// ES6 Class Syntax
class Person {
  // Constructor — called when creating a new instance
  constructor(name, age) {
    this.name = name;
    this.age = age;
  }

  // Method
  greet() {
    return `Hi, I'm ${this.name} and I'm ${this.age} years old.`;
  }

  // Getter
  get birthYear() {
    return new Date().getFullYear() - this.age;
  }

  // Setter
  set birthYear(year) {
    this.age = new Date().getFullYear() - year;
  }

  // Static method — called on the class itself, not instances
  static createAnonymous() {
    return new Person("Anonymous", 0);
  }
}

const john = new Person("John", 30);
console.log(john.greet()); // "Hi, I'm John and I'm 30 years old."
console.log(john.birthYear); // 1994
john.birthYear = 1990;
console.log(john.age); // 34

const anonymous = Person.createAnonymous();

// TypeScript adds type annotations and access modifiers
class Employee {
  // Access modifiers: public (default), private, protected
  public name: string;
  private salary: number;
  protected department: string;

  constructor(name: string, salary: number, department: string) {
    this.name = name;
    this.salary = salary;
    this.department = department;
  }

  // Shorthand constructor (TypeScript)
  // constructor(
  //   public name: string,
  //   private salary: number,
  //   protected department: string
  // ) {}

  public getSalary(): number {
    return this.salary;
  }

  public work(): string {
    return `${this.name} is working in ${this.department}`;
  }
}

const emp = new Employee("Alice", 75000, "Engineering");
console.log(emp.name); // "Alice"
// console.log(emp.salary); // ❌ Error: Property 'salary' is private
console.log(emp.getSalary()); // 75000

class Book:
    # Class variable — shared by all instances
    total_books = 0

    # Constructor
    def __init__(self, title: str, author: str, pages: int):
        # Instance variables
        self.title = title
        self.author = author
        self.pages = pages
        Book.total_books += 1

    # Instance method
    def description(self) -> str:
        return f"'{self.title}' by {self.author}, {self.pages} pages"

    # Class method
    @classmethod
    def create_empty(cls) -> 'Book':
        return cls("Unknown", "Unknown", 0)

    # Static method
    @staticmethod
    def is_valid_title(title: str) -> bool:
        return len(title) > 0 and len(title) < 200


book1 = Book("1984", "George Orwell", 328)
book2 = Book("To Kill a Mockingbird", "Harper Lee", 281)
print(book1.description())  # "'1984' by George Orwell, 328 pages"
print(Book.total_books)     # 2

// Java — explicit and strongly-typed
public class Student {
    // Fields
    private String name;
    private int id;
    private double gpa;

    // Constructor
    public Student(String name, int id) {
        this.name = name;
        this.id = id;
        this.gpa = 0.0;
    }

    // Methods
    public void setGpa(double gpa) {
        if (gpa >= 0.0 && gpa <= 4.0) {
            this.gpa = gpa;
        }
    }

    public double getGpa() {
        return this.gpa;
    }

    public String getGrade() {
        if (gpa >= 3.7) return "A";
        if (gpa >= 2.7) return "B";
        if (gpa >= 1.7) return "C";
        return "D";
    }

    // Static method
    public static Student createFreshman(String name, int id) {
        return new Student(name, id);
    }
}