Example.java

Observable<String> w1 = Observable.just("Hello");
Observable<String> w2 = Observable.just("Goodbye");
Observable.zip(w1, w2, (s1, s2) -> Observable.just(s1 + " and " + s2))
  .flatMap(obs -> obs)
  .subscribe(System.out::println);

// Outputs "Hello and Goodbye"