It seems as if this example implementation of the Observer pattern is drawn from the book Headfirst Design Patterns, OReilly, which I am currently reading. Here is a UML diagram from the book
It's not very cleanly visible, but the methods, composing the Subject Interface are:
What I am skeptical about is the last method. Why would the clients of the interface know about the specific way in which they are called? IMHO the place of this method is inside the concrete subject implementation -ConcreteSubject.