Question

I use Java. when I use ArrayList in Java. if I access index number randomly.

Is this posible?

If this is not posible. How should I do?

For example

ArrayList<String> al = new ArrayList<String>();
al.add(100,"stackoverflow");

Is this posible?

Answer 1

What you seem to need isn’t an arrayList but a map between integers and strings :

HashMap<Integer,String> mymap = new HashMap<Integer,String>();

So you can write

mymap.put(100,"stackoverflow");

And

String myString = mymap.get(100);

Adding onto why you cannot use an arraylist:

When you first initialize an ArrayList, the size is zero. Attempting to add at an index that is larger than the size will still throw an IndexOutOfBounds exception just like an array would. The benefit of the ArrayList is that it will dynamically allocate more memory should the size fill up.

Besides, arrays aren’t efficient for “sparse arrays” even if you make the effort to manage the size to avoid errors.