Get index of newly added item in a list?

Question

I want to get the index of a newly added element into an arraylist. e.g.

List listA = new ArrayList();

// Lots of code adding and removing things from `listA`, imagine `listA` now 
// contains approx 10,000 records

listA.add("element 0");

How do I find out the index of the newly added item?

I think that perhaps, I need a different data structure, but cannot think of what to use.

Answer 1

The first element added to the list would have index 0.
The last element added would have the index listA.size()-1.
However, you should note that if you remove elements from the list, some of the indices (indices of elements that had higher index than the removed element) would change. For example, if you remove the n'th element, the former (n+1)'th element would become the n'th element.

Thanks talex for the comment. I forgot about indexOf(), which returns the index of the supplied element (if that element is found in the list). However, this requires linear search time.

If you wish to treat the indices of the list as keys to find the values stored in the list, you might be better off using a HashMap<Integer,String>.