In PHP Object-Oriented Programming (OOP), parent and child classes are fundamental concepts that allow for inheritance, enabling you to create a new class based on an existing class. Here's an explanation of each, along with examples:

Parent Class

A parent class (also known as a base class or superclass) is a class that provides common properties and methods that can be shared with other classes. It serves as a foundation for child classes.

Child Class

A child class (also known as a derived class or subclass) is a class that inherits properties and methods from a parent class. The child class can also have its own properties and methods, as well as override methods from the parent class if needed.

Inheritance

Inheritance allows a child class to use the properties and methods of the parent class, promoting code reuse and a hierarchical class structure.

Example

Here’s an example to illustrate parent and child classes in PHP OOP:

<?php
// Parent Class
class Animal {
    public $name;

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

    public function speak() {
        return "The animal makes a sound.";
    }
}

// Child Class
class Dog extends Animal {
    public function speak() {
        return "The dog barks.";
    }
}

// Another Child Class
class Cat extends Animal {
    public function speak() {
        return "The cat meows.";
    }
}

// Creating Objects
$dog = new Dog("Buddy");
$cat = new Cat("Whiskers");

echo $dog->name . ": " . $dog->speak(); // Outputs: Buddy: The dog barks.
echo "\n";
echo $cat->name . ": " . $cat->speak(); // Outputs: Whiskers: The cat meows.
?>

Breakdown of the Example

1. Parent Class (Animal):

   • The Animal class is defined as the parent class.
   • It has a property called $name and a method called speak().
   • The speak() method provides a generic message for any animal.

2. Child Classes (Dog and Cat):

   • The Dog and Cat classes are defined as child classes that extend the Animal class.
   • Both classes inherit the $name property and the constructor from the Animal class.
   • Each child class overrides the speak() method to provide a specific message for that animal type.

3. Creating Objects:

   • Instances of the Dog and Cat classes are created, and their respective speak() methods are called.
   • Each object can access the properties and methods of the parent class while also providing its specific implementation of the speak() method.

Benefits of Using Parent and Child Classes

• Code Reusability: Common functionality is centralized in the parent class, reducing code duplication.
• Maintainability: Changes made in the parent class automatically apply to child classes, making maintenance easier.
• Polymorphism: Child classes can override methods, allowing for dynamic method resolution based on the object type.

Summary

Parent and child classes in PHP OOP enable you to create a clear hierarchy of classes, promoting code reuse and better organization of your codebase. Through inheritance, child classes can inherit properties and methods from parent classes, making it easier to manage related objects and behaviors.