Question about capture conversion

Question

Hi, relating to capture conversion and to the code below:
public static void reverse(List<?> list) {
          rev(list);
     private static <X> void rev(List<X> l) {
     }Am I right in saying that the <X> (or whatever else for that matter), it's just giving a name to whatever type will be passed by the reverse method? The syntax looks strange since we are declaring a type in a void method, and since I'm an old fashioned Java 1.4 programmer I find a bit difficult to accept this new syntax; additionally
the JLS is not terribly simple in defining capture conversion :)
Message was edited by:
mtedone

Answer 1

First, is there any particular reason why you used:
Integer a = Integer.valueOf(1);while I used
Integer a = 1; //boxing
Just to get rid of boxing conversion as a possible issue--which it shouldn't be, but might as well keep it simple.
Integer a = Integer.valueOf(1);
Comparable<String> cs1 = a; // errorbecause we are assigning to a Comparable<String> an
Integer value, and that's illegal, since String and
Integer are not in a subtype relation (?)Something like that, yes. I'm not sure of the exact clause of the JLS that forbids it.
>
Comparable<Integer> ci = a; // ok
Comparable<String> cs2 = ci; // errorbecause we are assigning to a Comparable<String> a
Comparable<Integer>, and again, String and Integer
are not in a subtype relation (?)Yep.
Comparable<String> cs3 = c1; // warning
Comparable<String> cs4 = c2; // warningit's what I believe is called 'heap pollution' I forget what that term means, and am too lazy to look it up, so I'll take your word for it.
and I
believe that on first use a ClassCastException will
be thrown Sounds right. Run it and see for yourself.
(although the compiler behaves correctly by
flagging an unchecked warning, for compatibility with
legacy systems, etc)Right.