Java:programmer's Boon

DIFFERENCE BETWEEN HASHMAP AND HASHTABLE PLEASE COMMENT

Collections.sort() uses merge sort and arrays.sort() uses quick sort...
For primitive type quick sort is efficient...and for non primitives merge sort is more efficient .
why a different sort algorithm is used for primitive arrays than for Object arrays?

Since the introduction of Functional programming in Java 8 , it has brought new concepts and flexibility for the language.

So what is functional programming?
How it is different from object oriented programming ?
When do we need functional programming ?

Let's have some discussion on this. Please post your answers in the comments section.