The interaction between objects by passing messages can be shown by interaction diagrams as well. A single interaction diagram describes the behavior of a special application case over time. The behavior is shown from an external point of view, which is characterized by the messages an object receives and the messages an objects sends to other objects or to itself.
At the top, there are the concerned objects. The dashed lines below represents the time flow. The interactions are arrows from and to the dashed lines, marked with the represented action, e.g. the message.
So one special case of the interaction of controller and counter may look like this:
