What implementations of the ExecutorService interface do you know, and how do they differ?

ExecutorService is an interface for managing a thread pool and executing tasks asynchronously. The main implementations from the Java standard library:

• ThreadPoolExecutor — the most flexible and commonly used implementation, allows configuring the pool size, task queue, and overload handling policy.
• ScheduledThreadPoolExecutor — an extension of ThreadPoolExecutor, supports scheduling tasks with delay or periodic execution.
• ForkJoinPool — designed for tasks that can be broken down into subtasks (used in the Fork/Join framework), effective for parallel computations.

Differences:

• ThreadPoolExecutor is suitable for general purposes.
• ScheduledThreadPoolExecutor — for timer-based tasks.
• ForkJoinPool — for recursive parallelism.

Example of creating a ThreadPoolExecutor:

ExecutorService executor = Executors.newFixedThreadPool(4);
executor.submit(() -> System.out.println("Task completed"));
executor.shutdown();