Question

I have an ArrayList as an Object(from reflection) and made my own class that extends off of it(ArrayListMonitor) that calls a function every time an arraylist has an item removed/added. But then I get this: java.util.ArrayList cannot be cast to ArrayListMonitor
I need to monitor the arraylist as I am loading a jar and creating a server from it, that has a clients field I need to monitor.

Answer 1

If the ArrayList is not of instance ArrayListMonitor this cannot work:

ArrayList<String> a = new ArrayList<String>();
ArrayListMonitor<String> am = (ArrayListMonitor<String>) a; // must throw ClassCastException

If you want to monitor the array list you have several options:

1. write a delegate like new ArrayListMonitor(a); and create delegates for all relevant methods in the ArrayList
2. Use a dynamic proxy to monitor ArrayList’s behaviour
3. use other techniques like AOP