Why do we first declare subtypes as their supertype before we instantiate them?

Question

Reading other people\'s code, I\'ve seen a lot of:

List ints = new ArrayList();
Map map = new HashMap();

Answer 1

It is just easier to think of String as of String. As well as it's easier (and more beneficial) to think of WhateverList as of List.

The bonuses are discussed many times, but in brief you simply separate the concerns: when you need a CharSequence, you use it. It's highly unlikely that you need ArrayList only: usually, any List will do.