Examine Problems that Require the Mediator Pattern.
The Mediator Pattern in Software Development: Addressing Key Challenges
Question: What types of challenges arise in software development which require the Mediator Pattern?
In the domain of software engineering, as systems grow in complexity and components increase in number, the inter-relationships between these components can become convoluted. It is within this landscape that the Mediator pattern emerges as an indispensable tool in a designer’s arsenal. This pattern promotes a reduction in the number of interconnections between a set of system components by centralizing external communications.
When such a centralized controller known as the Mediator is introduced, components can operate without explicit knowledge of their counterparts.
Key Challenges Addressed by the Mediator Pattern:
Tight Coupling: As individual components (often referred to as colleagues in the context of the Mediator pattern) directly communicate with one another, their inter-dependencies proliferate, leading to a tightly coupled system. This can make the system brittle, difficult to modify, and hard to understand. The Mediator pattern decouples colleagues by ensuring they only communicate with the Mediator and not with each other directly.
Maintainability and Scalability: Direct communications between numerous components can make the system challenging to maintain or scale. When adding a new component or changing an existing one, a developer must understand and possibly modify many inter-component communication paths. The Mediator centralizes and simplifies these paths, making the system more maintainable and scalable.
Reuse and Isolation: In tightly interconnected systems, reusing a single component can be challenging since it may be heavily intertwined with other components. By employing the Mediator, components become more isolated and encapsulated, making them easier to reuse in different contexts.
Complex Business Logic: When there's intricate business logic that determines how components interact, it can be messy to distribute this logic across individual components. The Mediator pattern provides a centralized place where this complex logic can reside, promoting cleaner and more focused component design.
Overwhelming Component Responsibilities: Without a mediator, individual components might take on responsibilities beyond their primary function, such as managing communications with multiple other components. This can lead to violation of the Single Responsibility Principle. A Mediator offloads these communication responsibilities, ensuring components remain focused on their core functionality.
Consistency in Communication: When multiple components require a standardized way of interacting, having a Mediator ensures that there's a uniform protocol or set of rules for communication, eliminating disparities and potential inconsistencies.
To summarize, the Mediator pattern plays a pivotal role in addressing challenges related to system complexity, component inter-communication, and maintainability. By providing a centralized communication hub, it offers a structured approach to manage interactions, fostering cleaner, more modular, and scalable software architectures.
Out of all the design patterns, the Mediator pattern has probably been reinvented more times than any other. It is an absolutely essential pattern any time you have many different components of a system which have to maintain a consistent state as a whole. It is used by any system in which many different parts must work together efficiently while sharing the same basic information. We are going to use the Mediator pattern to manage the traffic lights in our traffic system.
1) Suppose the pedestrian wants to cross the street and pushes the button on the North light. The north light must now synchronize with the other lights
2) It has to tell the east and west lights to turn yellow, then red. It also has to wait until they respond that they have in fact done so.
3) It must also tell the south light to provide a walk signal. The south light must also respond.
4) Every change in any light requires all four lights to go through a complicated sequence of request and response
The Motivation behind the Mediator Pattern
In order to have good object oriented design, we have to create many classes that interact with each other.
If certain principles are not applied, the final framework will be incohesive, where each object relies on many other objects in order to perform their function. In order to avoid tightly coupled frameworks, we need a mechanism to facilitate the interaction between objects so that objects are not aware of the existence of other objects. Let us take the example of a user interface for an application. When we create the GUI, we add all sort of controls to the screen. One control needs to interact with all the other controls. For example when a button is pressed, it must know if the data is valid in other controls. If you created different applications using forms, you do not have to modify each control class each time you add a new control to the form. All the operations between controls are managed by the form class itself and this is known as the mediator pattern.
As you add more complicated intersections with turn signals, turning lanes, and more, the complexity grows.
You need a way of untangling all these connections. The Mediator pattern provides it.
In general, object-oriented applications consist of a set of objects that interact with each other for the purpose of providing a service.
This interaction can be direct (point-to-point) as long as the number of objects referring to each other directly is very low.
Figure 1 depicts this type of direct interaction where ObjectA and ObjectB refer to each other directly.
Figure 1: Point to Point Communication in the case of two objects
As the number of objects increases, this type of direct interaction can lead to a complex maze of references among objects (Figure 2), which affects the maintainability of the application. Also, having an object directly referring to other objects greatly reduces the scope for reusing these objects because of higher
coupling.
Figure 2: Point-to-Point Communication with an increased number of objects.
