Question

What is best way recopying int[] array elements into ArrayList?

I need to do this fast so what would be the fastest way?

Answer 1

Use Arrays#asList(T... a) to create “a fixed-size list backed by the specified array. (Changes to the returned list “write through” to the array.)”

Integer[] intArray = {1, 2, 3, 42}; // cannot use int[] here
List<Integer> intList = Arrays.asList(intArray);

Alternatively, to decouple the two data structures:

List<Integer> intList = new ArrayList<Integer>(intArray.length);

for (int i=0; i<intArray.length; i++)
{
    intList.add(intArray[i]);
}

Or even more tersely:

List<Integer> intList = new ArrayList<Integer>(Arrays.asList(intArray));