Java Tutorial: Concurrency
Threads, Runnable, ExecutorService, synchronized, volatile, Future, and CompletableFuture for concurrent Java programs.
Do multiple things at once
Concurrency lets your program do multiple things simultaneously — handle 1000 web requests, download files while processing existing ones, compute in parallel.
Java has excellent concurrency support — but with power comes complexity. Race conditions and deadlocks are the hardest bugs to debug. This chapter teaches you how to avoid them.
What you'll learn in this Java concurrency tutorial
This interactive Java tutorial has 6 hands-on exercises. Estimated time: 25 minutes.
- Creating threads — Two ways to create a thread:
- Race conditions — the silent enemy — When multiple threads modify shared data without synchronisation, you get incorrect results:
- synchronized — mutex lock — `synchronized` ensures only one thread enters a block at a time:
- ExecutorService — thread pools — Creating threads is expensive. A **thread pool** reuses threads:
- CompletableFuture — async pipelines — `CompletableFuture` is the modern async API — chain operations without blocking:
- Build a parallel word counter — Final challenge — no starter code.
Java Concurrency concepts covered
- Do multiple things at once