“Code smells” are subtle indicators of underlying problems in your codebase. They don’t crash your app or throw errors but can lead to long-term maintainability issues if left unaddressed. Let’s dive into what code smells are, examples of common smells, and how to clean them up.

What Are Code Smells?

• Coined by Martin Fowler in Refactoring: Improving the Design of Existing Code, code smells are symptoms of poor design or coding practices.
• They signal that something might need refactoring, even if it technically works.

🧠 Think of them as warning signs, not bugs. A bug means something is broken; a smell means your design could use improvement.

Common Code Smells and How to Fix Them

Long Methods

• The Smell: A single method tries to do too much (e.g., 200+ lines of code).
• Why It’s Bad: Hard to read, test, and debug.
• Fix: Break the method into smaller, single-purpose methods. Use meaningful names to make their purpose clear.

Before:

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public void processOrder(Order order) {     
	// Code for validating order     
	// Code for applying discounts     
	// Code for calculating total     
	// Code for sending confirmation email }

After:

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public void processOrder(Order order) {     
	validateOrder(order);     
	applyDiscounts(order);     
	calculateTotal(order);     
	sendConfirmation(order); 
}

Large Classes (God Objects)

• The Smell: A class tries to handle too many responsibilities.
• Why It’s Bad: Violates the Single Responsibility Principle (SRP). Hard to maintain and extend.
• Fix: Split the class into smaller, more focused classes. Use patterns like composition or delegation.

Before:

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public class UserManager {     
	public void createUser() { ... }     
	public void validateUser() { ... }     
	public void sendEmail() { ... }     
	public void logActivity() { ... } 
}

After:

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public class UserService {
	public void createUser() { ... } 
}
---
public class UserValidator {
	public void validateUser() { ... } 
}

---
public class EmailService {
	public void sendEmail() { ... } 
}

Magic Numbers and Strings

• The Smell: Unexplained hard-coded values scattered throughout your code.
• Why It’s Bad: Makes code confusing and harder to maintain.
• Fix: Replace them with constants or enums.

Before:

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if (status == 3) { ... }

After:

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private static final int STATUS_APPROVED = 3; 
...
...
if (status == STATUS_APPROVED) { ... }

Duplicate Code

• The Smell: Identical or nearly identical code blocks in multiple places.
• Why It’s Bad: Increases maintenance effort. Changes in one place need to be replicated everywhere.
• Fix: Abstract the duplicated logic into a reusable method or class.

Before:

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public int calculateDiscount(int price) {     
	return price * 10 / 100; 
} 

public int calculateTax(int price) {
	return price * 10 / 100; 
}

After:

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public int applyPercentage(int price, int percentage) {
	return price * percentage / 100; 
}

Long Parameter Lists

• The Smell: Methods or constructors take too many parameters.
• Why It’s Bad: Makes code harder to understand and prone to errors when calling.
• Fix: Use an object to encapsulate related parameters.

Before:

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public void createOrder(String product, int quantity, double price, String customerName, String address) { ... }

After:

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public void createOrder(OrderRequest request) { ... }

Tools to Detect Code Smells

1. SonarQube: Analyzes code quality and detects common smells.
2. IntelliJ IDEA: Built-in inspections flag potential issues like long methods or God objects.
3. Refactoring Books: Refactoring: Improving the Design of Existing Code by Martin Fowler is a must-read!

Actionable Tips to Avoid Code Smells

1. Start Small: Refactor one smell at a time.
2. Embrace Code Reviews: Fresh eyes can spot smells you’ve become blind to.
3. Automate Tests: Refactoring is less scary when you have a safety net of tests.
4. Follow SOLID Principles: Adhering to these can prevent many smells in the first place.

💡 Takeaway: Code smells are inevitable as your codebase grows, but catching and addressing them early can save you from costly rewrites later.