Inheritance allows a class to reuse, extend, and specialise the behaviour of another class. The child class (subclass) inherits all public and protected members of the parent class (superclass).
extends to inherit from a parent class.parent::methodName().<?php
class Animal
{
public function __construct(
protected string $name,
protected int $age
) {}
public function speak(): string
{
return "{$this->name} makes a sound.";
}
public function describe(): string
{
return "{$this->name} is {$this->age} years old.";
}
}
class Dog extends Animal
{
public function __construct(
string $name,
int $age,
private string $breed
) {
parent::__construct($name, $age); // call parent constructor
}
// Override speak()
public function speak(): string
{
return "{$this->name} barks: Woof!";
}
// Extend describe()
public function describe(): string
{
return parent::describe() . " Breed: {$this->breed}.";
}
}
class Cat extends Animal
{
public function speak(): string
{
return "{$this->name} meows: Meow!";
}
}
$dog = new Dog('Rex', 3, 'Labrador');
$cat = new Cat('Luna', 2);
echo $dog->speak(); // Rex barks: Woof!
echo $dog->describe(); // Rex is 3 years old. Breed: Labrador.
echo $cat->speak(); // Luna meows: Meow!
// instanceof checks
echo ($dog instanceof Animal) ? 'yes' : 'no'; // yes
echo ($dog instanceof Dog) ? 'yes' : 'no'; // yes
echo ($dog instanceof Cat) ? 'yes' : 'no'; // no
Tip: Favour composition over inheritance for code reuse. Deep inheritance hierarchies become brittle and hard to reason about. Use inheritance when there is a true "is-a" relationship; inject collaborator objects for "has-a" or "uses-a" relationships.