Types of Code Smells

About

Code smells can be categorized based on the kind of problem they indicate whether it's structural, behavioral, or related to object-oriented misuse. Understanding these categories helps in identifying and addressing them systematically.

Here are the most common types of code smells -

1. Bloaters

These are code elements that have grown too large or too complex, making them hard to understand and maintain.

• Long Method: A method that does too much or spans too many lines.

• Large Class: A class that tries to handle too many responsibilities.

• Long Parameter List: Methods with too many parameters, reducing clarity.

• Primitive Obsession: Overuse of primitive types instead of small domain-specific objects.

• Data Clumps: Groupings of variables that often appear together but are not encapsulated.

Refactoring: Extract method, introduce parameter object, replace primitives with objects.

2. Object-Oriented Abusers

These smells arise from violations of object-oriented principles such as encapsulation or inheritance.

• Switch Statements: Overuse of conditional logic instead of polymorphism.

• Temporary Field: Fields that are only sometimes used by an object.

• Refused Bequest: Subclass uses only some of the inherited methods or fields.

• Alternative Classes with Different Interfaces: Two classes that do similar things but have different method names.

Refactoring: Replace conditionals with polymorphism, extract subclasses, apply interface standardization.

3. Change Preventers

These smells make code hard to change or extend due to tight coupling or scattering.

• Divergent Change: One class needs to change for many different reasons.

• Shotgun Surgery: A single change requires edits in many different classes.

• Parallel Inheritance Hierarchies: Whenever you create a subclass in one hierarchy, you must create a corresponding subclass in another.

Refactoring: Move methods, collapse hierarchies, use delegation.

4. Dispensables

These are unnecessary or redundant code elements that clutter the codebase.

• Duplicate Code: Same logic appearing in multiple places.

• Dead Code: Code that is never executed or used.

• Speculative Generality: Code written for anticipated future use that never materializes.

• Lazy Class: Classes that are not doing enough to justify their existence.

• Comments: Overuse of comments in place of readable, self-explanatory code.

Refactoring: Remove, inline, or simplify code; rename methods for clarity.

5. Couplers

These smells indicate excessive dependencies between classes, violating the principle of low coupling.

• Feature Envy: A method that uses more features of another class than its own.

• Inappropriate Intimacy: Classes that are too familiar with each other's internals.

• Message Chains: A client asks one object for another and so on — a chain of method calls.

• Middle Man: A class that delegates most of its functionality elsewhere.

Refactoring: Move methods, hide delegate chains, use wrappers or facades.

6. Concurrency Smells

These arise when multi-threaded code is poorly structured:

• Shared Mutable State: Multiple threads accessing/modifying the same data unsafely.

• Excessive Locking: Unnecessary or broad synchronization that harms performance.

• Deadlocks: Circular dependencies in locks leading to blocked threads.

Refactoring: Use immutability, fine-grained locking, thread-safe constructs.

7. Architecture Smells

These occur at a higher level than individual classes or methods.

• Cyclic Dependencies: Modules or packages depend on each other circularly.

• God Object / God Class: A class that knows too much or does too much.

• Unstable Dependencies: High-level modules depend on low-level ones that change frequently.

Refactoring: Break cycles, extract services, enforce architectural boundaries.