Parallel Streams Basics
Learn the basics of parallel streams and when to use them.
Parallel Streams Basics is a free Java Academy lesson on CoddyKit — lesson 2 of 3. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Java Academy learning path, one of 3 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Intro
Parallel streams split work across multiple threads to use multi-core CPUs.
Create
Use parallelStream() on a collection or call parallel() on a Stream.
Code: parallel stream
This shows multiple threads processing elements in parallel.
import java.util.*;public class Main {
public static void main(String[] args) {
List<Integer> nums = Arrays.asList(1,2,3,4,5);
nums.parallelStream().forEach(n -> System.out.println(Thread.currentThread().getName() + " processed " + n));
}
}
Ordering
Parallel streams may process elements out of order. Use forEachOrdered if order matters.
Code: forEachOrdered
forEachOrdered restores encounter order in parallel streams.
import java.util.*;public class Main {
public static void main(String[] args) {
List<Integer> nums = Arrays.asList(1,2,3,4,5);
nums.parallelStream().forEachOrdered(System.out::println);
}
}
Performance
Parallel streams help with CPU-bound tasks on large collections but may be slower for small ones due to overhead.
Parallel streams check
Quick check: What is one risk of using parallel streams?
Recap
Recap: Parallel streams use multiple threads. They are best for large CPU-bound tasks, not for small ones.
Frequently asked questions
Is the “Parallel Streams Basics” lesson free?
Yes — the full text of “Parallel Streams Basics” is free to read here on the web, and the Java Academy course includes 3 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Java Academy course, upgrade to CoddyKit PRO.
What will I learn in “Parallel Streams Basics”?
Learn the basics of parallel streams and when to use them. You practise Java Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Java Academy?
No prior experience is required. Java Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 2 of 3, so you can start here or from the beginning and move at your own pace.
How long does the “Parallel Streams Basics” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Java Academy lesson?
Yes. Every Java Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Ordering & Short-circuiting
- Parallel Streams Basics
- Common Pitfalls