Confusion: IllegalAccessException with reflection

Question

Hi,
Lets say that I have an opaque object that I know implements
the java.util.Set interface.
Its concrete type is in fact (from exception trace)
java.util.AbstractMap$1
Now I want to get the Method for "iterator" for this object.
I have access to both the concrete java.lang.Class (obviously)
and thru extra work the java.lang.Class for Set.
Intuitively, I would think that doing a Class.getMethod() with the
Set Class would not be best because this would not guarantee
that I am actually invoking the most concrete derivation of "iterator".
In fact, the interface Set has no implementation for "iterator".
But when I use the Class for java.util.AbstractMap$1 for the Class.getMethod("iterator")
call, I do get a result, but that method is not invocable due
to IllegalAccessException. When I do a
java.lang.Set.class.getMethod("iterator", null) and then use the Method.invoke()
for an object of type java.util.AbstractMap$1, this seems to work.
Can anyone explain why NOT to use the concrete Class type for
the getMethod() call? This implies that java.lang.Method for abstract classes
successfully invokes different actual subroutines for different actual objects of
different derivation levels.
Andy

Answer 1

>
Intuitively, I would think that doing a
Class.getMethod() with the
Set Class would not be best because this would not guarantee
that I am actually invoking the most concrete
derivation of "iterator".
In fact, the interface Set has no implementation for
"iterator".
If I am reading that correctly then your intution is wrong.
For an instance there is only one possible method call. There is no way to call a different method with that instance regardless of what you do to it.
A cast never changes the type of an object, all it does is verify that that an instance is of that type.