Different between Map and FlatMap in RX

In short, the map applies a function to each emitted element and returns its result.

Observable<Integer> observable = Observable
        .just(1,2,3)
        .map(x -> 10 * x);

observable.subscribe(System.out::println);Result:
10
20
30

So FlatMap applies a function to each emitted element, but this function returns the type of the Observable. I.e. 1 emitted by an element through a flatMap to generate a set of emitted elements or not one.

Observable<String> observable = Observable
        .just("A", "B", "C")
        .flatMap(s -> {
            System.out.println();
            return Observable.just(s + "1", s + "2", s + "3");

        });

observable.subscribe(s -> System.out.print(s + " "));
Result:A1 A2 A3 
B1 B2 B3 
C1 C2 C3