Asynchronous Android Programming - Second Edition

Creating Observables

To create an Observable, we can either create an Observable from scratch using the create function and calling Observer methods explicitly, or we can use built-in Observable creation methods that convert common data types to Observable streams.

Let's start with a simple example and create an observable that emits a String using the creating Observable.from operator:

Observable<String> myObservable =
  Observable.from(Arrays.asList("Hello from RxJava",
                                "Welcome...",
                                "Goodbye"));

The Observable.from static function creates Observable from an array that will synchronously emit String items to any Observer. The Observable created will be a cold Observable and will only start emitting events after an Observer subscribes to it.

Now, let's ...