Learning RxJava

toMap() and toMultiMap()

For a given Observable<T>, the toMap() operator will collect emissions into Map<K,T>, where K is the key type derived off a lambda Function<T,K> argument producing the key for each emission.

If we want to collect strings into Map<Char,String>, where each string is keyed off their first character, we can do it like this:

import io.reactivex.Observable;public class Launcher {      public static void main(String[] args) {        Observable.just("Alpha", "Beta", "Gamma", "Delta", "Epsilon")          .toMap(s -> s.charAt(0))          .subscribe(s -> System.out.println("Received: " + s));      }}

The output of the preceding code snippet is as follows:

    Received: {A=Alpha, B=Beta, D=Delta, E=Epsilon, G=Gamma}

The s -> s.charAt(0) lambda argument takes each ...