Dive deep into Stream Gatherers, a powerful API finalized in JEP 485 for Java 24, in this 43-minute conference talk presented by Viktor Klang, Software Architect from Oracle's Java Platform Group at JavaOne 2025. Learn how to create custom intermediate operations for java.util.stream.Stream when the existing operations don't meet your needs. Explore the anatomy of Java Streams, understand the evolution of the API, and see how Gatherers compare to Collectors. Follow along with practical examples showing how to implement map, mapMulti, and limit operations as Gatherers, and understand the differences between sequential and parallel evaluation. The presentation covers available Gatherers in the java.util.stream package, composition techniques, and concludes with a Q&A session. Perfect for Java developers looking to enhance their stream processing capabilities with custom transformations.
Overview
Syllabus
• 00:00 Intro
• 00:22 Java Stream Anatomy
• 02:03 Intermediate Stream Operation?
• 02:28 Growing an API
• 09:08 Evaluating Collector against the requirements
• 10:29 Stream Gatherers
• 12:37 Gatherers vs. Collectors
• 15:20 Example - Stream::map as a Gatherer
• 17:20 Example - Stream::mapMulti as a Gatherer
• 18:08 Example - Stream::limit as a Gatherer
• 21:21 Sequential vs. Parallel Evaluation
• 29:16 Some of the available java.util.stream.Gatherers
• 33:25 A note on composition
• 35:44 Conclusions
• 36:45 Q&A
Taught by
Java
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