Difference between Arrays asList array and new ArrayList Integer Arrays asList array

Question

What's the difference in these two ways?

1. List<Integer> list1 = new ArrayList<Integer>(Arrays.asList(ia));
2. List<Integer> list2 = Arrays.asList(ia);

Note that ia refers to integer array

I have come to find that some operations are not allowed for list2. Why is that the case? How does it get stored into the memory?

If I shuffle lists, ist1 doesn't change the original array, but list2 does. So list2 is confusing for me.

How does the ArrayList being upcasted to list is different than creating a new ArrayList?

list1 differs from (1)
ArrayList<Integer> list1 = new ArrayList<Integer>(Arrays.asList(ia));