clean-code

Clean Code Skill

Write readable, maintainable code following Clean Code principles.

When to Use

• User says "clean this code" / "refactor" / "improve readability"
• Code review focusing on maintainability
• Reducing complexity
• Improving naming

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Core Principles

Principle	Meaning	Violation Sign
DRY	Don't Repeat Yourself	Copy-pasted code blocks
KISS	Keep It Simple, Stupid	Over-engineered solutions
YAGNI	You Aren't Gonna Need It	Features "just in case"

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DRY - Don't Repeat Yourself

"Every piece of knowledge must have a single, unambiguous representation in the system."

Violation

// ❌ BAD: Same validation logic repeated
public class UserController {

    public void createUser(UserRequest request) {
        if (request.getEmail() == null || request.getEmail().isBlank()) {
            throw new ValidationException("Email is required");
        }
        if (!request.getEmail().contains("@")) {
            throw new ValidationException("Invalid email format");
        }
        // ... create user
    }

    public void updateUser(UserRequest request) {
        if (request.getEmail() == null || request.getEmail().isBlank()) {
            throw new ValidationException("Email is required");
        }
        if (!request.getEmail().contains("@")) {
            throw new ValidationException("Invalid email format");
        }
        // ... update user
    }
}

Refactored

// ✅ GOOD: Single source of truth
public class EmailValidator {

    public void validate(String email) {
        if (email == null || email.isBlank()) {
            throw new ValidationException("Email is required");
        }
        if (!email.contains("@")) {
            throw new ValidationException("Invalid email format");
        }
    }
}

public class UserController {
    private final EmailValidator emailValidator;

    public void createUser(UserRequest request) {
        emailValidator.validate(request.getEmail());
        // ... create user
    }

    public void updateUser(UserRequest request) {
        emailValidator.validate(request.getEmail());
        // ... update user
    }
}