Wildcards vs. generic methods

Posted by FredOverflow on Stack Overflow See other posts from Stack Overflow or by FredOverflow
Published on 2010-05-02T09:36:03Z Indexed on 2010/05/02 9:47 UTC
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Is there any practical difference between the following approaches to print all elements in a range?

public static void printA(Iterable<?> range)
{
    for (Object o : range)
    {
        System.out.println(o);
    }
}

public static <T> void printB(Iterable<T> range)
{
    for (T x : range)
    {
        System.out.println(x);
    }
}

Apparently, printB involves an additional checked cast to Object (see line 16), which seems rather stupid to me -- isn't everything an Object anyway?

public static void printA(java.lang.Iterable);
  Code:
   0:   aload_0
   1:   invokeinterface #18,  1; //InterfaceMethod java/lang/Iterable.iterator:()Ljava/util/Iterator;
   6:   astore_2
   7:   goto    24
   10:  aload_2
   11:  invokeinterface #24,  1; //InterfaceMethod java/util/Iterator.next:()Ljava/lang/Object;
   16:  astore_1
   17:  getstatic   #30; //Field java/lang/System.out:Ljava/io/PrintStream;
   20:  aload_1
   21:  invokevirtual   #36; //Method java/io/PrintStream.println:(Ljava/lang/Object;)V
   24:  aload_2
   25:  invokeinterface #42,  1; //InterfaceMethod java/util/Iterator.hasNext:()Z
   30:  ifne    10
   33:  return

public static void printB(java.lang.Iterable);
  Code:
   0:   aload_0
   1:   invokeinterface #18,  1; //InterfaceMethod java/lang/Iterable.iterator:()Ljava/util/Iterator;
   6:   astore_2
   7:   goto    27
   10:  aload_2
   11:  invokeinterface #24,  1; //InterfaceMethod java/util/Iterator.next:()Ljava/lang/Object;
   16:  checkcast   #3; //class java/lang/Object
   19:  astore_1
   20:  getstatic   #30; //Field java/lang/System.out:Ljava/io/PrintStream;
   23:  aload_1
   24:  invokevirtual   #36; //Method java/io/PrintStream.println:(Ljava/lang/Object;)V
   27:  aload_2
   28:  invokeinterface #42,  1; //InterfaceMethod java/util/Iterator.hasNext:()Z
   33:  ifne    10
   36:  return

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