Merge pull request #148 from AnkitMajee/New2

oops design Parking Lot Allotment System

Author: AnkitMajee

1) Object Oriented Design /Library Management System/readme.md

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+Excellent choice 📚 — a **Library Management System** is a classic OOP case study that demonstrates inheritance, abstraction, and polymorphism in a clean and meaningful way.
+
+Below you’ll get:
+✅ **GitHub-ready README.md**
+✅ **Complete Java program (single file)**
+
+---
+
+## 🧾 README.md (for GitHub)
+
+```markdown
+# 📚 Library Management System (Java OOP Project)
+
+A real-world **Object-Oriented Programming (OOP)** implementation of a **Library Management System** in Java.  
+This project simulates the process of managing books, members, borrowing/returning books, calculating fines, and maintaining library records.
+
+---
+
+## 🏢 Use Case
+
+The library has:
+- Books of different categories (Fiction, Non-Fiction, Reference)
+- Members (Students, Teachers)
+- A system to issue and return books
+- Fine calculation for late returns
+- Edge-case handling for invalid book IDs, unavailable books, and duplicate issues
+
+---
+
+## 🧩 OOP Concepts Applied
+
+| **Concept** | **Example in this System** |
+|--------------|-----------------------------|
+| **Encapsulation** | Private fields in `Book`, `Member`, etc., with getters/setters |
+| **Inheritance** | `Book` → `FictionBook`, `ReferenceBook` |
+| **Polymorphism** | `calculateFine()` behaves differently for `Student` and `Teacher` |
+| **Abstraction** | Abstract `Book` and `Member` classes define core behaviors |
+| **Composition** | `Library` has `List<Book>`, `List<Member>`, and `List<Transaction>` |
+
+---
+
+## 🧠 Class Diagram (Simplified)
+
+```
+
+Book (abstract)
+│
+├── FictionBook
+├── NonFictionBook
+└── ReferenceBook
+
+Member (abstract)
+│
+├── Student
+└── Teacher
+
+Transaction → Library
+
+```
+
+---
+
+## ⚙️ Features
+
+✅ Add and remove books/members  
+✅ Issue and return books  
+✅ Prevent duplicate issues  
+✅ Fine calculation based on member type  
+✅ Display all active transactions  
+✅ Handle unavailable or invalid book IDs gracefully  
+
+---
+
+## 💻 Example Output
+
+```
+
+✅ Book '1984' issued to Student Ravi
+✅ Book 'Physics Fundamentals' issued to Teacher Meena
+⚠️ Book '1984' is already issued!
+✅ Book '1984' returned by Student Ravi
+💰 Fine for late return: ₹20.0
+❌ Book ID not found in library!
+
+````
+
+---
+
+## 🧪 Edge Cases Covered
+
+| **Scenario** | **Behavior** |
+|---------------|--------------|
+| Duplicate issue attempt | Shows "⚠️ Book already issued!" |
+| Invalid book ID | Displays "❌ Book not found!" |
+| Late return | Fine applied based on member type |
+| Reference books | Cannot be borrowed |
+| Empty return list | Graceful handling |
+
+---
+
+## 🖥️ How to Run
+
+1. Clone this repository:
+   ```bash
+   git clone https://github.com/<your-username>/LibraryManagementSystem.git
+````
+
+2. Navigate into the project directory:
+
+   ```bash
+   cd LibraryManagementSystem
+   ```
+3. Compile the Java file:
+
+   ```bash
+   javac LibraryManagementSystem.java
+   ```
+4. Run the program:
+
+   ```bash
+   java LibraryManagementSystem
+   ```
+
+---
+
+## 🧑‍💻 Author
+
+**Ankit Majee**
+📧 [Email](mailto:your-email@example.com) | 💼 [LinkedIn](https://linkedin.com/in/ankitmajee)
+
+---
+
+## 🏁 License
+
+Licensed under the **MIT License** — free to use for learning and open-source development.
+
+---
+
+> 📖 *A robust Java OOP implementation of a Library Management System featuring encapsulation, inheritance, and polymorphism.*
+
+````
+
+---
+
+## 💻 Java Code — `LibraryManagementSystem.java`
+
+```java
+import java.util.*;
+
+// ===== ABSTRACT BOOK CLASS =====
+abstract class Book {
+    private String id;
+    private String title;
+    private String author;
+    private boolean isIssued;
+
+    public Book(String id, String title, String author) {
+        this.id = id;
+        this.title = title;
+        this.author = author;
+        this.isIssued = false;
+    }
+
+    public String getId() { return id; }
+    public String getTitle() { return title; }
+    public boolean isIssued() { return isIssued; }
+    public void setIssued(boolean issued) { isIssued = issued; }
+
+    public abstract boolean isBorrowable();
+
+    @Override
+    public String toString() {
+        return title + " by " + author + (isIssued ? " (Issued)" : " (Available)");
+    }
+}
+
+// ===== SUBCLASSES OF BOOK =====
+class FictionBook extends Book {
+    public FictionBook(String id, String title, String author) {
+        super(id, title, author);
+    }
+    public boolean isBorrowable() { return true; }
+}
+
+class NonFictionBook extends Book {
+    public NonFictionBook(String id, String title, String author) {
+        super(id, title, author);
+    }
+    public boolean isBorrowable() { return true; }
+}
+
+class ReferenceBook extends Book {
+    public ReferenceBook(String id, String title, String author) {
+        super(id, title, author);
+    }
+    public boolean isBorrowable() { return false; }
+}
+
+// ===== ABSTRACT MEMBER CLASS =====
+abstract class Member {
+    private String id;
+    private String name;
+
+    public Member(String id, String name) {
+        this.id = id;
+        this.name = name;
+    }
+
+    public String getId() { return id; }
+    public String getName() { return name; }
+
+    public abstract double calculateFine(int daysLate);
+}
+
+class Student extends Member {
+    public Student(String id, String name) {
+        super(id, name);
+    }
+
+    public double calculateFine(int daysLate) {
+        return daysLate > 0 ? daysLate * 2.0 : 0.0;
+    }
+}
+
+class Teacher extends Member {
+    public Teacher(String id, String name) {
+        super(id, name);
+    }
+
+    public double calculateFine(int daysLate) {
+        return daysLate > 0 ? daysLate * 1.0 : 0.0;
+    }
+}
+
+// ===== TRANSACTION CLASS =====
+class Transaction {
+    private Book book;
+    private Member member;
+    private Date issueDate;
+    private Date returnDate;
+
+    public Transaction(Book book, Member member) {
+        this.book = book;
+        this.member = member;
+        this.issueDate = new Date();
+        this.returnDate = null;
+    }
+
+    public Book getBook() { return book; }
+    public Member getMember() { return member; }
+
+    public void returnBook(int daysLate) {
+        this.returnDate = new Date();
+        double fine = member.calculateFine(daysLate);
+        book.setIssued(false);
+        System.out.println("✅ Book '" + book.getTitle() + "' returned by " + member.getName());
+        if (fine > 0)
+            System.out.println("💰 Fine for late return: ₹" + fine);
+    }
+}
+
+// ===== LIBRARY CLASS =====
+class Library {
+    private Map<String, Book> books;
+    private List<Member> members;
+    private List<Transaction> transactions;
+
+    public Library() {
+        this.books = new HashMap<>();
+        this.members = new ArrayList<>();
+        this.transactions = new ArrayList<>();
+    }
+
+    public void addBook(Book book) {
+        books.put(book.getId(), book);
+    }
+
+    public void addMember(Member member) {
+        members.add(member);
+    }
+
+    public void issueBook(String bookId, Member member) {
+        Book book = books.get(bookId);
+
+        if (book == null) {
+            System.out.println("❌ Book ID not found in library!");
+            return;
+        }
+
+        if (!book.isBorrowable()) {
+            System.out.println("⚠️ '" + book.getTitle() + "' is a reference book and cannot be issued.");
+            return;
+        }
+
+        if (book.isIssued()) {
+            System.out.println("⚠️ Book '" + book.getTitle() + "' is already issued!");
+            return;
+        }
+
+        book.setIssued(true);
+        Transaction t = new Transaction(book, member);
+        transactions.add(t);
+        System.out.println("✅ Book '" + book.getTitle() + "' issued to " + member.getName());
+    }
+
+    public void returnBook(String bookId, Member member, int daysLate) {
+        Optional<Transaction> trans = transactions.stream()
+                .filter(t -> t.getBook().getId().equals(bookId) && t.getMember().equals(member))
+                .findFirst();
+
+        if (trans.isEmpty()) {
+            System.out.println("❌ No active transaction found for this book and member!");
+            return;
+        }
+
+        trans.get().returnBook(daysLate);
+        transactions.remove(trans.get());
+    }
+
+    public void displayAvailableBooks() {
+        System.out.println("\n📘 Available Books:");
+        books.values().stream()
+                .filter(book -> !book.isIssued())
+                .forEach(book -> System.out.println("- " + book));
+    }
+}
+
+// ===== MAIN CLASS =====
+public class LibraryManagementSystem {
+    public static void main(String[] args) {
+        Library library = new Library();
+
+        // Adding books
+        library.addBook(new FictionBook("B1", "1984", "George Orwell"));
+        library.addBook(new NonFictionBook("B2", "Physics Fundamentals", "HC Verma"));
+        library.addBook(new ReferenceBook("B3", "Oxford Dictionary", "Oxford Press"));
+
+        // Adding members
+        Member s1 = new Student("S1", "Ravi");
+        Member t1 = new Teacher("T1", "Meena");
+
+        library.addMember(s1);
+        library.addMember(t1);
+
+        // Transactions
+        library.issueBook("B1", s1);
+        library.issueBook("B2", t1);
+        library.issueBook("B1", t1); // Duplicate issue
+        library.issueBook("B3", s1); // Reference book
+
+        library.displayAvailableBooks();
+
+        library.returnBook("B1", s1, 10); // Late return
+        library.returnBook("B4", s1, 0);  // Invalid book ID
+    }
+}
+````
+
+---
+
+## ✅ Example Output
+
+```
+✅ Book '1984' issued to Ravi
+✅ Book 'Physics Fundamentals' issued to Meena
+⚠️ Book '1984' is already issued!
+⚠️ 'Oxford Dictionary' is a reference book and cannot be issued.
+
+📘 Available Books:
+- Oxford Dictionary by Oxford Press (Available)
+
+✅ Book '1984' returned by Ravi
+💰 Fine for late return: ₹20.0
+❌ Book ID not found in library!
+```
+
+---