Skip to main content

Deals You Can't Miss

1 Year Subscription

When do you use map vs flatMap in RxJava?

 Learning RxJava is an overwhelming exercise because it is a paradigm shift in the way you solve your coding problems. During this learning process, of the many doubts you'll have, one such would be, "When do you use map vs flatMap in RxJava?".

ProTip : Get used to understanding the Marble Diagram for understanding the basic concepts of Reactive Extensions.


Here is a simple thumb-rule that I use help me decide as when to use flatMap() over map() in Rx's Observable.

Once you come to a decision that you're going to employ a map transformation, you'd write your transformation code to return some Object right? If what you're returning as end result of your transformation is:
  • a non-observable object then you'd use just map(). And map() wraps that object in an Observable and emits it.
  • an Observable object, then you'd use flatMap(). And flatMap() unwraps the Observable, picks the returned object, wraps it with its own Observable and emits it.

Say for example we've a method titleCase(String inputParam) that returns Titled Cased String object of the input param. The return type of this method can be String or Observable<String>.
  • If the return type of titleCase(..) were to be mere String, then you'd use map(s -> titleCase(s))
  • If the return type of titleCase(..) were to be Observable<String>, then you'd use flatMap(s -> titleCase(s))

Hope that clarifies. And if this post helped you pick the concept, I'd appreciate you share the post and upvote this answer in StackOverflow. Thanks in advance :)

My Popular Posts

Ten Commandments of Egoless Programming

We are nothing but the values we carry. All through my life thus far, I tried to influence people around me with the virtues I value. Thanks to some good reading habits I had inculcated, and the fortune of being in good community of peers and mentors alike, I managed to have read some real good books. This post is about the 10 commands of egoless programming in Weinberg's book. I shall explain the commandments based on my experience here. So very many decades ago, Gerald M. Weinberg authored  The Psychology of Computer Programming . In it, he listed The Ten Commandments of  Egoless Programming , which remains relevant even today for us as not just programmers but as team-members. Weinberg is regarded as a pioneer in taking a people-centric approach to computing, and his work endures as a good guide to intelligence, skill, teamwork, and problem-solving power of a developer. When they appear to inspire and instruct, we find that they can apply to just about every business area, and e

Should I buy refurbished laptop from Amazon?

This post is based on my experience with amazon.in and guess it to be true on all other platforms as well. At least you can check out and verify for these pointers before you make that decision to buy renewed/refurbished laptop on Amazon with your hard earned money. I see this question propping up in several forums and on many different occasions. In the recent past, I had my 5 year old dell laptop that gave up because its motherboard failed. One of the options that I had in my mind was to re-use the HDD and the 16GB DDR4 RAM of that old laptop in the one that I purchase next as secondary.  I had come to a conclusion that it is not worth buying a refurbished/renewed laptop at all. Why? For the following reasons, most of which I see as BIG #RedFlags: You got to remember that Amazon provides a platform for 3rd party sellers to sell their products as well. So in your search for refurbished laptops you wouldn’t want to choose some random 3rd party seller who Amazon doesn’t endorse. You cou

Multi-tenant Architectures

  Multi-tenancy Application Deployment Architecture could be modeled in 4 broad ways: Separate Apps & Separate Databases Shared Apps & Shared Databases Separate Apps & Shared Databases Shared Apps & Separate Databases There is no right or wrong here. It's about choice and consequence that you should consider taking into your business context and constraints. In this post I intend to jot down a some key points to keep in mind for each of these multi-tenant architecture. These are more of quick notes for my quick reference, a cheat-sheet of sorts when I have to make choices. And I guess this can come handy to you too in your wise decision making. Separate Apps & Separate Databases Easiest to implement from development and deployment stand-point. Just automate the deployment infrastructure for every tenant for quick set-up. Most expensive of all the models from infrastructure cost stand-point. Relatively longer deployment t