Extending a java ArrayList

Question

I\'d like to extend ArrayList to add a few methods for a specific class whose instances would be held by the extended ArrayList. A simplified illustrative code sample is be

Answer 1

Here is my suggestion:

interface ThingStorage extends List {
    public int total();
}

class ThingContainer implements ThingStorage {

    private List things = new ArrayList();

    public boolean add(Thing e) {
        return things.add(e);
    }

    ... remove/size/... etc     

    public int total() {
        int tot = 0;
        for(int i=0; i < size(); i++) {
            tot += ((Thing)get(i)).getAmt();
        }
        return tot;
    }

}

And report() is not needed actually. toString() can do the rest.