How do you design interfaces between objects?

Interfaces in Object Oriented Design (OOD) play a pivotal role by promoting abstraction, modularity, and polymorphism. They allow for the separation of what an object does from how it achieves it, enabling different objects to interact seamlessly within the same context. My experience underscores the significance of carefully designing interfaces to foster system scalability and maintainability. By abstracting implementation details, interfaces ensure that components can evolve independently without affecting others. This principle aligns with the agile methodology, particularly Scrum, where adaptability and iterative development are key.

Interfaces enable loose coupling between components, making it easier to modify and extend software systems. By depending on interfaces rather than concrete implementations, components can be easily replaced or extended without impacting other parts of the system, promoting maintainability and scalability.

Designing interface is generally easier if the purpose of an interface is clear. In other words, if Single Responsibility Principle is followed which states that every class, method , interface must have a clear defined role. With this specific purpose in mind, we can clearly identify the relevant attributes and methods. However we must make sure that the method signatures (return type, type of exceptions it throws , parameters it takes) remain consistent across implementations. This consistency allows callers to interact with any implementation of the interface without worrying about which concrete class is being used.

Start with a brief summary of the interface, describing its purpose, role, and intended usage. Clearly state the high-level goals and responsibilities of the interface to provide context for developers. Document each method and property defined in the interface, describing its purpose, parameters, return values, and any exceptions it may throw. Use clear and concise language to explain what each member does and how it should be used. Provide examples or code snippets demonstrating how to use each method or property in different scenarios.

Look for signs of design issues, such as: 1. Large interfaces with too many methods or properties. Interfaces that violate the Single Responsibility Principle (SRP) by having multiple reasons to change. 2.Interfaces that are tightly coupled to specific implementations or technologies. 3.Look for common functionality shared among interface methods and properties.Extract that common functionality 4.Rename methods, properties, and parameters to better reflect their purpose and usage. 5.Ensure that interfaces are open for extension but closed for modification (Open/Closed Principle). 6.Break down large interfaces into smaller, more focused interfaces (Interface Segregation Principle).

Use TDD principles to drive the development of classes implementing the interface. Write failing tests based on the interface contract, implement the class to pass the tests, and refactor as needed. TDD ensures that classes adhere to the interface contract from the outset and promotes better design and testability.

You need to keep in mind the Interface Segregation Principle (ISP) which is one of the five SOLID principles of object-oriented design. It states that a client should not be forced to depend on interfaces it does not use. In other words, ISP emphasizes that interfaces should be fine-grained and specific to the needs of the clients that use them, rather than being large and monolithic. Instead of creating large interfaces that cater to multiple clients with different needs, ISP suggests breaking interfaces into smaller, more specialized interfaces that are tailored to specific clients or groups of clients. Each interface should represent a cohesive set of behaviours or capabilities that are relevant to a particular client or use case.