I'm not sure about the question 9: Which pattern allows an object to be notified whenever changes occur to some other object? I think it's the observer but the decorator is trowing me off. Is it the observer or decorator and why?
This just my opinion, I think that is observer because in the definition of observer pattern, when an object change, it will get notifications.
I also agree with Duc.
The decorator design pattern is a structural pattern and changes the object itself.
Observer, on the other hand, is a behavioral pattern and implements event handling (ex: adding an event/action after something is completed).
