Executors returns different type of ThreadPools catering to specific need.

1. public static ExecutorService newSingleThreadExecutor()

Creates an Executor that uses a single worker thread operating off an unbounded queue

There is a difference between newFixedThreadPool(1) and newSingleThreadExecutor() as the java doc says for the latter:

> Unlike the otherwise equivalent newFixedThreadPool(1) the returned executor is guaranteed not to be reconfigurable to use additional threads.

Which means that a `newFixedThreadPool` can be reconfigured later in the program by: `((ThreadPoolExecutor) fixedThreadPool).setMaximumPoolSize(10)`

This is not possible for newSingleThreadExecutor

Use cases:

1. You want to execute the submitted tasks in a sequence.
2. You need only one Thread to handle all your request

Cons:

1. Unbounded queue is harmful

1. public static ExecutorService newFixedThreadPool(int nThreads)

Creates a thread pool that reuses a fixed number of threads operating off a shared unbounded queue. At any point, at most nThreads threads will be active processing tasks. If additional tasks are submitted when all threads are active, they will wait in the queue until a thread is available

Use cases:

1. Effective use of available cores. Configure nThreads as Runtime.getRuntime().availableProcessors()
2. When you decide that number of thread should not exceed a number in the thread pool

Cons:

1. Unbounded queue is harmful.
2. public static ExecutorService newCachedThreadPool()

Creates a thread pool that creates new threads as needed, but will reuse previously constructed threads when they are available

Use cases: