It has limitations on runtime introspection and modification, but once you learn them, you can use idiomatic java and/or scala. That said, the limitations make it difficult to easily port.

The only limitation is the lack of runtime byte code genration. Reflection and proxies work as intended.

One big positive is that it uses the same class libraries as Android, so if you're already targeting Android and not using runtime code generation, you don't have to port any of your non-UI code.