Use Mediator in Java to reduce peer-to-peer awareness without hiding the collaboration rules that still need to be designed explicitly.
Mediator reduces tight coupling by replacing many peer-to-peer references with one coordination dependency. That can make the collaboration graph far easier to understand.
Without a mediator:
With a mediator:
That does not remove complexity. It relocates it into one explicit place.
Mediator is a win when the interaction rules become clearer after centralization. If they become harder to test or reason about, the design may be too centralized.