PHP OOP Interfaces

PHP OOP Interfaces

In PHP OOP Interfaces is like a pure blueprint.
It only contains method declarations, not method bodies.

A class that implements an interface must define all its methods.

What Interfaces Do?

Force a class to follow a structure
Define rules
Allow multiple inheritance (a class can implement MANY interfaces)
Improve code architecture and flexibility

Basic Interface Example

Interface with Multiple Methods

A Class Can Implement Multiple Interfaces

PHP does not support multiple class inheritance,
but supports multiple interface inheritance.

Interface Methods Are Always Public

If you write:

In the implementing class, this is wrong:

Correct:

Interface Constants

Interfaces can contain constants:

Use it like:

Interface Extending Another Interface

Practical Example – Payment Gateway

interface PaymentGateway {
public function pay($amount);
}

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

class Paypal implements PaymentGateway {
public function pay($amount) {
echo "Paid $amount via Paypal";
}
}

$p = new Paypal();
$p->pay(500);

interface PaymentGateway {

public function pay($amount);

}

class Paytm implements PaymentGateway {

public function pay($amount) {

echo "Paid $amount via Paytm";

}

class Paypal implements PaymentGateway {

public function pay($amount) {

echo "Paid $amount via Paypal";

}

$p = new Paypal();

$p->pay(500);

Interface vs Abstract Class (Easy Table)

Feature	Interface	Abstract Class
Methods	Only abstract (PHP 7), allowed body in PHP 8	Abstract + Normal
Variables	Only constants	Properties allowed
Constructor	No	Yes
Multiple inheritance	Yes	No
Use case	Define rules	Base class with partial implementation

Summary (Easy to Remember)

Concept	Meaning
Interface	Blueprint with method declarations
implements	A class follows the rules of interface
Must override	All methods must be defined
Multiple inheritance	Class can implement many interfaces

PHP OOP Interfaces