🛒 ShopWise — Java OOP E-Commerce Demo

A Java console application demonstrating core Object-Oriented Programming principles through a simulated e-commerce system. Built as a portfolio project to showcase clean, maintainable, and scalable software design.

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🎯 OOP Concepts Demonstrated

1. Encapsulation

All fields in Product, CartItem, and ShoppingCart are private. Access is controlled through getters and setters that enforce business rules (e.g. price cannot be negative, stock cannot go below zero).

public void setPrice(double price) {
    if (price < 0) throw new IllegalArgumentException("Price cannot be negative.");
    this.price = price;
}

2. Inheritance

Electronics, Clothing, and Food all extend the abstract Product class. They inherit shared behaviour (stock management, toString base) and add their own fields.

Product (abstract)
├── Electronics  (brand, warrantyMonths)
├── Clothing     (size, colour)
└── Food         (expiryDate, isOrganic)

3. Polymorphism

Each subclass overrides applyDiscount() and getCategory() with its own logic:

Product Type	Discount
Electronics	10% off
Clothing	20% off
Food (Organic)	5% off
Food (Regular)	15% off

The ShoppingCart calls applyDiscount() on a Product reference — the correct subclass method runs automatically.

4. Abstraction

Product is an abstract class. It defines the contract (getCategory(), applyDiscount()) but leaves the implementation to each subclass.

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📂 Project Structure

src/
└── main/java/com/example/ecommerce/
    ├── Main.java                        # Entry point
    ├── model/
    │   ├── Product.java                 # Abstract base class
    │   ├── Electronics.java             # Inherits Product
    │   ├── Clothing.java                # Inherits Product
    │   ├── Food.java                    # Inherits Product
    │   ├── CartItem.java                # Encapsulates cart line item
    │   └── Discountable.java            # Interface (polymorphism)
    └── service/
        ├── ProductCatalogue.java        # Manages product inventory
        └── ShoppingCart.java            # Manages cart operations

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🚀 Getting Started

Prerequisites

• Java 11 or higher
• Any Java IDE (IntelliJ IDEA, Eclipse, VS Code with Java extension)

Run the project

1. Clone the repository:

   git clone https://github.com/Bothokakula/shopwise-oop-java.git

2. Open in your IDE and run Main.java, or compile via terminal:

   cd src/main/java
   javac com/example/ecommerce/**/*.java com/example/ecommerce/Main.java
   java com.example.ecommerce.Main

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🧾 Sample Output

===== PRODUCT CATALOGUE =====
[E001] Samsung Galaxy Book | Category: Electronics | Price: R15999.99 | Stock: 10 | Brand: Samsung | Warranty: 24 months
[C001] Levi's Denim Jacket | Category: Clothing | Price: R1299.99 | Stock: 50 | Size: L | Colour: Indigo Blue
...

===== SALE PRICES =====
Samsung Galaxy Book          Original: R15999.99  ->  Sale: R14399.99
Levi's Denim Jacket          Original: R1299.99   ->  Sale: R1039.99
...

========================================
       SHOPWISE — ORDER RECEIPT
========================================
Customer ID: CUST-001
...
Discounted Total: R16842.45
========================================

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🛠️ Tech Stack

Language	Java 11+
Paradigm	Object-Oriented Programming
IDE	IntelliJ IDEA / VS Code

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