InterfaceSegregation

Interface Segregation Principle (ISP) is a design principle in object-oriented programming and one of the SOLID principles. It states that no client should be forced to depend on methods it does not use. To achieve this, interfaces should be small and specific rather than large and general-purpose.

Rationale and benefits: By splitting broad interfaces into smaller, cohesive ones, implementations only commit to the capabilities they actually need. This reduces coupling, minimizes the impact of changes, and makes code easier to understand, test, and evolve. Clients can depend on the exact interfaces that reflect their requirements.

Examples: A common example is a Worker interface with methods work() and eat(). If a class only needs to perform work, requiring it to implement eat() introduces unnecessary coupling. Splitting into Workable and Eater interfaces allows classes to implement only the relevant methods. Another example is a multifunction device with print(), scan(), and fax(). Instead of one interface listing all capabilities, define Printable, Scannable, and Faxable; devices implement only the features they support.

Implementation guidance: Analyze responsibilities and break large interfaces into smaller, task-specific ones. Prefer composition over a single fat interface. When designing public APIs, provide minimal, composable interfaces so that implementing classes and clients depend on what they actually need.

Impact: ISP promotes modular, maintainable, and testable code by reducing forced dependencies and enabling flexible reuse of interfaces across different components. It is most effective when used early in design and applied alongside other SOLID principles.