ArrayList, Loop and requisite if can not work that i want - Java 11

I have a problem comparing the number in the list so that it does not repeat using Random. I wanted the numbers to be random, but only those that are not on the list can be added. it is my code.:

List<Integer> list = new ArrayList<>();
    int maxPosition = 5;
    private void addToListNumber() {
        int randomPosition = new Random().nextInt(5);
                if (list.size() < 1) {
            list.add(1);
            addToListNumber();
        } else if (list.size() < maxPosition) {

            list.add(randomPosition);
            addToListNumber();
        } else {

            for (Integer integer : list) {
                System.out.println(integer);
            }
        }
    }

Nevertheless the numbers repeat .. Maybe somebody explain why... I spent four hours on it and I can't figure out why the IF loop is passing the same number.

I'm sorry that my English is not perfect.