Retail Store Billing System

This project is a Retail Store Billing System developed in Java, created as part of an on-site coding assessment during a job interview. It was completed within one day and successfully led to a job offer. The solution demonstrates strong object-oriented design, clean code principles, and the ability to translate business rules into code efficiently under time pressure.

📌 Problem Statement

The task was to build a billing system that calculates the net payable amount for a customer after applying:

• User-based percentage discounts
• Flat discounts per $100 on the bill
• Category-based exclusions (e.g., no discount on groceries)

Discount Rules

1. Percentage-based discounts:

   • Employees get a 30% discount.
   • Affiliates get a 10% discount.
   • Customers who’ve been with the store for over 2 years get a 5% discount.
   • Groceries are excluded from percentage-based discounts.

2. Flat discount:

   • For every $100 on the total bill (after applying the percentage discount), a flat $5 discount is applied.

🧠 Key Features

• Clean object-oriented architecture using Java
• Polymorphism and inheritance for user roles (Employee, Affiliate, Customer)
• Enum usage for product categorization
• Unit tests with JUnit to validate business rules
• Introduced a ShoppingCart abstraction to manage cart entries and decouple billing logic from item management
• Simple logging utility and date calculation helper
• Clear separation of responsibilities across classes

🧪 Testing

Includes multiple unit tests using JUnit, covering scenarios such as:

• Discounts on groceries vs. non-groceries
• Combined percentage and flat discounts
• Behavior for different user roles and durations

📁 Project Structure

src/
├── com.company.retailstore
│   ├── Bill.java
│   ├── BillTest.java
│   ├── Customer.java
│   ├── Employee.java
│   ├── Affiliate.java
│   ├── ShoppingCart.java
│   ├── ShoppingCartEntry.java
│   ├── Product.java
│   ├── ProductType.java
│   ├── User.java
│   └── util/
│       ├── DateUtil.java
│       └── Log.java

🔧 Tech Stack

• Java
• JUnit 4

💡 Why This Project Matters

This repository highlights my ability to:

• Quickly understand business requirements and turn them into working code
• Apply OOP concepts to build a maintainable and extensible system
• Write logic that is easy to verify and test under real-world constraints

🛠️ Design Decisions

Although the original problem did not require a shopping cart system, I chose to introduce a ShoppingCart abstraction. This decision allowed for:

• A cleaner separation between billing and cart logic
• Better extensibility for future features like item removal or cart summaries
• A more realistic domain model that mirrors common retail systems

🙋 About This Project

This project was developed as part of an on-site coding assessment during a multi-stage interview process. The hiring journey included:

1. An initial HR interview
2. A technical interview at the company
3. An on-site coding assessment (this project)
4. A follow-up take-home coding assignment

I successfully completed all steps and received a job offer based on my performance across both coding assessments and interviews.

📜 License

This code is released under the MIT License.