FULL PRODUCT VERSION :
C:\Program Files\Far>java -version
java version " 1.7.0_09 "
Java(TM) SE Runtime Environment (build 1.7.0_09-b05)
Java HotSpot(TM) Client VM (build 23.5-b02, mixed mode, sharing)

ADDITIONAL OS VERSION INFORMATION :
windows xp

A DESCRIPTION OF THE PROBLEM :
Javac forbids cast Class<Generic> be cast to Class <? extends Generic<?>>

In turn, is Class<Generic> probably distinct from Class<? extends Generic<?>> (given that their erasures are the same) ?

In turn, is 'Generic' probably distinct from '? extends Generic<?>>' ?

No, because |Generic| <: |Generic<?>|.

(JLS3 was not clear on this point. If both type arguments were ground types, JLS3 could prove them distinct and stop the cast, e.g. Class<String> can never be cast to Class<Integer> because Class<String> is distinct from Class<Integer> because String is distinct from Integer. However, JLS3 could not handle one or two wildcard type arguments. JLS7 takes the upper bound of a wildcard type argument - Generic<?> - and considers it against the ground type argument - Generic - to conclude that the type arguments are basically related.)

Therefore, there is no need for a compile-time error.

Since Class<Generic> is not a subtype of Class<? extends Generic<?>>, the cast is unchecked, and a compile-time unchecked warning is due.

Alex




STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
compile provided sample code

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
no errors
ACTUAL -
errors

ERROR MESSAGES/STACK TRACES THAT OCCUR :
javac:
Casting.java:4: error: inconvertible types
                  Class<? extends Generic<?>> generic = (Class<? extends
Generic<?>>) Generic.class;

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
class Generic<T> {}
public class Casting {
     void test() {
         Class<? extends Generic<?>> generic = (Class<? extends Generic<?>>) Generic.class;
      }
}


---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
compile code with Eclipse Juno