PHP Constructors & Destructors

<?php
class Car {
    public $model;
    
    // Constructor
    public function __construct() {
        $this->model = "Unknown";
        echo "A new car object has been created.\n";
    }
}

// Create object
$myCar = new Car();
echo "Model: " . $myCar->model . "\n";
?>

<?php
class Book {
    public $title;
    public $author;
    
    public function __construct($title, $author) {
        $this->title = $title;
        $this->author = $author;
        echo "Book '{$this->title}' created.\n";
    }
}

$myBook = new Book("PHP for Beginners", "John Doe");
echo "Title: {$myBook->title}, Author: {$myBook->author}\n";
?>

<?php
class Product {
    // Properties are declared and assigned directly in constructor parameters
    public function __construct(
        public string $name,
        public float $price,
        public int $quantity = 1
    ) {
        echo "Product {$this->name} initialized.\n";
    }
}

$laptop = new Product("Laptop", 999.99, 2);
echo "{$laptop->name}, Price: \${$laptop->price}, Qty: {$laptop->quantity}\n";
?>

<?php
class FileHandler {
    private $file;
    
    public function __construct($filename) {
        $this->file = fopen($filename, 'w');
        echo "File {$filename} opened for writing.\n";
    }
    
    public function write($content) {
        fwrite($this->file, $content);
    }
    
    public function __destruct() {
        if ($this->file) {
            fclose($this->file);
            echo "File closed and resources released.\n";
        }
    }
}

$handler = new FileHandler("test.txt");
$handler->write("Hello, PHP!");
// Destructor is called automatically when script ends or object is unset
?>

<?php
class Animal {
    protected $name;
    
    public function __construct($name) {
        $this->name = $name;
        echo "Animal {$this->name} created.\n";
    }
    
    public function __destruct() {
        echo "Animal {$this->name} destroyed.\n";
    }
}

class Dog extends Animal {
    private $breed;
    
    public function __construct($name, $breed) {
        parent::__construct($name); // Call parent constructor
        $this->breed = $breed;
        echo "Dog of breed {$this->breed} created.\n";
    }
    
    public function __destruct() {
        echo "Dog {$this->name} destroyed.\n";
        parent::__destruct(); // Call parent destructor
    }
}

$myDog = new Dog("Buddy", "Golden Retriever");
// Destructor will be called at the end of script
?>

<?php
class Database {
    private $connection;
    
    public function __construct($host, $user, $pass, $db) {
        $this->connection = new mysqli($host, $user, $pass, $db);
        if ($this->connection->connect_error) {
            die("Connection failed: " . $this->connection->connect_error);
        }
        echo "Connected to database successfully.\n";
    }
    
    public function query($sql) {
        return $this->connection->query($sql);
    }
    
    public function __destruct() {
        if ($this->connection) {
            $this->connection->close();
            echo "Database connection closed.\n";
        }
    }
}

// Usage
$db = new Database("localhost", "username", "password", "testdb");
$result = $db->query("SELECT * FROM users");
// Process results...
// Destructor will close connection automatically
?>

<?php
class ShoppingCart {
    private $items = [];
    private static $cartCount = 0;
    
    public function __construct() {
        self::$cartCount++;
        echo "Shopping cart created. Total carts: " . self::$cartCount . "\n";
    }
    
    public function addItem($item) {
        $this->items[] = $item;
        echo "Added {$item} to cart.\n";
    }
    
    public function __destruct() {
        self::$cartCount--;
        echo "Cart destroyed. Items removed: " . count($this->items) . "\n";
        echo "Remaining carts: " . self::$cartCount . "\n";
    }
}

$cart1 = new ShoppingCart();
$cart1->addItem("Laptop");
$cart1->addItem("Mouse");

$cart2 = new ShoppingCart();
$cart2->addItem("Keyboard");

unset($cart1); // Explicitly destroy first cart
?>