Java Parallel Streams Internals: Combining Results Part 1

This video explores the internals of Java parallel streams, focusing on how results are combined in the final phase of the split-apply-combine model. I distinguish between the reduce() and collect() terminal operations, elaborating that reduce() expects immutable objects and creates a new value by applying a given function to each subset of data. Conversely, collect() works with mutable result containers, such as TreeSet and HashSet, and performs localized collections before merging them. This presentation also highlights that non-concurrent collectors handle the merging and synchronization, negating the need for manual locking. Finally, I outline the concept of concurrent collectors, which use a single, thread-safe mutable container that potentially improves performance.