Inheritance in php

<?php
class Animal {
    public $name;

    public function __construct($name) {
        $this->name = $name;
    }

    public function speak() {
        echo "{$this->name} makes a sound.";
    }
}

class Dog extends Animal {
    public function speak() {
        echo "{$this->name} barks!";
    }
}

$dog = new Dog("Rex");
$dog->speak(); // Rex barks!
?>

<?php
class Vehicle {
    public $brand;
    public $speed;

    public function __construct($brand, $speed) {
        $this->brand = $brand;
        $this->speed = $speed;
    }

    public function describe() {
        echo "{$this->brand} runs at {$this->speed} km/h.";
    }
}

class Car extends Vehicle {
    public $doors;

    public function __construct($brand, $speed, $doors) {
        parent::__construct($brand, $speed);
        $this->doors = $doors;
    }

    public function describe() {
        parent::describe();
        echo " It has {$this->doors} doors.";
    }
}

$car = new Car("Honda", 180, 4);
$car->describe();
// Honda runs at 180 km/h. It has 4 doors.
?>

<?php
class Shape {
    public $color;

    public function __construct($color) {
        $this->color = $color;
    }

    public function info() {
        echo "Color: {$this->color}";
    }
}

class Circle extends Shape {
    public $radius;

    public function __construct($color, $radius) {
        parent::__construct($color); // call parent constructor
        $this->radius = $radius;
    }

    public function info() {
        parent::info();
        echo ", Radius: {$this->radius}";
    }
}

$c = new Circle("red", 5);
$c->info(); // Color: red, Radius: 5
?>

<?php
class Bird {
    public function move() {
        echo "Birds fly.";
    }
}

class Penguin extends Bird {
    public function move() {
        echo "Penguins swim instead.";
    }
}

$p = new Penguin();
$p->move(); // Penguins swim instead.
?>

<?php
abstract class Shape {
    abstract public function area(): float;

    public function describe() {
        echo "This shape has area: " . $this->area();
    }
}

class Rectangle extends Shape {
    public function __construct(
        private float $width,
        private float $height
    ) {}

    public function area(): float {
        return $this->width * $this->height;
    }
}

$rect = new Rectangle(5.0, 3.0);
$rect->describe(); // This shape has area: 15
?>

<?php
class Base {
    final public function lock() {
        echo "Cannot override this.";
    }
}

// class Child extends Base { } // Error if you try to override lock()
?>

<?php
final class Singleton {
    // This class cannot be extended
}
?>

<?php
class A {
    public function hello() { echo "Hello from A"; }
}

class B extends A {
    public function world() { echo "Hello from B"; }
}

class C extends B {
    public function greet() {
        $this->hello(); // inherited from A
        $this->world(); // inherited from B
    }
}

$obj = new C();
$obj->greet();
?>