Stream Gatherers

Introduced in Java 22, Stream Gatherers define a way to customize intermediate stream operations, allowing developers to manipulate data flows dynamically.

Built-in Gatherers

Java 22 provides several pre-configured gatherers:

• Gatherers.windowFixed(size): Groups stream elements into fixed-size lists (batches).
• Gatherers.windowSliding(size): Groups stream elements into sliding windows.
• Gatherers.fold(initializer, accumulator): Stateful reduction mapping to a single value.

Code Walkthrough

This program demonstrates grouping stream elements into fixed-size windows.

import java.util.List;
import java.util.stream.Gatherers;
import java.util.stream.Stream;
public class StreamGathererDemo {
    public static void main(String[] args) {
        List> batches = Stream.of(1, 2, 3, 4, 5, 6, 7, 8)
                .gather(Gatherers.windowFixed(3)) // Groups elements in batches of 3
                .toList();
System.out.println(batches); // [[1, 2, 3], [4, 5, 6], [7, 8]]
    }
}

Interview-Relevant Information