class Book {
  // Default values with parameterized constructor
  constructor(title = "Untitled", author = "Unknown", pages = 0) {
    this.title = title;
    this.author = author;
    this.pages = pages;
    this.isCheckedOut = false;
    this.createdAt = new Date();
  }

  getInfo() {
    return `'${this.title}' by ${this.author}`;
  }
}

const book1 = new Book("1984", "George Orwell", 328);
const book2 = new Book(); // Uses defaults
const book3 = new Book("The Hobbit"); // Partial parameters

console.log(book1.getInfo()); // "'1984' by George Orwell"
console.log(book2.title);     // "Untitled"
console.log(book3.title);     // "The Hobbit"
console.log(book3.author);    // "Unknown"

class DatabaseConnection {
  private connection: any;
  private isConnected: boolean = false;

  // Shorthand constructor — declares AND initializes properties
  constructor(
    private host: string,
    private port: number,
    private username: string,
    private password: string
  ) {}

  // Multiple constructors are NOT supported in TS/JS
  // Use static factory methods instead
  static createLocal(): DatabaseConnection {
    return new DatabaseConnection("localhost", 5432, "admin", "admin");
  }

  static fromConfig(config: { host: string; port: number }): DatabaseConnection {
    return new DatabaseConnection(config.host, config.port, "admin", "secret");
  }

  async connect(): Promise<void> {
    // Connection logic...
    this.isConnected = true;
  }
}

// Different ways to create instances
const db1 = new DatabaseConnection("prod.example.com", 5432, "user", "pass");
const db2 = DatabaseConnection.createLocal();

class Student:
    def __init__(self, name: str, student_id: int, grades: list[int] = None):
        """
        Constructor (__init__) for Student class.
        __init__ is NOT the constructor — it initializes after creation.
        __new__ is the actual constructor in Python.
        """
        self.name = name
        self.student_id = student_id
        self.grades = grades if grades is not None else []
        self.attendance = 0

    def __str__(self) -> str:
        return f"Student({self.name}, ID: {self.student_id})"

# Usage
alice = Student("Alice", 101, [85, 92, 78])
bob = Student("Bob", 102)  # grades defaults to []

print(alice)  # "Student(Alice, ID: 101)"

public class Rectangle {
    private double width;
    private double height;

    // Default constructor
    public Rectangle() {
        this(1.0, 1.0); // Constructor chaining
    }

    // Parameterized constructor
    public Rectangle(double width, double height) {
        // Validation in constructor
        if (width <= 0 || height <= 0) {
            throw new IllegalArgumentException("Dimensions must be positive");
        }
        this.width = width;
        this.height = height;
    }

    // Copy constructor
    public Rectangle(Rectangle other) {
        this(other.width, other.height);
    }

    public double area() { return width * height; }
}

// Usage
Rectangle r1 = new Rectangle();            // 1x1
Rectangle r2 = new Rectangle(5, 3);        // 5x3
Rectangle r3 = new Rectangle(r2);          // Copy of r2