There are three, seamlessly similar operators in RxJava 2.x: flatMap(), concatMap() and concatMapEager(). All of them accept the same argument – a function from original stream’s individual item to a (sub-)stream of arbitrary type. In other words if you have a Flowable you provide a function from T to Flowable for arbitrary R type. After applying any of these operators you end up with Flowable. So how are ...