Design Patterns Project: Inventory Management System (Java & Frontend Sim)

This project demonstrates the integration of six critical design patterns into a console-based inventory management application developed in Java, featuring a modern Single Page Application (SPA) simulation for the frontend.

Core Architecture and Frontend Enhancements

• Backend: Developed in Java, incorporating Composite, Decorator, Observer, Strategy, Singleton, and Builder patterns.
• Frontend (SPA): Built using HTML, CSS, and JavaScript. The UI simulates a modern SPA by using the fetch API to load content dynamically into the main area (#content-container) upon menu selection.
• Scope Resolution: All interaction functions (simulateAddCategory, simulateStrategy, etc.) are defined in the global scope (index.html) to prevent JavaScript ReferenceError issues caused by dynamic page loading.

Integrated Design Patterns Summary

Pattern	Category	Role in Application
Composite	Structural	Manages the hierarchy between Categories and Products.
Decorator	Structural	Dynamically adds price adjustments (e.g., discount/markup) to products.
Observer	Behavioral	Monitors stock levels and triggers alerts upon changes (Low Stock).
Strategy	Behavioral	Enables dynamic switching of pricing logic (Normal vs. Tax Included).
Singleton	Creational	Manages global application settings (ConfigurationManager) centrally.
Builder	Creational	Provides controlled, step-by-step creation for complex products (e.g., Laptops).

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How to Run the Project

The application requires running the Java Backend and the Web Frontend processes concurrently.

Step 1: Run the Java Backend (Core Logic)

This process runs the core application logic and outputs all logs and alerts.

1. In your command line, navigate to the backend directory.
2. Compile all Java source files:

   javac *.java

3. Start the main application (Core Logic):

   java Main

   (Keep this console window open; all logs, alerts, and pattern outputs will appear here.)

Step 2: Run the Frontend Server (SPA)

The web frontend must be served over HTTP to allow JavaScript fetch API calls to work correctly (bypassing local file security restrictions).

1. Open a new command line window and navigate to the backend directory (where SimpleHttpServer.java is located).
2. Start the Frontend Server:

   java SimpleHttpServer

3. Open your browser and navigate to the application address:

   http://localhost:8000/index.html
   

You can now interact with the web interface, and the resulting actions will simulate signals being sent to your running Java console.