Single Responsibility Principle: Why Each Class Should Do Only One Thing

The Single Responsibility Principle (SRP) states that a class should have only one reason to change, meaning it should handle just one distinct responsibility. Classes that bundle multiple concerns — such as validation, database access, notifications, and logging — are known as God Classes and are considered an anti-pattern in software design. A useful analogy compares a Swiss Army knife, which breaks as a whole unit when one tool fails, to a scalpel, which is purpose-built and replaced only when it specifically malfunctions. In practice, SRP underpins popular architectural patterns like MVC, Hexagonal, and Clean Architecture, where each layer owns a clearly defined role. Refactoring a bloated class into focused units — such as separate classes for validation, persistence, and email — makes codebases easier to maintain, test, and scale.