StudyToCert

All certifications / OCP Java / Lessons

Oracle Certified Professional: Java SE Developer 1Z0-831 (Java SE 25) · Domain 6: Working with streams and lambda expressions

Parallel streams and why stateful lambdas cause problems

▶ Watch the overview video

Last reviewed September 25, 2026 · Leer en español

A parallel stream splits its source into parts and processes them on several threads at once, then combines the results. You get one by calling parallelStream() on a collection or parallel() on an existing stream; sequential() switches back, and isParallel() tells you the mode. Because the whole pipeline has a single mode, the last parallel() or sequential() call wins. By default the work runs in the common ForkJoinPool.

Free account

Keep reading for free

Create a free StudyToCert account to read the rest of this lesson: 5 more sections, 4 key terms, a real-world example, an exam tip and self-check questions. Every lesson, lab and practice test is free with an account.

Sign up free Log in

Study OCP Java for free
A week-by-week plan with every lesson, quizzes, checkpoint tests, a practice exam and hands-on labs.
Open the OCP Java study plan