What are Abstract classes and methods in PHP OOP?

What are Abstract classes?

If you want to write a class only to inherit the class and not to create the objects of the class, then abstract classes do that job for you.

• You cannot create the objects or instances of an abstract class.
• Properties and methods of abstract classes can only be accessed through child classes.

How to create Abstract classes in PHP?

PHP OOP has a keyword called abstract which is used to turn a class into an abstract class.

You have to write this abstract keyword before the class keyword like the following syntax –

abstract class ClassName{
    // Properties and Methods
}

Example of Abstract Class

<?php
abstract class MyAbsClass{
    private $name = 'John';
    public function sayHello(){
        echo "Hello ".$this->name;
    }
}

class MyClass extends MyAbsClass{
    function __construct()
    {
        $this->sayHello();
    }
}

$obj = new MyClass();
/**
    ❌ You cannot do this
    $obj = new MyAbsClass();
 */

Hello John

---

Abstract methods in PHP OOP

You can also create abstract methods with the help of the abstract keyword.

Few rules for creating abstract methods

• You can create abstract methods only inside the abstract classes.
• You cannot describe the body of the the abstract methods inside the abstract class. You are only allowed to declare the the abstract method inside the abstract class.
• You must have to describe the body of the abstract methods inside the child classes.

<?php
abstract class MyAbsClass{
    // Declaring the SayHello Function
    abstract function sayHello($a);
}

class MyClass extends MyAbsClass{
    // Describing the body of the SayHello Function
    function sayHello($name){
        echo "Hello $name";
    }
}

$obj = new MyClass();
$obj->sayHello('Mark');

Important notes for abstract methods

1. Abstract methods cannot be declared private. It could be public or protected.

// ❌ Wrong - you cannot do this
abstract private function sayHello($a);

// ✔️ Right Way
abstract public function sayHello($a);
// OR - It is also right ✔️
abstract protected function sayHello($a);

2. The access modifier of an abstract method must be the same or weaker in the child class.

Abstract Class	Child Class
public	public
protected	protected or public

abstract protected function sayHello($a);

// ❌ Wrong
private function sayHello($name){
    echo "Hello $name";
}

// ✔️ Right Way
public function sayHello($name){
    echo "Hello $name";
}

// OR - It is also right ✔️
protected function sayHello($name){
    echo "Hello $name";
}