Wildcards vs. generic methods
- by FredOverflow
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
