Question

I have the following method:

  private <E extends Number> double GetAverage(ArrayList<E> al)
  {
    double total = 0;
    Iterator<E> itr = al.iterator();
    while(itr.hasNext())
    {
      total += itr.next();
    }

    return total;
  }

but it does not compile. I get a

“total cannot be resolved or is not a field”

on line

“total += itr.next();”

I understand that Java doesn’t know the value of E, but I hope you understand what I mean, what is the best way to create a generic method that adds the total(Numeric values) of an ArrayList.

Answer 1

There’s actually syntax errors with your code, you have line that’s not complete. Your full code should be:

private <E extends Number> double GetAverage(ArrayList<E> al) {
    double total = 0;
    Iterator<E> itr = al.iterator();
    while (itr.hasNext()) {
        E next = itr.next();
        total += next.doubleValue();
    }

    return total;
}

Note: the return of ‘total’ and not undefined retVal