How to move specific item in array list to the first item

Question

For example : A list

A B C D E

Given C , Switch to

C A B D E

Notice that the array size will change, some items may removed in run times

Collections.swap(url, url.indexOf(itemToMove), 0);

This statement is not working because it output C B A D E not C A B D E , how to fix it?

Thanks.

Answer 1

What you want is a very expensive operation in an ArrayList. It requires shifting every element between the beginning of the list and the location of C down by one.

However, if you really want to do it:

int index = url.indexOf(itemToMove);
url.remove(index);
url.add(0, itemToMove);

If this is a frequent operation for you, and random access is rather less frequent, you might consider switching to another List implementation such as LinkedList. You should also consider whether a list is the right data structure at all if you're so concerned about the order of elements.