Simple Invoice Generator

The Simple Invoice Generator is a Core Java–based billing application designed to demonstrate clean object-oriented design, inner classes, and file-based invoice generation. The system allows users to create itemized invoices, calculate billing totals, and export formatted invoice reports using Java file handling.

🔹 Overview

This project generates professional invoice files based on user input. It demonstrates key backend development concepts using pure Java, making it an ideal academic, portfolio, or interview project.

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🔹 Key Features

• Add items with name, price, and quantity
• Automatic calculation of:
  • Subtotal
  • Tax
  • Grand Total
• Inner class (Item) used inside Invoice
• Abstraction, Inheritance, Polymorphism, Encapsulation
• Clean file generation using Java File I/O
• Supports Online and Offline order workflows
• Extensible design suitable for integrating:
  • MySQL (JDBC)
  • GUI (JavaFX/Swing)
  • Spring Boot API

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🔹 Project Structure

src/
└── com.invoicegenerator
├── main
│   └── Main.java
├── model
│   ├── Order.java
│   ├── Invoice.java
│   ├── OnlineOrder.java
│   └── OfflineOrder.java
├── interfaces
│   └── Billable.java
└── utils
└── FileUtils.java

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🔹 Technologies Used

• Java (Core Java 8+)
• OOP Concepts
• File Handling (FileWriter, BufferedWriter)
• Collections Framework
• Command-Line UI

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🔹 How It Works

1. User runs the program from Main.java
2. Customer details and order type are collected
3. User adds multiple items with price and quantity
4. System calculates:
   • Subtotal
   • Tax
   • Grand Total
5. A formatted invoice .txt file is generated in the project directory
6. File name is auto-generated using timestamps

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🔹 Sample Invoice Output

===============================
INVOICE
=======

Customer : Babu
Order Type : Online
Payment Mode : UPI

Items:

1. Laptop (Qty: 1) - ₹55000
2. Mouse  (Qty: 1) - ₹500

Subtotal   : ₹55500
Tax (5%)   : ₹2775
Grand Total: ₹58275

Generated File: Babu_invoice_20250210_113045.txt

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🔹 Skills Demonstrated

• Object-Oriented Design
• Inner Class Implementation
• Interface-Based Architecture
• Clean File I/O Processing
• Modular Java Package Structure
• CLI-driven Application Workflow

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🔹 Author

Babu G V
Computer Science Engineering Student
Skills: Core Java, OOP, Collections, SQL, Spring, Spring Boot (Basics)
GitHub: Babugv2003

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🔹 Future Enhancements

• MySQL Database Integration (JDBC)
• REST API version using Spring Boot
• GUI Implementation using JavaFX
• PDF Invoice Export
• Cloud-based storage integration

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