When multiple threads work simultaneously in a multithreaded application, do they use a shared thread pool or each have their own?

In Java, multithreaded applications can use either a shared thread pool or create separate pools for different tasks, depending on the architecture and requirements. Typically, a thread pool (ThreadPoolExecutor or Executors) is used to manage threads, which allows reusing a limited number of threads to execute multiple tasks, saving resources and increasing performance.

When multiple threads operate simultaneously, they usually take threads from a common pool rather than creating their own. This helps avoid the overhead of creating and destroying threads. However, in some cases, separate pools can be created for different types of tasks to isolate their execution.

Example of creating a shared thread pool:

ExecutorService executor = Executors.newFixedThreadPool(5);
executor.submit(() -> {
    // task
});
executor.shutdown();