How to modify numbers in a arraylist?

Question

Say I have an arraylist with these values:
[item1, 65, 555.5]item1 represents the name of an item type, 65 represents the number in stock, and 555.5 represents the value of one item.
Now say I want to add 10 item1's to the number in stock. So I want to change the 65 in the array list to a 75. How could I do this?
Thanks

Answer 1

This would be a lot easier if you created a class to encapsulate those three data members, then created a list of those objects. The class could have three variables, name, stock, and value. Then it's easy to write a method to add or subract to the stock of a particular item, and you don't have to worry about modifying the wrong element in the list, casting elements to the right type (String, int, float, etc).
public class Item {
    private String name;
    private int stock;
    private float value;
}