class DecoratedList<T> extends List<T>
{
    List<T> baseList;
    int size() {
        return baseList.size();
    }
    //..like the method above, but for every method on List..

    //The added behaviour
    T secondThing() {
        return baseList.get(1);
    }
}

class DecoratedList<T> extends ArrayList<T>
{
    //The added behaviour
    T secondThing() {
        return list.get(1);
    }
}

class DecoratedList<T> extends List<T>
{
    List<T> baseList;

    //pseudocode
    methodNotFound(method, arguments) {
        method.InvokeOn(baseList, arguments);
    }

    //The added behaviour
    T secondThing() {
        return baseList.get(1);
    }
}