Question

How does this Java statement compile without warnings?

Class<Integer> x = int.class;

even though

Integer.class != int.class

Edit: Putting it a different way, it seems as though Integer.class and int.class have nothing in common (see comments below), so why does it make sense for this assignment to be possible?

Answer 1

After a whole lot of searching, I came across this little snippet in the JLS, section 15.8.2 Class Literals:

If p is the name of a primitive type, let B be the type of an expression of type p after boxing conversion (§5.1.7). Then the type of p.class is Class<B>.

The spec doesn’t explain why this is so, instead of Class<?> for example. I have also been unable to find any evidence that this is related to either generics or autoboxing.

Integer is a first-class object whereas int is a primitive type, and most methods of Class such as isInstance, isAssignableFrom and cast which operate on Objects are invalid in the context of int.class. Consequently, I do not see any reason why the type of int.class is Class<Integer>.