Hi
I suggest you to go thru the k&B 1.5 book, its explain this very nicely.
I can just give you some hints that
<T super Number> means T is a super class of Number, actually which is not correct, so it can not work.
The abstract class Number is the superclass of classes Byte, Double, Float, Integer, Long, and Short.
<T extends Number> means Number is a super class and T is extending that class, so it is valid and we can pass T as Interger, Long etc.