java generic addition

Question

I\'m attempting implement the add method mentioned in the Generic sparse matrix addition question

class Matrix
{
  private T add(T left,          


        

Answer 1

"I'm not sure what I'm missing since T extends Number and Integer is a subclass of Number."

This statement is false. In general if you have:

 public class B extends A {
 }

 public class C extends A {
 }

it does not mean that B can be cast to C. So writing something like:

 public  T method(T arg) {
     return (B)arg;
 }

and you calling it with B b = (B)method(C); is obviously wrong.