Flat Map In Java

To put it in simple words, a map is for transformation while flatmap is a combination of transformation and flattering. The stream flatmap () method is used to flatten a stream of collections to a stream of objects. This means that the flatmap () operation first applies the map () operation, then flattens the result.

Let’s look at an example of flatmap by creating a new intellij java project and adding the rxjava dependency. A map doesn't allow duplicate keys, but you can have duplicate values. Useful methods of map interface

It does not flatten the stream.

Map function the map () method with stream api takes a function as an argument. Java's functional api supports both map() and flatmap(). Map () function produces one output for one input value, whereas flatmap () function produces an arbitrary no of values as output (ie zero or more than zero) for each input value. However, flatmap() flattens streams in addition to mapping the elements in those streams.