Question

Found an interesting thing about ArrayList,

ArrayList<String> list = new ArrayList<String>();
list.add(0, "0-element");
list.add(1, "1-element");
list.add(2, "2-element");

But if the elements are not coming in an unknown order, eg.

ArrayList<String> list = new ArrayList<String>();
list.add(1, "1-element");  // IndexOutOfBoundsException
list.add(2, "2-element");
list.add(0, "0-element");

You get IndexOutOfBoundsException, Is the only option here is to use a Map instead of List?

Answer 1

This is documented :

IndexOutOfBoundsException – if the index is out of range (index < 0 ||
index > size())

You could test before adding :

if (pos>=list.size()) list.add(element);
else list.add(pos, element);  

But what you do is strange (and that’s the reason why there is no method doing the test and adding/insertion). Do you really want to add at index (i.e. moving some of the previously inserted elements) ? Are you sure a standard array, allowing you to set elements at arbitrary index isn’t what you need ?