java.util.concurrent: Executors, Thread Pools(Cache, Fixed, Scheduled), ExecutorCompletionService – A tutorial

I received a request from one of my blog readers Kunal inquiring if I was planning to post something on FutureTask and ExecutorCompletionService. Since he put the seed of a possible blog post in my mind, I decided to go ahead and write a post on the two concurrency classes. Additionally to make the coverage complete the post intends to cover the Executors class as well.