List<Object> and List<?>

Why cant I do this:

List<Object> object = new List<Object>();

You can't do this because List is an interface, and interfaces cannot be instantiated. Only (concrete) classes can be. Examples of concrete classes implementing List include ArrayList, LinkedList etc.

Here is how one would create an instance of ArrayList:

List<Object> object = new ArrayList<Object>();

I have a method that returns a List<?>, how would I turn that into a List<Object>

Show us the relevant code and I'll update the answer.