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Design Patterns in Java 🎓

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

📋 Table of Contents

🎯 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/
    │   └── singleton/
    ├── structural/
    │   ├── adapter/
    │   ├── bridge/
    │   ├── composite/
    │   ├── decorator/
    │   ├── facade/
    │   ├── flyweight/
    │   └── proxy/
    └── behavioural/
        ├── observer/
        ├── command/
        ├── iterator/
        ├── state/
        ├── mediator/
        ├── strategy/
        ├── chainofresponsibility/
        ├── memento/
        └── visitor/

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

# Singleton Pattern
mvn test -Dtest=SingletonPatternTest

🏛️ 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

# Proxy Pattern
mvn test -Dtest=ProxyPatternTest

🎭 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

# Mediator Pattern
mvn test -Dtest=MediatorPatternTest

# Strategy Pattern
mvn test -Dtest=StrategyPatternTest

# Chain of Responsibility Pattern
mvn test -Dtest=ChainOfResponsibilityPatternTest

# Memento Pattern
mvn test -Dtest=MementoPatternTest

# Visitor Pattern
mvn test -Dtest=VisitorPatternTest

🚀 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"

# Singleton Pattern
mvn exec:java -Dexec.mainClass="com.designpatterns.creational.singleton.SingletonLauncher"

🏛️ 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"

# Proxy Pattern
mvn exec:java -Dexec.mainClass="com.designpatterns.structural.proxy.ProxyLauncher"

🎭 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"

# Mediator Pattern
mvn exec:java -Dexec.mainClass="com.designpatterns.behavioural.mediator.MediatorLauncher"

# Strategy Pattern
mvn exec:java -Dexec.mainClass="com.designpatterns.behavioural.strategy.NavigationLauncher"

# Chain of Responsibility Pattern
mvn exec:java -Dexec.mainClass="com.designpatterns.behavioural.chainofresponsibility.ExpenseApprovalLauncher"

# Memento Pattern
mvn exec:java -Dexec.mainClass="com.designpatterns.behavioural.memento.DiagramEditorLauncher"

# Visitor Pattern
mvn exec:java -Dexec.mainClass="com.designpatterns.behavioural.visitor.ClinicBillingLauncher"

🐛 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.

Happy Learning! 🚀

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

About

Demonstration of various design patterns in Java with practical, real-world examples with comprehensive tests and executable code samples.

newsletter.shiftelevate.dev/

Topics

java design-patterns observer-pattern educational strategy-pattern builder-pattern software-architecture factory-pattern abstract-factory-pattern adapter-pattern singleton-pattern bridge-pattern decorator-pattern facade-pattern behavioral-patterns creational-patterns prototype-pattern flyweight-pattern structural-patterns composite-pattern

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