Converting Array to List

The second one creates a new array of Integers (first pass), and then adds all the elements of this new array to the list (second pass). It will thus be less efficient than the first one, which makes a single pass and doesn't create an unnecessary array of Integers.

A better way to use streams would be

List<Integer> list = Arrays.stream(ints).boxed().collect(Collectors.toList());

Which should have roughly the same performance as the first one.

Note that for such a small array, there won't be any significant difference. You should try to write correct, readable, maintainable code instead of focusing on performance.

Simply try something like

Arrays.asList(array)

If you don't want to alter the list:

List<Integer> list = Arrays.asList(array)

But if you want to modify it then you can use this:

List<Integer> list = new ArrayList<Integer>(Arrays.asList(ints));

Or just use java8 like the following:

List<Integer> list = Arrays.stream(ints).collect(Collectors.toList());

Java9 has introduced this method:

List<Integer> list = List.of(ints);

However, this will return an immutable list that you can't add to.

You need to do the following to make it mutable:

List<Integer> list = new ArrayList<Integer>(List.of(ints));