📚 Library Management System (OOP Showcase)

A clean, modular Java console application designed to practice Object-Oriented Programming best practices, specifically Encapsulation and the Single Responsibility Principle.

📖 Overview

This project simulates the core operations of a physical library. Unlike basic "Hello World" scripts, this application separates the Data Layer (Book), Logic Layer (Library), and Presentation Layer (LibraryApp) to simulate a real-world software architecture.

It demonstrates how to manage in-memory state, handle user input validation, and manipulate relationships between objects.

🏗️ Architecture & Design

The project follows a "Separation of Concerns" philosophy:

• Book.java (Model): A POJO (Plain Old Java Object) using Encapsulation (private fields, public getters/setters) to protect data integrity.
• Library.java (Service): Manages the business logic. It handles the ArrayList collection and uses static variables to track global inventory state.
• LibraryApp.java (View/Controller): Handles the UI (Console) and User Input (Scanner), keeping the core logic clean of print statements.

Class Diagram

classDiagram
    class Book {
        -String id
        -String title
        -int stock
        +getId()
        +setStock()
    }
    class Library {
        -ArrayList~Book~ books
        -static int totalBooks
        +addBook(Book)
        +lendBook(String id)
        +searchBook(String id)
    }
    class LibraryApp {
        -Library library
        -Scanner scanner
        +start()
        -showMenu()
        -handleOptions()
    }

    LibraryApp --> Library : uses
    Library o-- Book : manages

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🚀 Key Features

• Inventory Management: Dynamic addition of books using ArrayList.
• Stock Tracking: Real-time updates to global book counts using static properties.
• Lending System: Logic to decrease stock upon lending and validate availability.
• Search: ID-based lookup algorithms.

🛠️ Technical Concepts Applied

• Encapsulation: All class attributes are private; access is controlled via methods.
• Polymorphism: Overriding the toString() method for clean object visualization.
• State Management: Using static to maintain counters across the application lifecycle.
• Input Handling: Robust use of java.util.Scanner for interactive menus.

💻 How to Run

1. Clone the repository:

git clone https://github.com/huderdcv/java-oop-library-system.git

2. Compile the source:

javac library/*.java

3. Run the Main class:

java library.Main