Question

List<Integer> mylist = new ArrayList<Integer>();

ArrayList<Integer> mylist2 = new ArrayList<Integer>();

I am wondering what is the actual difference between the above two in java collections API. I am new to java collections API. I know that List is an interface that ArrayList class implements.

Answer 1

In your statement 1, since you are referring mylist as List<Integer> while it is still ArrayList<Integer>, hence you can use the methods available in the List interface ONLY. This is better statement, if you are using cross class.method functionality.

Also any method accepting List<Integer> can accept any of the implementation classes of List e.g. LinkedList<Integer> or your custom implementation class.

Your second statement, creates and references the object as ArrayList<Integer> ONLY. Some people perefer it when mylist is to be used locally in the method.