Question

While doing simple program I noticed this issue.

int[] example = new int[10];
List<Integer> exampleList = Arrays.asList(example);// Compilation error here  

Compilation error is returned as cannot convert from List<int[]> to List<Integer>. But List<int> is not permitted in java so why this kind of compilation error?

I am not questioning about autoboxing here I just wondered how Arrays.asList can return List<int[]>.

asList implementation is

public static <T> List<T> asList(T... a) {
return new ArrayList<T>(a);
}

So it is treating int[] as T that is why this is happening.

Answer 1

There is no automatic autoboxing done of the underlying ints in Arrays.asList.

• int[] is actually an object, not a primitive.

• Here Arrays.asList(example) returns List<int[]>. List<int> is indeed invalid syntax.

• You could use:

  List<Integer> exampleList = Arrays.asList(ArrayUtils.toObject(array));

  using Apache Commons ArrayUtils.