Learning RxJava - Second Edition

switchIfEmpty()

Similar to defaultIfEmpty(), switchIfEmpty() specifies a different Observable to emit values from if the source Observable is empty. This allows you to specify a different sequence of emissions in the event that the source is empty rather than emitting just one value, as in the case of defaultIfEmpty().

We could choose to emit three additional strings, for example, if the preceding Observable came out empty due to a filter() operation:

import io.reactivex.rxjava3.core.Observable;public class Ch3_04 {    public static void main(String[] args) {        Observable.just("Alpha", "Beta", "Gamma")             .filter(s -> s.startsWith("Z"))             .switchIfEmpty(Observable.just("Zeta", "Eta", "Theta"))             .subscribe(i -> System.out.println("RECEIVED: " + i),