Using Arrays.asList with int array

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.

Probably your compiler even gave you a raw type warning on List. Many IDEs will present a couple of useful fixes, one of them changing List to List<int[]>. The latter pointing you towards the answers of "daerin" and "icza". — Hille
– Hille, Commented Aug 25, 2014 at 10:45

Community · Accepted Answer · 2017-05-23 11:57:42Z

5

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 ints:

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

You cannot access the primitive ints 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.

edited May 23, 2017 at 11:57

CommunityBot

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answered Aug 25, 2014 at 10:32

daerin

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3 Comments

Arun Kumar Over a year ago

So If the Arrays creates a list with exactly one item -the int array ar then how to traverse and access that primitive values from it using list?

Arun Kumar Over a year ago

Got it! It should be like int ab[]=(int[]) list.get(0);

Arun Kumar Over a year ago

Watch carefully! list.get(0).get(0) wouldn't be accessible directly here as last get() is undefined until and unless you typecast the whole statement to some other collection (that have get method)

icza · Accepted Answer · 2014-08-25 10:32:39Z

1

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.

answered Aug 25, 2014 at 10:32

icza

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