Java 8 features - class 27 Stream APIs - Difference between map() vs flatMap() methods and its usage

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In Java, particularly when working with streams, map() and flatMap() serve similar but distinct purposes. Here's a detailed comparison.

map()
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Functionality: Transforms each element of the stream by applying a specified function.
Return Type: Returns a new stream with the same number of elements as the original, where each element is the result of the transformation.
Use Case: Use map() when you want to apply a transformation that results in a single output for each input.

flatMap()
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Functionality: Similar to map(), but it flattens the results. It applies a function that returns a stream for each element and combines the results into a single stream.
Return Type: The resulting stream may have a different number of elements than the original, depending on the output of the transformation function.
Use Case: Use flatMap() when you want to transform each element into multiple outputs and flatten those results into a single stream.

Summary:-
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map(): Transforms each element into one element (1:1 mapping).
flatMap(): Transforms each element into zero or more elements and flattens the result (1 : many mapping).
This distinction is especially useful when dealing with collections of collections or when you need to handle optional or nullable values.

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