K & B Generics Self Test Q16

[palla sridhar]

When i try to compile the following code, i get a COMPILER ERROR.

  
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?
 
 

The answers given are:

   
1.
ArrayList<Integer> input = null; 
 
List<Integer> output = null; 
 
2.
List<Number> input = null; 
 
List<Number> output = null; 
 
3.
List<Integer> input = null; 
 
List<Integer> output = null;
 

Can anyone explain why these answers give a COMPILER ERROR still ??. My doubt is how can List<Integer> or List<Number> be assigned a List<? super Integer> or List<? super Number>.....

[ahmed yehia]

See K&B errata, the correct signature is:

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

[palla sridhar]

Thank you Ahmed, for showing the Error and also let me know abt the Errata..
Can you tell me the link where i can get proper ERRATA for K&B. In javaranch, its not so clear..