PHP Inheritance

PHP inheritance is a fundamental concept in object-oriented programming (OOP) that allows a class to inherit properties and methods from another class. The class that inherits is called the child or subclass, while the class being inherited from is called the parent or superclass.

Here’s an explanation with examples to illustrate PHP inheritance:

Basic Example

Parent Class

<?php
class Animal {
    public $name;

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

    public function makeSound() {
        return "Some generic sound";
    }
}
?>

Child Class

<?php
class Dog extends Animal {
    public function makeSound() {
        return "Bark";
    }
}

$dog = new Dog("Buddy");
echo $dog->name; // Outputs: Buddy
echo $dog->makeSound(); // Outputs: Bark
?>

In this example:

• The Animal class is the parent class with a property $name and a method makeSound().
• The Dog class is the child class that extends Animal. It inherits the $name property and the makeSound() method, but it overrides the makeSound() method to return "Bark".
• When we create an instance of Dog, we can access the inherited $name property and the overridden makeSound() method.

Using parent Keyword

The parent keyword allows the child class to call methods and access properties of its parent class.

Modified Example

<?php
class Animal {
    public $name;

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

    public function makeSound() {
        return "Some generic sound";
    }
}

class Dog extends Animal {
    public function makeSound() {
        return parent::makeSound() . " and Bark";
    }
}

$dog = new Dog("Buddy");
echo $dog->makeSound(); // Outputs: Some generic sound and Bark
?>

In this modified example:

• The Dog class still extends Animal.
• The makeSound() method in the Dog class calls the parent’s makeSound() method using parent::makeSound() and appends " and Bark" to the result.

Access Modifiers

Access modifiers determine the visibility of properties and methods in a class. PHP supports public, protected, and private.

Example with Access Modifiers

<?php
class Animal {
    public $name;
    protected $type;

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

    protected function getType() {
        return $this->type;
    }

    public function makeSound() {
        return "Some generic sound";
    }
}

class Dog extends Animal {
    public function __construct($name) {
        parent::__construct($name, "Dog");
    }

    public function getTypeInfo() {
        return $this->getType(); // Accessing protected method
    }

    public function makeSound() {
        return "Bark";
    }
}

$dog = new Dog("Buddy");
echo $dog->name; // Outputs: Buddy
echo $dog->getTypeInfo(); // Outputs: Dog
echo $dog->makeSound(); // Outputs: Bark
?>

In this example:

• The Animal class has a protected property $type and a protected method getType().
• The Dog class extends Animal and can access the protected members of Animal using its own public method getTypeInfo().

Final Classes and Methods

The final keyword prevents classes or methods from being extended or overridden.

Example with final

<?php
class Animal {
    public $name;

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

    final public function makeSound() {
        return "Some generic sound";
    }
}

class Dog extends Animal {
    // This will cause an error
    // public function makeSound() {
    //     return "Bark";
    // }
}

$dog = new Dog("Buddy");
echo $dog->makeSound(); // Outputs: Some generic sound
?>

In this example:

• The makeSound() method in the Animal class is declared as final, meaning it cannot be overridden in any subclass.

These examples illustrate the basics of inheritance in PHP, including how to use the parent keyword, access modifiers, and the final keyword to control inheritance behavior.