What is a code smell?

Code smells are not errors but signals of deeper problems in the codebase. They typically stem from suboptimal practices like poor naming conventions, excessive complexity, or lack of cohesion that are visible, for example, large classes or long methods. Recognizing and addressing code smells early helps improve code quality, maintainability, and the ease of future updates.

Specific examples of code smells differ depending on the programming language, developer, and methodology; however, common examples include:

• Duplicate code: The same logic is repeated in multiple places, which leads to higher maintenance costs.
• Long methods: Overly lengthy functions become harder to understand and debug.
• God classes: Take on too many responsibilities, violate the single responsibility principle, and hinder modularity.
• Feature envy: When a method in one class excessively relies on data or behavior from another, suggesting poor data encapsulation.
• Switch statements: If they violate the open-closed principle.
• Comment-heavy code: Indicate unclear logic that needs explaining rather than self-documenting code.

Identifying code smells involves observing patterns like overly complex methods, excessive dependency on external classes, or violation of the design principles of a specific development language. There are three ways to identify code smells:

• Manual inspection: Peer reviews with clear guidelines on code help detect obvious code smells.
• Automated tools: SonarQube, JDeodorant, and PMD are examples of instruments that identify code smells.
• Code metrics: Analytics can indicate if code is too complex or methods are too long.

Maintaining regular reviews and inspections is effective in detecting smells by highlighting areas of inefficiency or potential design flaws.

To avoid code smells, developers must follow best practices according to the code language and methodology they are using, as well as the expectations of their team. The SOLID principles provide a framework for doing this:

Each class or module should have a single reason to change, with only a single responsibility to ensure focus and easier maintenance.

Software entities like classes, modules, and functions should be open for extension but closed for modification. New functionality should be added by extending the existing code, not altering it.

Objects of a superclass should be replaceable with objects of a subclass without affecting the correctness of the program.

A class should not be forced to implement interfaces it does not use. Instead, create smaller, more specific interfaces to prevent unnecessary dependencies.

High-level modules should not depend on low-level modules; both should depend on abstractions. Abstractions should not depend on details; details should depend on abstractions, promoting decoupled and flexible design.

By adhering to these principles, refactoring regularly, and conducting peer and individual code reviews, developers can avoid creating code smells and produce higher-quality code.