Doubt in Generics

[Lata Bagga]

Hello Friends,

I have doubt in the following question which is Q no. 16(Chapter 7) from KS & BB of Generics and Collection:

Given a method declared as:
public static <E extends Number> List<? super E> process(List<E> nums)
 
A programmer wants to use this method like this:
// INSERT DECLARATIONS HERE
output = process(input);
 
Which pairs of declarations could be placed at // INSERT DECLARATIONS HERE to allow
the code to compile? (Choose all that apply.)
A. ArrayList<Integer> input = null;
ArrayList<Integer> output = null;
B. ArrayList<Integer> input = null;
List<Integer> output = null;
C. ArrayList<Integer> input = null;
List<Number> output = null;
D. List<Number> input = null;
ArrayList<Integer> output = null;
E. List<Number> input = null;
List<Number> output = null;
F. List<Integer> input = null;
List<Integer> output = null;
G. None of the above.    
 
Answer: B,E and F.
 

I am not able to understand why option C is not correct. As the return type is List<? super E> and if E is an Integer then List<Number> should work for it.
Can anyone help me with it?

Regards,
Lata

[Vitor Isaia]

Both sides (reference and object) need to be of the exaclty same generic type... even if one of the types extends the other one...

So "C" is wrong because the type is different... Number and Integer.
You can't have something like this:
List<Number> l = new ArrayList<Integer>();

Regards,

Vitor

[ahmed yehia]

This is an errata question, the correct method signature is:

public static <E extends Number> List<E> process(List<E> nums)