Gatherers

In Java, the Stream API provides a powerful way to process sequences of elements in a functional style. One of the key components of this API is the concept of gatherers, which are used to collect the results of stream operations into various data structures.

Martin Fowler - “Functional Programming is about building software by composing pure functions, avoiding shared state, mutable data, and side-effects.”

Collection Pipeline Pattern: A pipeline of functions through which data flows and gets transformed.

1. Source: A data source (like a Collection, array, or I/O channel)
2. Intermediate Operations: Transformations that produce a new stream (like filter, map, sorted)
3. Terminal Operation: Produces a result or side-effect (like collect, forEach, reduce)

Imperative style programming has higher accidental complexity due to managing state and control flow,

• while functional programming emphasizes declarative constructs that express the logic of computation without describing its control flow.

data -> Stage1 -> Stage2 -> ... -> StageN -> Terminal Operation

Gatherer represents a stage

Common Gatherers in Java Streams

Fold() - takes in reduce function and an initial value, and combines all elements of the stream into a single result.

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