Executors and Thread Pools

Executors and thread pools are the main boundary between application code and task execution policy in classic Java concurrency. They decide how work is queued, how many tasks run at once, and what happens under overload.

That means pool choice is an architecture decision, not a convenience detail. A fixed pool, scheduled executor, custom ThreadPoolExecutor, and virtual-thread executor all express different assumptions about workload, latency, and failure behavior.

The pages in this section focus on those choices: what the executor model actually buys you, when ExecutorService is enough, when custom tuning is justified, and how queueing policy changes the behavior of the whole system.

In this section

• Understanding Executors and Thread Pools in Java
  Understand how Java executors and thread pools separate task submission from execution policy, queueing, and overload behavior.
• Using `ExecutorService` in Java
  Use `ExecutorService` to submit, manage, and shut down concurrent Java work cleanly without leaking tasks or hiding lifecycle ownership.
• Scheduled Executors in Java
  Use scheduled executors in Java for delayed and periodic work, and choose the right scheduling mode to avoid drift, overlap, or backlog surprises.
• Custom Thread Pools in Java
  Build custom Java thread pools only when workload isolation, naming, queueing, or rejection policy needs justify more than the defaults.
• Tuning `ThreadPoolExecutor` in Java
  Tune Java `ThreadPoolExecutor` settings with queue size, pool bounds, and rejection policy aligned to real workload behavior.