Generics.....problem

[Debajit Paul]

List <? super Integer> al = new ArrayList<Number>(); //line 1
al.add(12); //line 2
al.add(12+ 13); //line 3
for (Number no:al) //line 4
{
System.out.println(no);
}
14)What will be the possible result of the above program?
a) Error at Line 1
b) Error at Line 2
c) Error at Line 3
d) Error at Line 4
e) Compile and execute Sucuessfully


ANS:
d)Error.Because in the declaration we have specified any super type of Integer,But in for
each loop we are specifying Number,We cannot restrict whenever we are using
lowerbound.So accepatble thing in line 4 is for (Object no:al).

Can any1 give clarification on this......?

[Raghavan Chockalingam]

i think the answer is correct as the line1 itself is invalid. you cannot assign an object of base class to its child class.

casting: allowed only subclass to parent class, i.e. up the hierarchy

[Ben Souther]

Debajit Paul,
Please QuoteYourSources when posting mock questions. If a valid source is not added to this question soon, it will need to be removed.

[Ivan Ivanic]

Originally posted by Raghavan Chockalingam:
i think the answer is correct as the line1 itself is invalid. you cannot assign an object of base class to its child class.

casting: allowed only subclass to parent class, i.e. up the hierarchy

yes generally. but in this case of generics it will accept only classes that are superclass of Integer i.e. Number
if it was declared as <? extends Integer> than you answer would be valid.