[jboss-dev] Does this seem like a compiler bug?

[Scott M Stark]

I ran into a problem with the following code that compiles in eclipse,
but fails under the sun jdk:

   public void testClassCollection()
   {
      Collection<Class<?>> c = null;
      Collection<Class> ce = (Collection<Class>) c; // This is a warning
in eclipse, error under sun jdk.

This seems like an overly strict check. I can understand it for types
that allow mutable operations with respect to the wildcard parameter,
such as a Collection of List<?>:

   public void testCollectionOfUknownlistAdd()
   {
      Collection<List<?>> coul = new ArrayList<List<?>>();
      List<?> lw = coul.iterator().next();
      // This is an error because don't know what ? is
      lw.add(new Object());
      Collection<List> col = (Collection<List>) coul;
      List l = col.iterator().next();
      // This is allowed for legacy usage
      l.add(new Object());
   }

but I don't see how I can unsafely use Class in place of Class<?>. Its
equivalent to this safe read-only usage of an unknown collection, which
eclipse does allow, but the jdk does not:

   public void testCollectionOfUknownlistGet()
   {
      Collection<List<?>> coul = new ArrayList<List<?>>();
      List<?> lw = coul.iterator().next();
      // This is fine because ? although unknown, is still an Object
      Object o1 = lw.get(0);
      Collection<List> col = (Collection<List>) coul;
      List l = col.iterator().next();
      Object o2 = l.get(0);
   }