Java / Java8 streams
Difference between map and flatmap in Java.
In Java streams, the primary difference is that map() performs a one-to-one transformation, returning a stream of the same size as the input, while flatMap() handles one-to-many transformations and flattens nested data structures into a single-level stream.
| Parameter | map() | flatMap() |
|---|---|---|
| Mapping | One element to one element. | One element to zero or many elements. |
| Function Return Type | Returns a single value (R) for each input (T). | The function itself returns a Stream<R> (or Optional<R>, etc.) for each input (T). |
| Output Structure | Keeps the nested structure (e.g., Stream<List<R>>). | Flattens the structure into a single level (e.g., Stream<R>). |
| Purpose | Used only for transformation of elements. | Used for both transformation and flattening. |
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