Mediator vs. Observer Pattern

Mediator and Observer both reduce direct coupling, but they do it differently.

Mediator

Mediator says:

• one explicit coordinator should own the interaction rules
• participants report to the mediator
• the mediator decides what happens next

Observer

Observer says:

• a subject emits changes
• interested listeners react
• the subject does not coordinate all downstream behavior directly

Java Shortcut

Ask:

• “Do I need one place to coordinate many components?” -> Mediator
• “Do I need many listeners to react to a change?” -> Observer

The difference is central coordination versus distributed reaction.