allowed to require your own Java implementation to be fully functional and 100% compliant to their spec before it is in any way legal, and implementing a mere subset of relevant functionality is not permissible.