Doubt about generic method

Question

i have a generic method has shown below
public static <E extends Number> <E>process(E list){
List<Interger> output = new ArrayList<Interger>(); or List<Number> output = new ArrayList<Number>();
return output ;
if delcare the output variable using Interger or Number . when i am returning the output . it is showing me compiler error and it suggests me to add cast List<E>. Why i not able understand. please clarify my doubt.
Thanks
Sura.Maruthi
Edited by: sura.maruthi on Sep 21, 2008 9:48 PM

Answer 1

Your method declaration is garbled; there can be only one <...> clause, eg
public static <E extends Number> E process(E list);This declaration says that for any subclass E of Number, the method process takes a single E instance (called list!?) and returns a single E instance. A valid implementation would be
return list;I'm guessing you want the parameter to have type List<E>?. Like this:
public static <E extends Number> E process(List<E> list);This declaration says that for any subclass E of Number, the method process takes a list of E's and returns a single E instance. A valid implementation would be
return list.get(0);Or perhaps you also want to return a list of numbers?
public static <E extends Number> List<E> process(List<E> list);This declaration says that for any subclass E of Number, the method process takes a list of E's and returns another list of E's. A valid implementation would be
return list;Note that you cannot just return a list of Integers or Floats, because your generic method must work for any subclass of Number, and you're promising to return back a list of the same type as the argument passed in.
Edited by: nygaard on Sep 22, 2008 10:05 AM