Simple OOP with Interface, Inheritance and static properties.

Php-OOP-experiments.php

<?php 
interface IAnimal {
	public function setSound($sound);
	public function getSound();
}
class Animal implements IAnimal {
	protected static $sound;
	protected $type;
	protected $name;

	public function __construct()
	{
		static::$sound = 'Default sound';
	}
	public function setSound($sound)
	{
		self::$sound = $sound;	
	}
	public function getSound()
	{
		return self::$sound;
	}
	public static function mySound()
	{
		return static::$sound;
	}
}

class Dog extends Animal {
	public function __construct()
	{
		$this->name = 'Doggie';
	}
}
class Cat extends Animal {
	public function __construct()
	{
		$this->name = 'Mingming';
	}
}

$cat = new Cat();
$cat->setSound('Meow meow');
echo $cat->getSound();

$dog = new Dog();
$dog->setSound('Aw aw aw');
echo $dog->getSound();

echo ' -retain- ' . $dog::mySound();

echo '<pre>', var_dump($dog);
echo '<pre>', var_dump($cat);