Instantiating a Generic Class of Type <?>

I'm studying for the SCJP/OCPJP and I came across a sample question that seams strange to me.

The sample code instantiated two generic collections:

List<?> list = new ArrayList<?>();
List<? extends Object> list2 = new ArrayList<? extends Object>();

The "correct" answer to the question was that this code would compile but adding to either collection would produce a runtime error.

When I try to compile code like this I just get errors. The Java tutorial does not even show this type of code, it instead usually uses wildcards as a part of an upcast.

Collection<?> c = new ArrayList<String>();

Are the two generic collections above even legitimate code? The second by my logic would only disallow interfaces. The first one looks completely useless. Why use a generic that makes no attempt at control?

Check out the excellent Java generics tutorial PDF. More specifically the section about wildcards contains the answer to your question, and I quote

Collection<?> c = new ArrayList<String>();
c.add( new Object() );

Since we don’t know what the element type of c stands for, we cannot add objects to it. The add() method takes arguments of type E, the element type of the collection. When the actual type parameter is ?, it stands for some unknown type. Any parameter we pass to add would have to be a subtype of this unknown type. Since we don’t know what type that is, we cannot pass anything in. The sole exception is null, which is a member of every type.