How does one handle a java method which returns a non-public sub-type via reflection?

[jeffrey kutcher]

 The idea is not to be specific, but to be general. This is an example. In practice, I don't know what "o" is and so there has to be a discovery phase. I'm not sure how to make it more general than discovering the class via o.getClass(). As in this example, yes the class object returned is an ObservableList but I'm unable to add an object to this list via reflection. Why? And what can be done to change that? Why should it be changed? Because an object can be added to the list via vbox.getChildren().add(). Therefore an object should be permitted to be added via introspection. The avenue for the addition is different, the end result should be the same.
There are lots of other classes in the Java libraries that have this same issue. 
There's also the issue of what gets returned can be many different types. How do you figure out which type should be returned? Not a trivial question; not so sure there's an answer. In this case, all I need is a List. Not an ArrayList, or an ObservableList, LinkedList, SortedList .... Please don't focus on this ... yet. Original issue first.
    On Friday, January 12, 2018, 1:25:13 PM CST, mandy chung <mandy.chung at oracle.com> wrote:  
 
  
 
 On 1/12/18 10:26 AM, jeffrey kutcher wrote:
  
             m = o.getClass().getMethod("add", new Class[] { Object.class, });
            o = m.invoke(o, new Object[] { button1, }); 
 
 o.getClass().getMethod(...) is an anti-pattern for finding a public method.   Object.getClass() returns the implementation class while you want to invoke a public method `javafx.collections.ObservableList::add` in this case.  In this case, the declaring class of the method is known and so one way to fix it is to use the specific Class:
 Class<?> observableListClass = javafx.collections.ObservableList.class;
m = observableListClass.getMethod("add", new Class[] { Object.class, });
o = m.invoke(o, new Object[] { button1, });

Mandy