Java 22: Stream Gatherers

Java 22 introduces Stream Gatherers, a preview language feature, that allows you to build complex stream pipelines using custom intermediate operations, such as grouping elements based on specific criteria, selecting elements with intricate conditions, or performing sophisticated transformations. Furthermore, Stream Gatherers offer seamless integration with parallel stream processing, ensuring optimal performance even in parallel execution scenarios.

There are built-in gatherers like fold, mapConcurrent, scan, windowFixed, and windowSliding, but you can also define your own custom gatherers.

Here is an example using the windowFixed gatherer to group elements in a stream into sliding windows of a specified size:

IntStream.range(0,10)
  .boxed()
  .gather(Gatherers.windowFixed(2))
  .forEach(System.out::println);

// Result:
[0, 1]
[2, 3]
[4, 5]
[6, 7]
[8, 9]