遍历集合方式:

    public static void main(String[] args) {
        List<Object> arrayList = new ArrayList<>();
        arrayList.add(1);
        arrayList.add(3);
        arrayList.add(111);
        Iterator<Object> iterator = arrayList.iterator();
        while (iterator.hasNext()){
            System.out.println(iterator.next());
        }

    }

arraylist底层原理

hashset