List<?> is not equivalent to List<? extends Object>

Rémi Forax forax at
Mon Apr 21 06:54:01 PDT 2008

Hi all,
the JLS currently considers that List<? extends Object> is not 
equivalent to List<?>.
List<?> is reified but not List<? extends Object> so they behave 

It's not a big problem in general, if you want a List<?>, you declare a 
But (there is always a but), when the compiler infers a type argument
it's more problematic, by example,

HashSet<Class<?>> constantClassSet=new HashSet<Class<?>>();
  String.class, Object.class

emits a warning because the second line creates an array of
Class<? extends Object> which is not safe.

I think it's stupid, i propose to modify section (JLS3) to
add a line saying that if an inferred type argument is Type<? extends Bound>
with Bound the bound of the type varaible of Type, it is inferred Type<?>.


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