If you're used to c#, consider using Kotlin for your Android apps.  It's got a lot of advantages over Java, including better null safety, first class property support, extension methods, and deep interoperability with existing Java.  It's also supported officially by Android and all of their future APIs will have both a Java and kotlin API review, so it's not half-assed.  

I've just successfully pushed Google internally to start supporting it, so even Google's applications should have Kotlin showing up over the next year, and fully 24% of the top 1000 play store apps use it in some capacity.

Check it out, try the kotlin koans to get familiar, and look at the Android kotlin extensions library.   All good stuff. And it should feel a bit more natural to a C# guy.