The Mediator design pattern provides a solution:
Define a separate Mediator object that encapsulates how a set of objects interact.
Objects interact with a Mediator object
instead of interacting with each other directly.
Describing the Mediator design in more detail is the theme of the following sections.
See Applicability section for all problems Mediator can solve.

• The key idea in this pattern is to let objects interact with each other indirectly through a common Mediator object that controls and coordinates the interaction.
• Define a separate Mediator object:
  • Define an interface for interacting with colleagues (Mediator | mediate()).
  • Define classes (Mediator1,…) that implement the interaction behavior by controlling and coordinating the interaction between colleagues.
• This enables compile-time flexibility (via class inheritance).
  New colleagues can be added and the interaction behavior of existing ones can be changed independently by defining new Mediator (sub)classes.
• Colleagues delegate interaction to a Mediator object (mediator.mediate()).
• This makes colleagues loosely coupled because they only refer to and know about their mediator and have no explicit knowledge of each other.
  "[…] each colleague communicates with its mediator whenever it would have otherwise communicated with another colleague." GoF [p277]