Java primitive array List.contains does not work as expected

Question

Why when I use this code,

int[] array = new int[3];
array[0] = 0;
array[1] = 1;
array[2] = 2;
System.out.println(Arrays.asList(array).contains(1));

it outputs false. But when I use this code,

Integer[] array = new Integer[3];
array[0] = 0;
array[1] = 1;
array[2] = 2;
System.out.println(Arrays.asList(array).contains(1));

it outputs true?

Answer 1

Arrays.asList(int[]) will return a List<int[]>, which is why the output is false.

The reason for this behavior is hidden in the signature of the Arrays.asList() method. It's

public static <T> List<T> asList(T... a)

The varargs, internally, is an array of objects (ot type T). However, int[] doesn't match this definition, which is why the int[] is considered as one single object.

Meanwhile, Integer[] can be considered as an array of objects of type T, because it comprises of objects (but not primitives).

Answer 2

Arrays.asList(array) converts an int[] to a List<int[]> having a single element (the input array). Therefore that list doesn't contain 1.

On the other hand, System.out.println(Arrays.asList(array).contains(array)); will print true for the first code snippet.