Chapter 10 of “Clean Code” shifts our focus from individual functions to the larger structures that contain them: classes. The book argues that well-designed classes are crucial for creating scalable and maintainable software. This chapter explores the principles of good class organization, emphasizing size, responsibility, and how to structure them to handle change effectively.

Chapter 10 – Classes

• Class Organization: The book starts by highlighting the importance of having a clear and logical organization within a class. Public constants should come first, then static variables, then private static variables, and so on. There’s a suggested order for members to make the class easier to read.
  • Encapsulation: A key aspect of class organization is encapsulation – keeping the data private and controlling access to it through well-defined methods. This prevents external code from directly manipulating the internal state of an object, making the code more robust and easier to change.
• Classes Should Be Small!: Just like functions, the book emphasizes that classes should be small. The smaller a class, the easier it is to understand what it does and how it works. When classes try to do too much, they become complex and hard to maintain.
  • The Single Responsibility Principle (SRP): This is a core principle of object-oriented design, and the book stresses its importance. A class should have only one reason to change. In other words, it should have only one responsibility. If a class has multiple responsibilities, changes to one responsibility might affect others, making the class brittle.
  • Cohesion: Cohesion refers to how closely the methods and variables within a class are related to each other. High cohesion means that the members of a class are working together towards a single, well-defined purpose. Small classes that adhere to the SRP tend to have high cohesion, making them more understandable and maintainable.
  • Maintaining Cohesion Results in Many Small Classes: The natural consequence of striving for high cohesion and adhering to the SRP is that you’ll end up with a larger number of smaller classes. While this might seem like more to manage initially, it actually leads to a more flexible and robust system in the long run because each class is focused and easier to change independently.
• Organizing for Change: Software is constantly evolving, and our classes need to be designed in a way that minimizes the impact of changes. The book discusses strategies for organizing classes to make them more resilient to modifications.
  • Isolating from Change: One key technique is to design classes so that they depend on abstractions (like interfaces) rather than concrete implementations. This principle, often related to the Dependency Inversion Principle (DIP), helps to isolate classes from the details of other classes that might change. By depending on stable abstractions, your classes are less likely to be affected when concrete implementations are modified.

Clean classes aren’t just about tidy code, they’re about design that stands the test of time. Chapter 10 shows how principles like SRP, cohesion, and encapsulation guide us toward systems that are easier to understand, modify, and extend. A clean class should feel like a well-composed sentence: clear in purpose, structured logically, and impossible to misinterpret. As your systems grow, small, focused classes will be your greatest ally.