RxJava - Creating Observables

Following are the base classes to create observables.

Flowable − 0..N flows, Emits 0 or n items. Supports Reactive-Streams and back-pressure.

Observable − 0..N flows ,but no back-pressure.

Single − 1 item or error. Can be treated as a reactive version of method call.

Completable − No item emitted. Used as a signal for completion or error. Can be treated as a reactive version of Runnable.

MayBe − Either No item or 1 item emitted. Can be treated as a reactive version of Optional.

Following are the convenient methods to create observables in Observable class.

just(T item) − Returns an Observable that signals the given (constant reference) item and then completes.

fromIterable(Iterable source) − Converts an Iterable sequence into an ObservableSource that emits the items in the sequence.

fromArray(T... items) − Converts an Array into an ObservableSource that emits the items in the Array.

fromCallable(Callable suppper) − Returns an Observable that, when an observer subscribes to it, invokes a function you specify and then emits the value returned from that function.

fromFuture(Future future) − Converts a Future into an ObservableSource.

interval(long initialDelay, long period, TimeUnit unit) − Returns an Observable that emits a 0L after the initialDelay and ever increasing numbers after each period of time thereafter.