How can I annotate in a UML class diagram that an instance of ClassA is registered as an observer of an instance of ClassB? (Both implement the appropriate interfaces).
This doesn't really belong in a class diagram, because they are static, but if this is something that is important to the design - how can you annotate it in this type of diagram?
To clarify: I know how to annotate the Observer pattern in UML. My question is more specific.
ClassA being registered as an observer to ClassB is important for the design, however I'm not sure if an association relationship between the two classes is appropriate, since ClassA and ClassB don't know about each other. They're totally decoupled, and only connected through the Observer pattern.