Inventory & Sales Management System (3-Layer Architecture)

This project is a desktop application developed as a portfolio piece to demonstrate proficiency in Java Desktop Development. It focuses on the practical application of software engineering fundamentals, such as 3-layer architecture, DAO patterns, and OOP principles.

🎯 Project Purpose

The goal of this system is to manage a basic commercial workflow (Categories -> Products -> Sales/Purchases) while maintaining a clean, decoupled codebase that goes beyond basic scripting.

🛠️ Tech Stack

• Language: Java (OpenJDK)
• GUI: Java Swing (MDI - Multiple Document Interface)
• Database: MySQL via JDBC
• Design Patterns: DAO (Data Access Object) & Singleton
• IDE: NetBeans

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🏗️ Software Architecture & SOLID Principles

To ensure the code is organized and professional, I applied several engineering principles:

Architecture Layers

• Presentacion: UI logic using JInternalFrame and event handling.
• Negocio: Intermediate layer for data validation and business rules.
• Datos: Implementation of CRUD operations using the DAO pattern.
• Entidades: Encapsulated classes (POJOs) representing the domain model.

Technical Principles Applied

Principle	Implementation in this Project
Encapsulation	Private attributes and public getters/setters in all entidades to protect data integrity.
Abstraction	Use of Interfaces in datos.interfaces to decouple business logic from data access.
Single Responsibility (SRP)	Specific classes for DB connection, data access, and UI logic, avoiding "God Classes".
Interface Segregation	Using specific interfaces so that classes only implement the methods they truly need.

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🚀 Key Learning Milestones

1. Relational Database Mapping: Managed one-to-many relationships and SQL joins for transactions.
2. Logical Deletion: Implementing "Active/Inactive" status toggles instead of hard-deleting records to maintain audit trails.
3. Advanced Swing UI: Building a professional MDI (Multiple Document Interface) using JDesktopPane.
4. Decoupled Design: Ensuring the negocio layer communicates with datos through contracts (interfaces).

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💬 Technical Q&A (Interview Readiness)

Q: Why use a 3-layer architecture instead of putting all logic in the UI? A: To ensure maintenance and scalability. By separating the UI, Business Logic, and Data Access, I can modify the database schema or the interface without breaking the entire system.

Q: What is the benefit of the DAO (Data Access Object) pattern here? A: It abstracts the data persistence logic. If the project needs to switch from MySQL to another database in the future, I only need to change the implementation in the datos layer; the rest of the application remains untouched.

Q: Why did you use Interfaces in the datos.interfaces package? A: To apply "Program to an interface, not an implementation." This allows for loose coupling and makes the code easier to test and extend by defining clear contracts for what each DAO should do.

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⚙️ Setup

1. Database: Import the provided .sql script into your MySQL server.
2. Configuration: Update the database/Conexion.java file with your local credentials.
3. Compile: Open the project in NetBeans and run the main class in the presentacion package.

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Note: This project was developed as a final product for a Java Programming Course. It is intended for educational and portfolio demonstration purposes, highlighting the use of clean architecture and OOP.

📄 License

This project is distributed under the MIT license. Its purpose is strictly educational and research-related.

Author: JUAN S. Contact: https://github.com/johnyse99