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Clean Code in Java 🧹

An educational Maven project demonstrating common code smells and their refactoring solutions in Java with practical, real-world examples.

📋 Table of Contents

🎯 Project Overview

This project serves as an educational resource for learning clean code principles through hands-on examples. Each code smell is demonstrated with:

  • ✅ Before and after code comparisons
  • ✅ Interactive console demonstrations
  • ✅ Unit tests showing improvements

📋 Available Code Smells

Size & Complexity Problems

  • Long Method: Extract Method refactoring to break down complex methods
  • Long Parameter List: Introduce Parameter Object refactoring to group related parameters
  • Magic Numbers: Replace Magic Number with Named Constant refactoring to improve readability
  • Large Class: Extract Class refactoring to break down large classes into focused, single-responsibility classes
  • Data Clumps: Extract Class refactoring to group related data that always appear together into meaningful objects
  • Hardcoded Strings: Replace Magic String with Named Constant refactoring to centralize string management using typesafe enums
  • Primitive Obsession: Replace Primitive with Object refactoring to create rich domain models with meaningful types

OOP Anti-Patterns

  • Switch Statements: Replace Conditional with Polymorphism to eliminate switch statements
  • Temporary Field: Extract Class refactoring to organize instance variables only used in certain circumstances into dedicated classes

Dependency Problems

  • Feature Envy: Move Method refactoring to place methods with the data they operate on
  • Circular Dependencies: Dependency Inversion refactoring to break circular dependencies with interfaces

🔧 Prerequisites

  • Java 21 (OpenJDK 21.0.7+)
  • Maven 3.9+
  • IDE (IntelliJ IDEA, Eclipse, or VS Code recommended)

Installing Java 21

# Using SDKMAN (recommended)
sdk install java 21.0.7-tem

# For this project only (recommended approach)
# The project includes .sdkmanrc file for automatic environment switching
sdk env

# Or manually switch for this session only
sdk use java 21.0.7-tem

# Verify installation
java --version

📁 Project Structure

clean-code/
└── src/main/java/com/cleancode/
    ├── domain/
    ├── sizecomplexity/
    │   ├── longmethod/
    │   ├── longparameterlist/
    │   ├── magicnumbers/
    │   ├── largeclass/
    │   ├── dataclumps/
    │   ├── hardcodedstrings/
    │   └── primitiveobsession/
    ├── oopantipatterns/
    │   ├── switchstatements/
    │   └── temporaryfield/
    ├── dependencyproblems/
    │   ├── featureenvy/
    │   └── circulardependencies/
    └── Main.java

Code Smell Organization:

  • Each code smell has its own dedicated package
  • Clear separation between problematic and refactored code
  • Shared domain models in com.cleancode.domain package
  • Comprehensive test coverage for each smell

🚀 Quick Start

1. Clone the Repository

git clone https://github.com/shift-elevate/clean-code.git
cd clean-code

2. Setup Environment (Automatic with SDKMAN)

The project includes a .sdkmanrc file that automatically configures Java 21 and Maven when you enter the directory:

# Activate the project environment (Java 21 + Maven)
sdk env

# This will automatically switch to:
# - Java 21.0.7-tem
# - Maven 3.9.10

3. Build the Project

mvn clean compile

4. Run the Main Application

mvn exec:java -Dexec.mainClass="com.cleancode.Main"

This will launch the main demonstration showing all implemented code smells and their refactored solutions.

📚 Running Instructions

🎯 Recommended: Run Main Application for Complete Demo

The best way to see all code smells and refactoring solutions in action:

# Run the main application with all demonstrations
mvn exec:java -Dexec.mainClass="com.cleancode.Main"

# Or compile and run directly
mvn clean compile
java -cp target/classes com.cleancode.Main

📦 Advanced: Build and Run JAR

For standalone execution:

# Build executable JAR
mvn clean package

# Run the JAR
java -jar target/clean-code-java-1.0.0.jar

🧪 Testing

Run All Tests

mvn test

Run Individual Code Smell Demonstrations

# Long Method Code Smell
mvn exec:java@long-method

# Switch Statements Code Smell
mvn exec:java@switch-statements

# Primitive Obsession Code Smell
mvn exec:java@primitive-obsession

# Long Parameter List Code Smell
mvn exec:java@long-parameter-list

# Magic Numbers Code Smell
mvn exec:java@magic-numbers

# Large Class Code Smell
mvn exec:java@large-class

# Data Clumps Code Smell
mvn exec:java@data-clumps

# Hardcoded Strings Code Smell
mvn exec:java@hardcoded-strings

# Feature Envy Code Smell
mvn exec:java@feature-envy

# Circular Dependencies Code Smell
mvn exec:java@circular-dependencies

# Temporary Field Code Smell
mvn exec:java@temporary-field

Note: Each execution ID runs only the specific code smell demonstration, not all of them.

Run All Code Smells Together

# Run the main application with all demonstrations
mvn exec:java -Dexec.mainClass="com.cleancode.Main"

Run Specific Test Class

# Long Method Code Smell
mvn test -Dtest=LongMethodTest

# Long Parameter List Code Smell
mvn test -Dtest=LongParameterListTest

# Magic Numbers Code Smell
mvn test -Dtest=MagicNumbersTest

# Large Class Code Smell
mvn test -Dtest=LargeClassTest

# Data Clumps Code Smell
mvn test -Dtest=DataClumpsTest

# Hardcoded Strings Code Smell
mvn test -Dtest=HardcodedStringsTest

# Switch Statements Code Smell
mvn test -Dtest=SwitchStatementsTest

# Primitive Obsession Code Smell
mvn test -Dtest=PrimitiveObsessionTest

# Feature Envy Code Smell
mvn test -Dtest=FeatureEnvyTest

# Circular Dependencies Code Smell
mvn test -Dtest=CircularDependenciesTest

# Temporary Field Code Smell
mvn test -Dtest=TemporaryFieldTest

🐛 Troubleshooting

Common Issues

Java Version Issues:

# Check Java version
java --version

# Ensure Java 21 is active
sdk current java

Maven Compilation Issues:

# Clean and rebuild
mvn clean compile

# Skip tests if needed
mvn compile -DskipTests

Class Path Issues:

# Ensure proper classpath when running
java -cp target/classes com.cleancode.Main