将Arrays.asList与int数组一起使用

Question

Using java.util.Arrays.asList , why its shows different list size for int (Primitive type) and String array?

a) With int array, whenever I execute following program the List size = 1

public static void main(String[] args) {
        int ar[]=new int[]{1,2,3,4,5};
        List list=Arrays.asList(ar);
        System.out.println(list.size());

    }

b) But if i change from int array type to String array(like String ar[] = new String[]{"abc","klm","xyz","pqr"}; ) , then I am getting the list size as 4 which i think is correct.

PS : With Integer (Wrapper Class) array, then result is Fine, but i am not sure why in primitive int array, the list size is 1. Please explain.

Answer 1

List cannot hold primitive values because of java generics (see similar question ). So when you call Arrays.asList(ar) the Arrays creates a list with exactly one item - the int array ar .

EDIT:

Result of Arrays.asList(ar) will be a List<int[]> , NOT List<int> and it will hold one item which is the array of int s:

[ [1,2,3,4,5] ]

You cannot access the primitive int s from the list itself. You would have to access it like this:

list.get(0).get(0) // returns 1
list.get(0).get(1) // returns 2
...

And I think that's not what you wanted.

Answer 2

List is a generic type, primitive types are not valid substitutes for the type parameter.

So in your first example when you call Arrays.asList() with an int[] , the value for the type parameter will be int[] and not int , and it will return a list of int arrays. It will have only 1 element, the array itself.

The second case will be a List<String> , properly holding the 4 strings which you pass to it.