PHP Inheritance

Inheritance is one of the most powerful features of Object-Oriented Programming. it allows a class to **inherit** properties and methods from another class. This promotes code reusability and helps you create a hierarchical structure in your applications.

Parent and Child Classes

In inheritance, we deal with two types of classes:

• Parent Class (Base Class): The class whose properties and methods are being inherited.
• Child Class (Derived Class): The class that inherits from the parent class.

The extends Keyword

You use the extends keyword to create a child class that inherits from a parent class.

<?php
    class Fruit {
        public $name;
        public $color;

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

        public function intro() {
            echo "The fruit is {$this->name} and the color is {$this->color}.";
        }
    }

    // Strawberry inherits from Fruit
    class Strawberry extends Fruit {
        public function message() {
            echo "Am I a fruit or a berry? ";
        }
    }

    $strawberry = new Strawberry("Strawberry", "red");
    $strawberry->message(); // Child method
    $strawberry->intro();   // Inherited parent method
?>

Overriding Inherited Methods

Inherited methods can be **overridden** by redefining them in the child class. This is useful when a child class needs to perform the same action but in a different way.

<?php
    class Fruit {
        public function intro() {
            echo "I am a fruit.";
        }
    }

    class Strawberry extends Fruit {
        // Overriding the parent method
        public function intro() {
            echo "I am a strawberry, specifically.";
        }
    }

    $strawberry = new Strawberry();
    $strawberry->intro(); // Outputs: I am a strawberry, specifically.
?>

The final Keyword

The final keyword can be used to prevent class inheritance or to prevent method overriding. If a class is marked as final, it cannot be extended. If a method is marked as final, it cannot be overridden by child classes.

<?php
    final class Fruit {
        // This class cannot be inherited
    }

    class Strawberry extends Fruit {
        // This will cause a Fatal Error!
    }
?>

Why Use Inheritance?

• Code Reusability: Write common code in the parent class and reuse it across multiple child classes.
• Scalability: Easily add new child classes without modifying existing parent class code.
• Organization: Group related classes into a logical hierarchy (e.g., Vehicle -> Car -> ElectricCar).
• Consistency: Ensures that all child classes have a common set of features defined by the parent.

Summary

• Inheritance allows a child class to use properties and methods of a parent class.
• Use extends to create a child class.
• Child classes can override parent methods to change their behavior.
• The final keyword stops a class from being inherited or a method from being overridden.
• PHP supports single inheritance only.