# Purpose

The Mediator pattern aims to reduce the complexity of communications between multiple objects or classes by centralizing the interaction in a single place.

# Problem

• High Coupling: Too many direct connections between classes make the system fragile.

• Complex Communication: Difficult to understand and maintain the flow of messages between multiple components.

# Solution

• Centralization: Classes communicate only through a central mediator object.

• Simplification: Control logic of interaction resides in a single point, decoupling the colleagues.

# Structure

# Participants

• Mediator: Defines the communication interface.
• ConcreteMediator: Coordinates the actual communication between colleagues.
• Colleague: Base class/interface for components.
• ConcreteColleague: Objects communicating via the mediator.

# When to Use It

When there are many objects interacting in a complex but well defined way, and you want to centralize the communication logic.

# Example: Air Traffic Control

Management of control tower, airplanes and runways without direct communication between aircraft.

# Java Code

interface AirTrafficMediator {
    void register(Component c);
    void send(String msg, Component c);
}

class TowerMediator implements AirTrafficMediator {
    private List<Component> comps = new ArrayList<>();
    public void send(String msg, Component origin) {
        for (Component c : comps) if (c != origin) c.receive(msg);
    }
}

# Mapping Participants

• Tower (Mediator): Central coordination point.
• Airplane/Runway (Colleagues): Isolated components.
• AirportSystem: Client.

# Conclusions

Ideal for systems where multiple objects must collaborate without having a tangled network of dependencies.

# Related Patterns