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doubt abt Generics mock question - from K&B

 
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Given a method declared as:



A programmer wants to use this method like this:

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.

the answers are B, E and F.

as if B is "ArrayList<Integer> input = null",
WHY would process(input) works, as the method's parameter declared as process(List<E> nums), type of List not ArrayList?
 
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Because



Bu.
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