Maintaining Consistent Abstractions

A class mixes responsibilities when it combines domain logic with unrelated concerns like serialization, persistence, or formatting. For example, an Employee class with both calculateAnnualSalary() and toJSON() methods violates single responsibility. Each concern should live in its own focused class to maintain cohesion and separation of concerns.

Extract serialization into dedicated serializer classes rather than adding toJSON() or toString() methods to your domain class. This keeps domain logic pure and lets you serialize the same object in multiple formats without bloating the original class. Repositories handle persistence the same way.

Refactor during class design, code reviews, or when extending existing classes. Watch for classes where domain methods like calculate() sit alongside persistence methods like save() or serialization methods like toJSON(). These mixed concerns are prime refactoring targets to improve maintainability.

Mixed concerns make classes harder to understand, test, and modify. Changes to how you store data shouldn't require touching business logic. Separation of concerns ensures each class has one reason to change, reducing bugs and making the codebase easier to extend.

Yes. Analyze existing classes for mixed concerns during refactoring or code review cycles. Identify where domain logic, serialization, and persistence overlap, then extract each concern into its own class or dedicated component. This improves temporal cohesion gradually.

Clean API design depends on single-purpose abstractions. When each class represents one cohesive idea, your API contracts become clear and stable. Mixed abstractions create confusing interfaces that force consumers to understand multiple unrelated concerns.