PHP OOP Abstract Classes

PHP OOP Abstract Classes

An abstract class is a class that cannot be instantiate (you cannot create objects from it).
It is used as a base/blueprint for other classes.

Key Points About Abstract Classes

You cannot create an object of an abstract class
Abstract class may have abstract methods (no body)
Child class must override abstract methods
Can have normal methods also
Supports properties & constructors
Supports protected & private members
Supports inheritance

Basic Abstract Class Example

You cannot do:

Child Class Must Define Abstract Method

Abstract Class with Normal Method

abstract class Vehicle {

public function start() {
echo "Starting engine...<br>";
}

abstract public function wheels();
}

class Car extends Vehicle {
public function wheels() {
echo "Car has 4 wheels";
}
}

$c = new Car();
$c->start();
$c->wheels();

abstract class Vehicle {

public function start() {

echo "Starting engine...<br>";

}

abstract public function wheels();

}

class Car extends Vehicle {

public function wheels() {

echo "Car has 4 wheels";

}

$c = new Car();

$c->start();

$c->wheels();

Abstract Class with Constructor

abstract class Person {
public $name;

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

abstract public function role();
}

class Student extends Person {
public function role() {
return "Student: " . $this->name;
}
}

$st = new Student("Rahul");
echo $st->role();

abstract class Person {

public $name;

public function __construct($name) {

$this->name = $name;

}

abstract public function role();

}

class Student extends Person {

public function role() {

return "Student: " . $this->name;

}

$st = new Student("Rahul");

echo $st->role();

abstract class Person {
public $name;

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

abstract public function role();
}

class Student extends Person {
public function role() {
return "Student: " . $this->name;
}
}

$st = new Student("Rahul");
echo $st->role();

abstract class Person {

public $name;

public function __construct($name) {

$this->name = $name;

}

abstract public function role();

}

class Student extends Person {

public function role() {

return "Student: " . $this->name;

}

$st = new Student("Rahul");

echo $st->role();

Multiple Abstract Methods

Why Use Abstract Classes?

Forces child classes to follow rules
Ensures structure/pattern
Useful when many classes share common behavior
Helpful in large applications
Used widely in frameworks like Laravel

Example: Laravel controller

All controllers extend it.

Abstract Class vs Interface (Important)

Feature	Abstract Class	Interface
Methods	Both normal + abstract	Only abstract (PHP 7), can have default in PHP 8
Constructor	Yes	No
Properties	Yes	(public only)
Multiple inheritance	No	Implement multiple interfaces
Use case	When base class is needed	When only rules are needed

Practical Example

Making a universal payment system:

abstract class Payment {
abstract public function pay($amount);
}

class Paytm extends Payment {
public function pay($amount) {
echo "Paid $amount via Paytm";
}
}

class Paypal extends Payment {
public function pay($amount) {
echo "Paid $amount via PayPal";
}
}

$p = new Paytm();
$p->pay(100);

abstract class Payment {

abstract public function pay($amount);

}

class Paytm extends Payment {

public function pay($amount) {

echo "Paid $amount via Paytm";

}

class Paypal extends Payment {

public function pay($amount) {

echo "Paid $amount via PayPal";

}

$p = new Paytm();

$p->pay(100);

Summary (Easy to Remember)

Concept	Meaning
abstract class	Cannot make object, used as base
abstract method	Must be implemented by child
extends	Child inherits abstract class
Purpose	Enforce structure in child classes

PHP OOP Abstract Classes