Learning RxJava - Second Edition

count()

The count() operator counts the number of emitted items and emits the result through a Single once onComplete() is called. Here is an example:

import io.reactivex.rxjava3.core.Observable;public class Ch3_22 {    public static void main(String[] args) {        Observable.just("Alpha", "Beta", "Gamma")              .count()              .subscribe(s -> System.out.println("Received: " + s));    }}

The output of the preceding code snippet is as follows:

Received: 3

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