Generics have unexpected behaior using primitives array instead of wrapper array

Question

The following code is returning a List of Integer:

Integer[] arr = new Integer[] {3,2,1};
List<Integer> list = Arrays.asList(arr);

Why is the same code using "int" returning a List of int[]:

int[] arr = new int[] {3,2,1};
List<int[]> list = Arrays.asList(arr);

very-close-to-duplicate: stackoverflow.com/questions/26814064/… — yshavit
– yshavit, Commented Nov 12, 2014 at 17:36

Jon Skeet · Accepted Answer · 2014-11-12 17:33:15Z

3

Yes, it's treating that as a call using varargs and int[] as the type argument, i.e.

List<int[]> list = Arrays.<int[]>asList(new int[][] { arr });

The alternative would be to infer T=int... which is impossible, as Java generics don't support the use of primitive as type arguments. That restriction is the reason for the difference here.

answered Nov 12, 2014 at 17:33

Jon Skeet

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