Inheritance in PHP

Welcome back! Now that you have a solid understanding of classes and objects in PHP, it's time to build on that knowledge by exploring inheritance . Consider it a natural progression in our journey into object-oriented programming (OOP). Inheritance allows you to create a new class based on an existing class. By using inheritance, you can reuse code, add new features, and make your programs easier to manage and understand. Let's dive in and see what it's all about.

What You'll Learn

In this lesson, you'll understand how to use inheritance in PHP. We'll cover: What Inheritance Is How to Implement Inheritance in PHP Why Inheritance Is Beneficial

What Inheritance Is

Inheritance is a way to establish a relationship between a new class (child class) and an existing class (parent class). The child class inherits properties and behaviors (methods) from the parent class. Here’s a simple example: <?php // Define the base class Person with name and age attributes class Person { // Declare properties private $name; private $age; // Constructor to initialize name and age public function __construct($name, $age) { $this->name = $name; $this->age = $age; } // Display method to show name and age public function display() { echo "Name: " . $this->name . ", Age: " . $this->age . "\n"; } // Greet method to display a greeting message public function greet() { echo "Hello, there!\n"; } } // Define the derived class Student, inheriting from Person class Student extends Person { // Declare property for major private $major; // Constructor to initialize name, age of the base class, and the major of the student public function __construct($name, $age, $major) { // Call parent constructor to initialize base attributes parent::__construct($name, $age); $this->major = $major; } // Display method to show name, age using the base class display method, and major of the student public function display() { $this->greet(); parent::display(); echo "Major: " . $this->major . "\n"; } } // Create a Student object and display its details $student = new Student("Bob", 25, "Computer Science"); $student->display(); ?> In this snippet, the Student class inherits from the Person class. It reuses the name and age attributes and methods from the Person class and adds a new attribute major and a new display method to show the student's major. When you declare a child class, you specify the parent class it inherits from by using the extends keyword. The child class can then extend or override the functionality of the parent class. In our example: The Person class is the parent class. The Student class is the child class, inheriting name and age from the Person class. The Student class also adds a new member, major, and overrides the display method to include information about the major. Notice how Student::display() calls parent::display() to reuse the parent class functionality before adding its details. The greet method is also called from the display method to show how the child class can access parent class methods.

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PHP

<?php

// Define the base class Person with name and age attributes
class Person {
    // Declare properties
    private $name;
    private $age;

    // Constructor to initialize name and age
    public function __construct($name, $age) {
        $this->name = $name;
        $this->age = $age;
    }

    // Display method to show name and age
    public function display() {
        echo "Name: " . $this->name . ", Age: " . $this->age . "\n";
    }

    // Greet method to display a greeting message
    public function greet() {
        echo "Hello, there!\n";
    }
}

// Define the derived class Student, inheriting from Person
class Student extends Person {
    // Declare property for major
    private $major;

    // Constructor to initialize name, age of the base class, and the major of the student
    public function __construct($name, $age, $major) {
        // Call parent constructor to initialize base attributes
        parent::__construct($name, $age);
        $this->major = $major;
    }

    // Display method to show name, age using the base class display method, and major of the student
    public function display() {
        $this->greet();
        parent::display();
        echo "Major: " . $this->major . "\n";
    }
}

// Create a Student object and display its details
$student = new Student("Bob", 25, "Computer Science");
$student->display();

?>

<?php

// Define the base class Person with name and age attributes
class Person {
    // Declare properties
    private $name;
    private $age;

    // Constructor to initialize name and age
    public function __construct($name, $age) {
        $this->name = $name;
        $this->age = $age;
    }

    // Display method to show name and age
    public function display() {
        echo "Name: " . $this->name . ", Age: " . $this->age . "\n";
    }

    // Greet method to display a greeting message
    public function greet() {
        echo "Hello, there!\n";
    }
}

// Define the derived class Student, inheriting from Person
class Student extends Person {
    // Declare property for major
    private $major;

    // Constructor to initialize name, age of the base class, and the major of the student
    public function __construct($name, $age, $major) {
        // Call parent constructor to initialize base attributes
        parent::__construct($name, $age);
        $this->major = $major;
    }

    // Display method to show name, age using the base class display method, and major of the student
    public function display() {
        $this->greet();
        parent::display();
        echo "Major: " . $this->major . "\n";
    }
}

// Create a Student object and display its details
$student = new Student("Bob", 25, "Computer Science");
$student->display();

?>

PHP

<?php

// Define the base class Animal with a protected property and method
class Animal {
    // Declare a protected property
    protected $name;

    // Constructor to initialize name
    public function __construct($name) {
        $this->name = $name;
    }

    // Protected method to describe the animal
    protected function describe() {
        echo "This is an animal named " . $this->name . ".\n";
    }
}

// Define the derived class Dog, inheriting from Animal
class Dog extends Animal {
    // Method to show details about the dog
    public function showDetails() {
        // Access the protected property and method from the parent class
        echo "Dog's Name: " . $this->name . "\n";
        $this->describe();
    }
}

// Create a Dog object and display its details
$dog = new Dog("Buddy");
$dog->showDetails();

?>

<?php

// Define the base class Animal with a protected property and method
class Animal {
    // Declare a protected property
    protected $name;

    // Constructor to initialize name
    public function __construct($name) {
        $this->name = $name;
    }

    // Protected method to describe the animal
    protected function describe() {
        echo "This is an animal named " . $this->name . ".\n";
    }
}

// Define the derived class Dog, inheriting from Animal
class Dog extends Animal {
    // Method to show details about the dog
    public function showDetails() {
        // Access the protected property and method from the parent class
        echo "Dog's Name: " . $this->name . "\n";
        $this->describe();
    }
}

// Create a Dog object and display its details
$dog = new Dog("Buddy");
$dog->showDetails();

?>

PHP

<?php

// Define the base class Person with name and age attributes
class Person {
    // Declare properties
    private $name;
    private $age;

    // Constructor to initialize name and age
    public function __construct($name, $age) {
        $this->name = $name;
        $this->age = $age;
    }

    // Display method to show name and age
    public function display() {
        echo "Name: " . $this->name . ", Age: " . $this->age . "\n";
    }

    // Greet method to display a greeting message
    public function greet() {
        echo "Hello, there!\n";
    }
}

// Define the derived class Student, inheriting from Person
class Student extends Person {
    // Declare property for major
    private $major;

    // Constructor to initialize name, age of the base class, and the major of the student
    public function __construct($name, $age, $major) {
        // Call parent constructor to initialize base attributes
        parent::__construct($name, $age);
        $this->major = $major;
    }

    // Display method to show name, age using the base class display method, and major of the student
    public function display() {
        $this->greet();
        parent::display();
        echo "Major: " . $this->major . "\n";
    }
}

// Create a Student object and display its details
$student = new Student("Bob", 25, "Computer Science");
$student->display();

?>

PHP

<?php

// Define the base class Animal with a protected property and method
class Animal {
    // Declare a protected property
    protected $name;

    // Constructor to initialize name
    public function __construct($name) {
        $this->name = $name;
    }

    // Protected method to describe the animal
    protected function describe() {
        echo "This is an animal named " . $this->name . ".\n";
    }
}

// Define the derived class Dog, inheriting from Animal
class Dog extends Animal {
    // Method to show details about the dog
    public function showDetails() {
        // Access the protected property and method from the parent class
        echo "Dog's Name: " . $this->name . "\n";
        $this->describe();
    }
}

// Create a Dog object and display its details
$dog = new Dog("Buddy");
$dog->showDetails();

?>

Inheritance in PHP

What You'll Learn

What Inheritance Is

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Understanding the Protected Modifier

Why It Matters