Why hashMap is not the part of collection framework

Question

why hashMap is not the part of collection framework ??
why Map start its own new hierarchy??
thanks

Answer 1

A Map is not simply a collection of stuff, it is a mapping from stuff to stuff.
It doesn't make any sense to "add stuff to a map", unless you tell it both a key and a value.
It doesn't make any sense to ask "does this contain stuff", unless you tell it to look in its keys or in its values.
Those (and similar) reason explain why a Map is not a Collection.
Note that there are views of the keys and the values that do behave like Collections (for example you can take the keys() view of the Map and tell it to remove stuff from it and it will do what you'd expect). But the Map as a whole is not a Collection of stuff. It is a mapping of stuff.
(I hereby declare "stuff" to be a technical term).