ArrayList internal working

Question

I wanna test how the indexing work in case of arrayList. When I try to add element at a specified index say arrlist.add(15, "shreyas"); I get an Exception "IndexOutOfBoundException".. why is that so?? I am confused. please help..!!! Thanks in advance

ArrayList <String> arrlist = new ArrayList <String>(20);
          arrlist.add(15, "shreyas");
          arrlist.add(18, "jp");

          for(int i=0;i<arrlist.size();i++){
                 System.out.println("Index is i="+i+" And Element is "+arrlist.get(i));
   }

Answer 1

The ArrayList can't have gaps. You can't add an element to the 15'th position if you haven't added elements to the 0 to 14 positions first.