We've written about RxJava and Android before, but this tutorial from howrobotswork takes a more in-depth look at RxJava through one particular use case: managing async API calls. If you're not familiar with RxJava, howrobotswork describes it as a "Java implementation of Reactive Extensions developed by Netflix" for asynchronous and event-based programs.
The howrobotswork tutorial provides some background and set-up, but mostly focuses on how to build an Android REST API client with RxJava observables. Any Android developers looking to get deeper into RxJava should take a look at the full tutorial. Also, it's the first part in a series, and the second part - error handling with RxJava - has already been posted, potentially with more to come.