Learning RxJava

Single

Single<T> is essentially an Observable<T> that will only emit one item. It works just like an Observable, but it is limited only to operators that make sense for a single emission. It has its own SingleObserver interface as well:

    interface SingleObserver<T> {    void onSubscribe(Disposable d);    void onSuccess(T value);    void onError(Throwable error);    }

The onSuccess() essentially consolidates onNext() and onComplete() into a single event that accepts the one emission. When you call subscribe() against a Single, you provide the lambdas for onSuccess() as well as an optional onError():

    import io.reactivex.Single;    public class Launcher {          public static void main(String[] args) {        Single.just("Hello")          .map(String::length)          .subscribe(System ...