Inheritance in PHP

Welcome to the next lesson! In this lesson, you’ll learn about inheritance, a core concept in Object-Oriented Programming (OOP) that allows you to extend the functionality of a class. Let’s get started!

What Is Inheritance?

Inheritance is a mechanism in OOP that allows one class (child class) to inherit properties and methods from another class (parent class). This promotes code reuse and hierarchy in programming.

Example: A Car class can serve as a parent for Sedan and SUV classes.

Defining Inheritance

Use the extends keyword to create a child class that inherits from a parent class. Example:

Tip: Use inheritance to avoid duplicating code.

<h2>Defining Inheritance</h2>
<p>Use the <code>extends</code> keyword to create a child class that inherits from a parent class. Example:</p>

Overriding Methods

Child classes can override methods from the parent class to provide specific functionality. Example:

<?php
  class Vehicle {
    public function drive() {
      echo "Driving a generic vehicle.";
    }
  }

  class Car extends Vehicle {
    public function drive() {
      echo "Driving a car.";
    }
  }

  $car = new Car();
  $car->drive(); // Outputs: Driving a car.
?>

The parent Keyword

Use the parent keyword to call a parent class method inside an overridden method. Example:

<?php
  class Vehicle {
    public function start() {
      echo "Starting the vehicle.";
    }
  }

  class Car extends Vehicle {
    public function start() {
      parent::start();
      echo " Starting the car engine.";
    }
  }

  $car = new Car();
  $car->start(); // Outputs: Starting the vehicle. Starting the car engine.
?>

Benefits of Inheritance

Inheritance offers the following advantages:

• Promotes code reuse.
• Establishes a clear class hierarchy.
• Enables polymorphism by allowing child classes to override methods.

Protected Members

Inheritance also works with protected members. Protected properties and methods are accessible to child classes but not outside the class hierarchy. Example:

Key Point: Use protected to share members between parent and child classes securely.

<?php
  class Vehicle {
    protected $fuel;

    public function setFuel($fuel) {
      $this->fuel = $fuel;
    }
  }

  class Car extends Vehicle {
    public function getFuel() {
      return $this->fuel;
    }
  }

  $car = new Car();
  $car->setFuel("Gasoline");
  echo "Fuel: " . $car->getFuel(); // Outputs: Fuel: Gasoline
?>

Abstract Classes

An abstract class provides a base structure for child classes but cannot be instantiated itself. Example:

Key Point: Use abstract classes when you want to enforce certain methods in child classes.

<?php
  abstract class Vehicle {
    abstract public function start();
  }

  class Car extends Vehicle {
    public function start() {
      echo "Starting the car engine.";
    }
  }

  $car = new Car();
  $car->start(); // Outputs: Starting the car engine.
?>

Final Keyword

The final keyword prevents further inheritance or overriding. Example:

Tip: Use final to protect methods or classes from being extended.

<?php
  class Vehicle {
    final public function start() {
      echo "Starting the vehicle.";
    }
  }

  class Car extends Vehicle {
    // Cannot override the start method
  }
?>

Great Job!

Congratulations! You’ve learned about inheritance in PHP, including how to extend classes, override methods, and use abstract classes. In the next lesson, we’ll explore encapsulation and access modifiers. Let’s keep coding!