Avoiding the pitfalls of large, monolithic interfaces

In software development, the principle of "solid" stands for five important design principles that help create clean, flexible, and maintainable code. One of these principles is the Single Responsibility Principle (SRP), which states that a class or module should have only one reason to change. Applying this principle is crucial to avoid the pitfalls of large, monolithic interfaces.

Understanding the problem

When designing interfaces, it's tempting to include all the methods and properties that seem related to the purpose of the class. However, over time, as requirements change and new features are added, these interfaces tend to grow larger and more complex. This creates a monolithic interface that violates the SRP.

A monolithic interface becomes harder to understand, maintain, and test. It tightly couples different responsibilities within a single class or module, making it difficult to modify or extend individual components without affecting the others. Furthermore, it increases the risk of introducing bugs and hinders code reuse and modularity.

The benefits of small, focused interfaces

To avoid the pitfalls of large, monolithic interfaces, it is crucial to create small, focused interfaces that adhere to the SRP. By dividing the responsibilities into separate interfaces, we achieve several important benefits:

  1. Simplicity: Smaller interfaces are easier to understand and navigate. Developers can quickly grasp their purpose and functionality without having to dig into excessive code and unrelated methods.

  2. Modifiability: Focusing on single responsibilities allows for changes to be made more easily. Modifying one aspect of the system becomes less risky and does not ripple across unrelated components.

  3. Testability: Small interfaces make it easier to write unit tests, as we can isolate and test individual responsibilities. This enhances the overall code quality and stability.

  4. Reusability: When responsibilities are divided into separate interfaces, it becomes easier to reuse certain components in different contexts. Coupling is reduced, and developers can select the specific interfaces they need, promoting code modularity.

Applying the interface segregation principle (ISP)

To achieve small, focused interfaces, we can follow the Interface Segregation Principle (ISP), another cornerstone of the SOLID principles. The ISP states that clients should not be forced to depend on interfaces they do not use. By adhering to the ISP, we create interfaces that are specific to the needs of the clients, avoiding unnecessary dependencies.

To apply the ISP, start by analyzing the existing large interface and identify groups of methods that have a common purpose or usage. Create separate interfaces for each group, ensuring each interface serves a distinct and cohesive responsibility. Clients can then implement only the interface(s) they need.


Avoiding the pitfalls of large, monolithic interfaces is crucial for creating clean, modular, and maintainable code. By following the SOLID principle of Single Responsibility and applying the Interface Segregation Principle, we can divide responsibilities into small, focused interfaces. This leads to simpler, more modifiable, and testable code, promoting reusability and enhancing the overall software quality.

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