java collections vs map in collections framework

Question

According to http://docs.oracle.com/javase/tutorial/collections/interfaces/index.html there are two top level interfaces called collection and map.

Whats the exact reason for separating these two ?

Is it that all key value data structures implement the map interface and all others implement the collections interface ?

Answer 1

Yes, That's correct! Check all the List classes and then check all the Map related classes.

and there is this awesome discussion, ob this question

List vs Map in Java

Visually

This is a collection, by this you know that the books are there and it's in order like 0,1,2,3...

But in a Map, the books are in memory unordered but for the computer's convenience it has a key to find the books, like in a library.

Answer 2

A Map is a structure that has unique keys mapping to values. A Collection is just a grouping of multiple values with no specific key.

You can do the same comparison between a List and a Map to see the differences. This SO question deals with these differences.