Java Projects ☕

A collection of Java console applications developed during my training at Coding Factory (AUEB). These projects demonstrate my progression from basic syntax to more complex Object-Oriented Design patterns and Data Structures.

🚀 Featured Projects (in src/projects)

1. Library Management System (New!)

Focus: Separation of Concerns, Java Streams, Service Layer Pattern

A robust library simulation that manages books, members, and loans completely in-memory. This project represents a step up in architecture, separating the User Interface (Console) from the Business Logic.

• Architecture: Separation of UI (Main), Service (Logic), and Domain (Entities).
• Key Features:
  • Smart Loan System: Prevents borrowing if copies are unavailable or user validation fails.
  • Java Streams: Used extensively for filtering (searching books) and sorting (listing active loans by due date).
  • Robust Validation: Inputs are protected against crashes; ISBNs and Dates are handled logically.
  • Logic: Calculates available copies dynamically based on active loans (Single Source of Truth).

2. Contact Book

Focus: CRUD Operations, Data Structures (Maps), Input Validation

A functional address book application that allows users to manage their contacts efficiently.

• Algorithms: Uses HashMap Indexing to search for phone numbers in O(1) time (instant lookup) rather than looping through lists.
• Validation: Strict Regex validation for E.164 phone formats and email addresses.
• Features: Add, Search (by name prefix or phone), Update, and Delete contacts.

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🕹️ Mini Apps (in src/mini_apps)

Smaller exercises focused on specific logic challenges:

• Guess Game: A number guessing game implementing "lives" and retry logic.
• Entry System: Logic gates for age checks and VIP access control.
• FizzBuzz: The classic coding interview question implementation.

🛠️ Tech Stack

• Language: Java 21 (Amazon Corretto)
• Concepts: OOP (Encapsulation, Polymorphism), Java Streams API, Collections Framework (List, Map, Set).
• Tools: IntelliJ IDEA, Git & GitHub.

📂 Project Structure

The repository is organized into two main categories:

Java-Projects/
└── src/
    ├── mini_apps/             # Logic puzzles & basic exercises
    │   ├── EntrySystem
    │   ├── FizzBuzz
    │   └── GuessGame
    │
    └── projects/              # Full-featured applications
        ├── contactbook/       # HashMap & CRUD demo
        └── librarymanagement/ # Advanced architecture demo
            ├── domain/        # Entities (Book, Loan, Member)
            ├── service/       # Business Logic (LibraryService)
            └── ui/            # Entry point (LibraryApp)

🏃 How to Run

1. Clone the repository.
2. Open the folder in IntelliJ IDEA.
3. Navigate to the entry point: src/projects/librarymanagement/ui/LibraryApp.java
4. Right-click the class file and select Run.

Created by Giannis as part of the Coding Factory curriculum.