Can you explain the working principle of FixedThreadPool and how it differs from other thread pools?

FixedThreadPool is a type of thread pool in Java that creates a fixed number of threads and reuses them to execute tasks. When creating a FixedThreadPool, a fixed number of threads is specified, for example:

ExecutorService executor = Executors.newFixedThreadPool(5);

Working principle:

• If a new task arrives and there is a free thread, the task is executed immediately.
• If all threads are busy, the task is placed in a queue and waits for its turn.
• Threads are not created beyond the specified number, which helps control resource usage.

Differences from other pools:

• CachedThreadPool creates new threads as needed and removes unused ones; the number of threads is not fixed.
• SingleThreadExecutor contains only one thread; tasks are executed sequentially.
• ScheduledThreadPool is designed for delayed or periodic task execution.

FixedThreadPool is useful when you need to limit the number of tasks executed simultaneously and avoid creating too many threads.