06-classes.ts

// ============================================
// 06. Classes
// ============================================

// Basic Class
class Person {
  name: string;
  age: number;

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

  greet(): string {
    return `Hello, I'm ${this.name} and I'm ${this.age} years old.`;
  }
}


const person = new Person("Alice", 25);
console.log(person.greet());

// Access Modifiers
class BankAccount {
  private balance: number = 0;

  deposit(amount: number): void {
    this.balance += amount;
  }

  getBalance(): number {
    return this.balance;
  }
}

const account = new BankAccount();
account.deposit(100);
// account.balance; // Error: Property 'balance' is private
console.log(account.getBalance()); // OK

// Protected
class Animal {
  protected name: string;

  constructor(name: string) {
    this.name = name;
  }
}

class Dog extends Animal {
  bark(): void {
    console.log(`${this.name} barks!`); // OK, name is protected
  }
}

const dog = new Dog("Buddy");
// dog.name; // Error: Property 'name' is protected
dog.bark();

// Readonly
class PersonReadonly {
  readonly id: number;
  name: string;

  constructor(id: number, name: string) {
    this.id = id;  // OK, setting during initialization
    this.name = name;
  }
}

const person2 = new PersonReadonly(1, "Alice");
// person2.id = 2; // Error: Cannot assign to 'id' because it is a read-only property

// Parameter Properties
class PersonParam {
  constructor(public name: string, public age: number) {
    // Automatically creates and assigns this.name and this.age
  }
  constructor(public name: string, public age: number, public email: string ) {
    // Automatically creates and assigns this.name and this.age and this.email
  }
}

const person3 = new PersonParam("Alice", 25);
console.log(person3.name, person3.age, person3.email);

// Getters and Setters
class Temperature {
  private _celsius: number = 0;

  get celsius(): number {
    return this._celsius;
  }

  set celsius(value: number) {
    if (value < -273.15) {
      throw new Error("Temperature cannot be below absolute zero");
    }
    this._celsius = value;
  }

  get fahrenheit(): number {
    return this._celsius * 9/5 + 32;
  }

  set fahrenheit(value: number) {
    this.celsius = (value - 32) * 5/9;
  }
}

const temp = new Temperature();
temp.celsius = 25;
console.log(temp.fahrenheit); // 77

// Inheritance
class AnimalBase {
  name: string;

  constructor(name: string) {
    this.name = name;
  }

  move(distance: number = 0): void {
    console.log(`${this.name} moved ${distance}m.`);
  }
}

class DogInherit extends AnimalBase {
  breed: string;

  constructor(name: string, breed: string) {
    super(name);  // Call parent constructor
    this.breed = breed;
  }

  bark(): void {
    console.log("Woof! Woof!");
  }
}

const dog2 = new DogInherit("Buddy", "Golden Retriever");
dog2.move(10);  // Inherited method
dog2.bark();    // Dog-specific method

// Abstract Classes
abstract class AnimalAbstract {
  name: string;

  constructor(name: string) {
    this.name = name;
  }

  abstract makeSound(): void;  // Must be implemented by subclasses

  move(): void {
    console.log(`${this.name} is moving.`);
  }
}

class DogAbstract extends AnimalAbstract {
  makeSound(): void {
    console.log("Woof!");
  }
}

// const animal = new AnimalAbstract("Generic"); // Error: Cannot create instance of abstract class
const dog3 = new DogAbstract("Buddy");
dog3.makeSound();

// Static Members
class MathHelper {
  static PI: number = 3.14159;

  static add(a: number, b: number): number {
    return a + b;
  }
}

console.log(MathHelper.PI);        // 3.14159
console.log(MathHelper.add(5, 3)); // 8

// Implementing Interfaces
interface Flyable {
  fly(): void;
}

interface Swimmable {
  swim(): void;
}

class DuckClass implements Flyable, Swimmable {
  fly(): void {
    console.log("Flying...");
  }

  swim(): void {
    console.log("Swimming...");
  }
}

export { Person, BankAccount, Temperature, DogInherit, MathHelper };