🛒 Java E-Shop System

Advanced e-commerce simulation demonstrating object-oriented programming principles and complex business logic implementation in Java.

🚀 Features

• Product Management - Electronics, Books, Clothing with different behaviors
• Shopping Cart System - Add, remove, quantity management
• Dynamic Pricing - Quantity-based and seasonal discounts
• Smart Shipping - Category-based shipping cost calculation
• Discount Interface - Flexible discount system implementation
• Polymorphic Collections - Single cart managing multiple product types

Demo Output

===Nákupní košík===
Laptop (Electronics) - 1x 25000.0 Kč
Tričko (Clothing) - 2x 500.0 Kč
Java Programming (Books) - 6x 800.0 Kč

===Po aplikaci slev===
Laptop (Electronics) - 1x 22500.0 Kč (seasonal 10% discount)
Tričko (Clothing) - 2x 500.0 Kč (no discounts)
Java Programming (Books) - 6x 680.0 Kč (quantity + seasonal discounts)

Poštovné: 280 Kč
Celková cena: 26960 Kč

🛠️ Technologies Used

• Java 17+ - Core programming language
• Advanced OOP - Inheritance, Polymorphism, Abstract classes
• Interface Design - Discountable interface for flexible pricing
• Collections Framework - ArrayList with polymorphic object storage
• Business Logic - Real-world e-commerce calculations

Architecture Overview

📁 E-Shop System
├── 📄 Product.java (Abstract base class)
├── 📄 Electronics.java (Extends Product, implements Discountable)
├── 📄 Books.java (Extends Product, implements Discountable)
├── 📄 Clothing.java (Extends Product only)
├── 📄 Discountable.java (Interface for discount behavior)
├── 📄 ShoppingCart.java (Cart management with polymorphism)
└── 📄 Main.java (Application entry point)

🎯 Key OOP Concepts Demonstrated

Inheritance Hierarchy

Product (Abstract)
├── Electronics implements Discountable
├── Books implements Discountable  
└── Clothing (no discounts)

Polymorphism in Action

ArrayList<Product> products = new ArrayList<>();
// Can store Electronics, Books, Clothing objects
// Each behaves differently for shipping and discounts

Interface Implementation

public interface Discountable {
    double calculateDiscount(int quantity);
    void applySeasonalDiscount();
}

How to Run

Clone the repository

git clone https://github.com/JinderO/eshop-system-java.git
cd eshop-system-java

Compile the project

javac -d bin src/dev/jov/*.java

Run the application

java -cp bin dev.jov.Main

Business Logic Implementation

Product Categories with Different Shipping

• Electronics: 150 Kč shipping + seasonal discounts
• Books: 50 Kč shipping + quantity discounts (5+ items = 10% off)
• Clothing: 80 Kč shipping + no discounts

Smart Discount System

• Quantity Discounts: Automatic for eligible products
• Seasonal Discounts: Applied independently
• Interface-based: Easy to extend with new discount types

What I Learned

• Abstract Classes vs Interfaces - When to use each approach
• Polymorphic Collections - Managing different object types uniformly
• Interface Segregation - Not all products need all behaviors
• Business Logic Modeling - Translating real-world rules into code
• Flexible Design Patterns - Easy to add new product types or discounts

Code Highlights

Polymorphic Cart Management:

public double calculateTotal() {
    double total = 0;
    for (int i = 0; i < products.size(); i++) {
        Product product = products.get(i);
        int quantity = quantities.get(i);
        total += (product.getPrice() * quantity) + product.calculateShipping();
    }
    return total;
}

Interface-based Discount Application:

public void applyDiscounts() {
    for (Product product : products) {
        if (product instanceof Discountable) {
            ((Discountable) product).applySeasonalDiscount();
        }
    }
}

Potential Extensions

• Add user authentication system
• Implement order persistence to database
• Create web interface with Spring Boot
• Add payment processing simulation
• Implement inventory management
• Add product search and filtering

👨‍💻 Author

Jindřich Ovádek - Java Developer in Training - @JinderO

Technical Achievements

• Advanced OOP Mastery - Demonstrates sophisticated understanding of inheritance and polymorphism
• Interface Design Excellence - Clean separation of concerns with flexible discount system
• Complex Business Logic - Real-world e-commerce calculations and rule implementation
• Scalable Architecture - Extensible design patterns for future enhancements
• Polymorphic Collections - Professional management of diverse object types in unified structures

This project showcases advanced Java programming skills including inheritance hierarchies, interface design, polymorphic collections, and complex business logic implementation typical of real-world e-commerce systems. The implementation demonstrates enterprise-level thinking and scalable design patterns.