[needusername]

Right, you have to buy and pass the test suites (TCK).

The thing with Android is they are not close passing the test suites (AFAIK Harmony was close but Android is only a fraction of Harmony).

Compare what Android implements: http://developer.android.com/reference/packages.html And what they would have to implement: http://docs.oracle.com/javase/6/docs/api/ Of course the difference is even bigger for newer Java Versions (NIO.2, Date Time API, Fork-Join, …).

In addition I believe the linking semantics in Dalvik are slightly than in Java, eg. slf4j needs a special version to not fail during dex translation.

I'm not sure whether there is actually an official Java implementation that does not have a license of the implementation from Sun/Oracle or uses OpenJDK. If not they would have to reimplement all of the classes including AWT/Swing. Azul for example does have a license for Zing. I'm not sure if IBM already builds on OpenJDK.