Design Patterns in Java 🎓

An educational Maven project demonstrating various design patterns in Java with practical, real-world examples.

📋 Table of Contents

• Project Overview
• Prerequisites
• Project Structure
• Quick Start
• Running Instructions
• Testing
• Contributing

🎯 Project Overview

This project serves as an educational resource for learning design patterns through hands-on implementation. Each pattern is demonstrated with:

• ✅ Clear, practical examples
• ✅ Comprehensive documentation
• ✅ Interactive console demonstrations
• ✅ Unit tests
• ✅ Real-world use cases

🔧 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

design-patterns/
└── src/main/java/com/designpatterns/
    ├── creational/
    │   ├── factorymethod/
    │   ├── abstractfactory/
    │   ├── builder/
    │   └── prototype/
    ├── structural/
    │   ├── adapter/
    │   ├── bridge/
    │   ├── composite/
    │   ├── decorator/
    │   ├── facade/
    │   └── flyweight/
    └── behavioural/
        ├── observer/
        ├── command/
        ├── iterator/
        └── state/

Pattern Organization:

• Each design pattern has its own dedicated package
• Clean separation between domain objects and creation logic
• Extensible structure for adding new patterns
• Comprehensive test coverage for each pattern

🚀 Quick Start

1. Clone the Repository

git clone https://github.com/shift-elevate/design-patterns.git
cd design-patterns

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.designpatterns.Main"

This will launch the main demonstration showing all implemented design patterns.

📚 Running Instructions

🎯 Recommended: Run Main Application for Complete Demo

The best way to see all design patterns in action:

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

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

📦 Advanced: Build and Run JAR

For standalone execution:

# Build executable JAR
mvn clean package

# Run the JAR
java -jar target/design-patterns-1.0.0.jar

💻 IDE Integration

1. Import Project: Import as Maven project in your IDE
2. Set Java Version: Ensure Java 21 is configured
3. Run Main Class: Execute com.designpatterns.Main
4. Run Tests: Execute individual test classes for detailed pattern demonstrations

🧪 Testing

Run All Tests

mvn test

Run Specific Test Class

🏗️ Creational Patterns

# Factory Method Pattern
mvn test -Dtest=FactoryMethodTest

# Abstract Factory Pattern
mvn test -Dtest=AbstractFactoryTest

# Builder Pattern
mvn test -Dtest=BuilderPatternTest

# Prototype Pattern
mvn test -Dtest=PrototypePatternTest

🏛️ Structural Patterns

# Adapter Pattern
mvn test -Dtest=AdapterPatternTest

# Bridge Pattern
mvn test -Dtest=BridgePatternTest

# Composite Pattern
mvn test -Dtest=CompositePatternTest

# Decorator Pattern
mvn test -Dtest=DecoratorPatternTest

# Facade Pattern
mvn test -Dtest=FacadePatternTest

# Flyweight Pattern
mvn test -Dtest=FlyweightPatternTest

🎭 Behavioural Patterns

# Observer Pattern
mvn test -Dtest=ObserverPatternTest

# Command Pattern
mvn test -Dtest=CommandPatternTest

# Iterator Pattern
mvn test -Dtest=IteratorPatternTest

# State Pattern
mvn test -Dtest=StatePatternTest

🚀 Running Launcher Classes

Run Specific Launcher Class

🏗️ Creational Patterns

# Factory Method Pattern
mvn exec:java -Dexec.mainClass="com.designpatterns.creational.factorymethod.GameLauncher"

# Abstract Factory Pattern
mvn exec:java -Dexec.mainClass="com.designpatterns.creational.abstractfactory.GameLauncher"

# Builder Pattern
mvn exec:java -Dexec.mainClass="com.designpatterns.creational.builder.ECommerceLauncher"

# Prototype Pattern
mvn exec:java -Dexec.mainClass="com.designpatterns.creational.prototype.PrototypeLauncher"

🏛️ Structural Patterns

# Adapter Pattern
mvn exec:java -Dexec.mainClass="com.designpatterns.structural.adapter.ECommerceLauncher"

# Bridge Pattern
mvn exec:java -Dexec.mainClass="com.designpatterns.structural.bridge.BridgeLauncher"

# Composite Pattern
mvn exec:java -Dexec.mainClass="com.designpatterns.structural.composite.CompositeLauncher"

# Decorator Pattern
mvn exec:java -Dexec.mainClass="com.designpatterns.structural.decorator.CoffeeShopLauncher"

# Facade Pattern
mvn exec:java -Dexec.mainClass="com.designpatterns.structural.facade.CodeEditorClient"

# Flyweight Pattern
mvn exec:java -Dexec.mainClass="com.designpatterns.structural.flyweight.FlyweightLauncher"

🎭 Behavioural Patterns

# Observer Pattern
mvn exec:java -Dexec.mainClass="com.designpatterns.behavioural.observer.ObserverLauncher"

# Command Pattern
mvn exec:java -Dexec.mainClass="com.designpatterns.behavioural.command.SmartHomeLauncher"

# Iterator Pattern
mvn exec:java -Dexec.mainClass="com.designpatterns.behavioural.iterator.MusicPlayerLauncher"

# State Pattern
mvn exec:java -Dexec.mainClass="com.designpatterns.behavioural.state.DocumentWorkflowLauncher"

🐛 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.designpatterns.Main

📄 License

This project is created for educational purposes. Feel free to use and modify for learning.

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Happy Learning! 🚀

Remember: Understanding design patterns is about recognizing when and how to apply them, not just memorizing their structure.