Learning RxJava - Second Edition

filter()

The filter() operator accepts Predicate<T> for a given Observable<T>. This means that you provide it a lambda that qualifies each emission by mapping it to a Boolean value, and emissions with false will not go downstream.

For instance, you can use filter() to only allow string emissions that are not five characters in length:

import io.reactivex.rxjava3.core.Observable;public class Ch3_05 {    public static void main(String[] args) {        Observable.just("Alpha", "Beta", "Gamma")              .filter(s -> s.length() != 5)              .subscribe(s -> System.out.println("RECEIVED: " + s));    }}

The output of the preceding code snippet is as follows:

RECEIVED: Beta

The filter() operator is probably the most commonly used to suppress emissions.

Note that if all emissions ...