Significance arraylist argument in java

<pre>List<Integer> l=new ArrayList<>();
       l.add(1);
       l.add(2);
       l.add(3);
       l.add(4);
       System.out.println("Element at 0th index: "+l.get(0));
       Iterator i=l.iterator();
        while(i.hasNext())
        {
            Integer obj=(Integer)(i.next());
            int o=obj;
            System.out.println(o);
        }

Element at 0th index: 1
1
2
3
4

<pre lang="java"><pre>List<Integer> l=new ArrayList<>();

<pre><pre lang="java"><pre>List<Integer> l=new ArrayList<>(2);