Explain FlatMap() In Java 8 Streams | How FlatMap() Works In Java 8 Streams | FlatMap | InterviewDO

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Explain FlatMap() In Java 8 Streams | How FlatMap() Works In Java 8 Streams With Example | InterviewDOT

What does the flatmap() function do? why you need it? (answer)
The flatmap function is an extension of the map function. Apart from transforming one object into another, it can also flatten it.

For example, if you have a list of the list but you want to combine all elements of lists into just one list. In this case, you can use flatMap() for flattening. At the same time, you can also transform an object like you do use map() function.

In order to understand the flatMap() method, you first need to understand the map() function of Java 8. The map() function is declared in the java.util.stream.Stream class and uses to transform one Stream into another, for example, it can convert a stream of integer numbers into another stream of ints where each element is the square of the corresponding element in the source stream. In the map() operation, a function is applied to each element of the source Stream and return values are inserted into a new Stream which is returned to the caller. The key point to note here is that the function used by map() operation returns a single value.

Now, if the map operation uses a function which instead of returning a single value returns a Stream of values like when you give a number and it returns all prime factors of the number then you have a Stream of Stream of integers. That's where flatmap function helps.

flatMap() is working fine to flatten a Stream of List of String into just a Stream of String, that's the true power of flat map operation in Java 8.

Code : https://github.com/net-vinothkumar/ILoveJavaProgramming