Android was not 100% compatible with Java, but mostly because it had a specialized environment. It did not support things like dynamic bytecode generation, but it faithfully reproduced pretty much everything else that made sense.

And yeah, it would have been so much better with Oracle(tm)(r)(c)(fuckyou) running Android with Pure Java(tm)(r)(c)(screwyou) instead. Now with EJB5 and more XML!

You might be too young to remember, but SunOracle essentially abandoned the Java language development for more than a decade, until Kotlin provided a very much needed magic kick.

Oh, and if you think _Google_ is bad for splitting the Java ecosystem, let me introduce you to J2ME and JavaCard.