Learning RxJava

count()

The simplest operator to consolidate emissions into a single one is count(). It will count the number of emissions and emit through a Single once onComplete() is called, shown as follows:

import io.reactivex.Observable;public class Launcher {      public static void main(String[] args) {        Observable.just("Alpha", "Beta", "Gamma", "Delta", "Epsilon")          .count()          .subscribe(s -> System.out.println("Received: " + s));      }}

The output of the preceding code snippet is as follows:

    Received: 5

Like most reduction operators, this should not be used on an infinite Observable. It will hang up and work infinitely, never emitting a count or calling onComplete(). You should consider using scan() to emit a rolling count instead.