The Ultimate Guide to Interfaces in PHP: Definition, Implementation, and Best Practices for 2025

An interface in PHP defines a contract for classes, specifying methods they must implement. Understanding the role of an interface in PHP is crucial for designing modular, maintainable code. 

Read on to learn more about this essential concept! 

What is an Interface in PHP and Its Role in OOPs?

An interface in PHP acts as a blueprint for multiple classes, simplifying code structure and ensuring consistency. While, in object-oriented programming, an interface is a contract that defines the methods a class must implement, without specifying how these methods should be executed.

Interfaces are invaluable in achieving abstraction, as they define what methods a class should have without specifying how they are executed. 

Here’s how interfaces in PHP simplify and streamline your code.

• Provides Consistent Structure: Interfaces ensure that multiple classes follow the same method structure, making code easier to manage and extend.
• Promotes Reusability: Once a method is defined in an interface, it can be reused across different classes without rewriting the same code.
• Enhances Flexibility: You can implement the same interface in different ways, depending on your requirements, making your system more adaptable.

Interfaces in PHP also contribute significantly to abstraction and loose coupling. This is especially beneficial for creating scalable and maintainable applications. Here are key ways interfaces in PHP simplify and streamline your code.

• Abstraction: Interfaces separate method declarations from their implementation, allowing for a high level of abstraction in your application.
• Loose Coupling: By using interfaces, components can interact without knowing the internal details of each other, fostering independence and reducing complexity.

Here are examples of interfaces across different programming languages.

• Java: Interfaces in Java define methods without implementation. This allows classes to implement multiple Java interfaces, aiding in building flexible systems.
• C#: C# uses interfaces to define method signatures. Different classes implement these methods, ensuring consistency across applications.
• Python: While Python doesn’t have a formal interface structure, similar functionality is achieved through abstract base classes, which define a contract for subclasses.

By understanding the role of interfaces in OOPs, you gain insight into how they contribute to designing efficient and maintainable code structures.

Also Read: PHP Tutorial: Learn from Basics

Now that you understand what an interface is in PHP and its significance in OOP, let’s delve deeper into the key features that make interfaces so powerful.

Key Features of Interfaces in PHP

Interfaces in PHP have distinct characteristics that differentiate them from other elements of object-oriented programming (OOP). Understanding these features is crucial for anyone looking to harness the full potential of interfaces in PHP. 

Here are the key features of interfaces in PHP.

• No Method Implementation, Only Declarations: An interface in PHP does not provide the implementation of methods, only the method declarations. The class implementing the interface is responsible for defining the method logic.
• Methods Must Be Public: All methods declared in an interface are implicitly public. This ensures that the methods are accessible to any class that implements the interface.
• Classes Must Define All Interface Methods: When a class implements an interface, it must define all the methods declared by that interface. Failure to do so will result in a fatal error.
• Interfaces Cannot Contain Variables: Unlike classes, interfaces cannot contain properties or types of variables. They can only declare methods, leaving the implementation details to the implementing classes.
• One Class Can Implement Multiple Interfaces: A key feature of interfaces in PHP is that a class can implement multiple interfaces, allowing it to inherit method declarations from more than one source. This increases flexibility and promotes cleaner code.

Now that you’ve explored the key features of interfaces in PHP, it’s time to dive deeper and understand the syntax that brings these concepts to life.

Understanding the Syntax of Interfaces in PHP

To effectively work with interfaces in PHP, it is essential to understand the syntax used to define and implement them. The interface keyword is used to declare an interface, and the implements keyword is used when a class adopts the interface's method signatures. 

The combination of these two keywords allows you to maintain a clear contract between classes, ensuring consistency in method definitions.

Here’s a breakdown of the syntax for defining and implementing interfaces in PHP.

• Defining an Interface: The interface keyword is used to define an interface. Inside the interface, you declare method signatures without providing the actual implementation.
• Implementing an Interface: The implements keyword allows a class to implement the methods defined in the interface. The class must then provide the actual implementation of these methods.

Code Example: Defining and Implementing an Interface in PHP

This example demonstrates how to define an interface and implement it in a class.

Code Snippet:

// Define an interface called 'Car'
interface Car {
    public function startEngine();  // Method declaration
    public function stopEngine();   // Method declaration
}

// Implement the 'Car' interface in a class called 'Tesla'
class Tesla implements Car {
    // Implement the startEngine method
    public function startEngine() {
        echo "Tesla engine started.\n";
    }
    
    // Implement the stopEngine method
    public function stopEngine() {
        echo "Tesla engine stopped.\n";
    }
}

// Create an object of the Tesla class
$myTesla = new Tesla();

// Call the methods defined in the Car interface
$myTesla->startEngine();  // Output: Tesla engine started.
$myTesla->stopEngine();   // Output: Tesla engine stopped.

Output:

Tesla engine started.
Tesla engine stopped.

Explanation:

• Defining the Interface: The Car interface is defined with two methods, startEngine() and stopEngine(). These methods do not have implementations; they only declare what functions the class should implement.
• Implementing the Interface: The Tesla class implements the Car interface using the implements keyword. Inside the class, the methods startEngine() and stopEngine() are given concrete implementations.
• Creating an Object: The $myTesla object of the Tesla class is created, and the methods defined in the Car interface are called. The output demonstrates that the Tesla class has successfully implemented the interface's methods.

Also Read: Abstract Class vs Interface: The Differences and the Similarities

Now that you understand the syntax of interfaces in PHP, let’s explore some real-world examples to see how they bring structure and flexibility to your code.

Real-World Examples of Interfaces in PHP

Interfaces in PHP can be applied in various real-world scenarios, demonstrating their versatility and power in object-oriented programming (OOP). By using interfaces, you can define a clear contract for classes to follow while promoting code reusability, modularity, and polymorphism. 

The following examples show practical applications and the expected output of each to help you understand how to use interfaces in different situations.

Simple Example: Logging with Monolog

This example demonstrates how to integrate a custom logging interface with Monolog, a popular logging library.

Code Snippet:

// Define a custom Logger interface
interface CustomLogger {
    public function log($message);  // Method declaration
}

// Implement the Logger interface using Monolog
use Monolog\Logger;
use Monolog\Handler\StreamHandler;

class MonologLogger implements CustomLogger {
    private $logger;

    public function __construct() {
        $this->logger = new Logger('custom_logger');
        $this->logger->pushHandler(new StreamHandler('app.log', Logger::INFO));
    }

    public function log($message) {
        $this->logger->info($message);
        echo "Message logged: $message\n";
    }
}

// Example usage
$logger = new MonologLogger();
$logger->log("Payment successful by Rajesh.");  // Output: Message logged: Payment successful by Rajesh.

Output: Message logged: Payment successful by Rajesh.

Explanation:

1. The CustomLogger interface defines a generic contract for logging.
2. The MonologLogger class implements this interface and integrates with Monolog to log messages.
3. By using Monolog’s Logger class, messages are logged to a file and output to the console, demonstrating real-world integration.

Also Read: Serializable Interface in Java with Examples

Simple Example: Middleware System for HTTP Requests

This example demonstrates creating an interface for middleware systems to handle HTTP requests.

Code Snippet:

// Define a Middleware interface
interface Middleware {
    public function handle($request);
}

// Implement the Middleware interface for authentication
class AuthenticationMiddleware implements Middleware {
    public function handle($request) {
        if ($request['authenticated']) {
            echo "User authenticated: Welcome, Sita.\n";
        } else {
            echo "Authentication failed.\n";
        }
    }
}

// Example usage
$request = ['authenticated' => true];
$middleware = new AuthenticationMiddleware();
$middleware->handle($request);  // Output: User authenticated: Welcome, Sita.

Output: User authenticated: Welcome, Sita.

Explanation:

1. The Middleware interface ensures a consistent contract for processing HTTP requests.
2. The AuthenticationMiddleware implements the interface to handle authentication logic.
3. This approach makes it easy to add more middleware classes (e.g., logging, validation) without altering existing logic.

Also Read: Runnable Interface in Java: Implementation, Steps & Errors

Advanced Example: Plugin Architecture

This advanced example demonstrates how to use interfaces for defining contracts in a plugin architecture for a blogging platform.

Code Snippet:

// Define a Plugin interface
interface BlogPlugin {
    public function execute();
}

// Implement the Plugin interface for a comment moderation plugin
class CommentModerationPlugin implements BlogPlugin {
    public function execute() {
        echo "Comment moderation activated for posts by Priya.\n";
    }
}

// Implement the Plugin interface for a SEO optimization plugin
class SEOPlugin implements BlogPlugin {
    public function execute() {
        echo "SEO optimization activated for Priya's blog.\n";
    }
}

// Example usage
$plugins = [new CommentModerationPlugin(), new SEOPlugin()];
foreach ($plugins as $plugin) {
    $plugin->execute();
}

Output: Comment moderation activated for posts by Priya.
SEO optimization activated for Priya's blog.

Explanation:

1. The BlogPlugin interface defines the contract for plugins.
2. Each plugin implements the interface, allowing for easy addition of new plugins without altering the core platform.
3. The architecture supports modularity, enabling developers to add or remove plugins dynamically.

Also Read: What are the Advantages of Object-Oriented Programming?

Advanced Example: Middleware System with Multiple Middleware

This example demonstrates a more complex middleware system that chains multiple middleware classes to process HTTP requests.

Code Snippet:

// Define a Middleware interface
interface Middleware {
    public function handle($request, $next);
}

// Implement the Middleware interface for Authentication
class AuthenticationMiddleware implements Middleware {
    public function handle($request, $next) {
        if (!$request['authenticated']) {
            echo "Authentication failed.\n";
            return;
        }
        echo "Authentication passed for Ramesh.\n";
        $next($request);
    }
}

// Implement the Middleware interface for Logging
class LoggingMiddleware implements Middleware {
    public function handle($request, $next) {
        echo "Logging request for user: Ramesh.\n";
        $next($request);
    }
}

// Middleware chain implementation
class MiddlewareChain {
    private $middlewares = [];

    public function addMiddleware(Middleware $middleware) {
        $this->middlewares[] = $middleware;
    }

    public function handle($request) {
        $handler = array_reduce(
            array_reverse($this->middlewares),
            fn ($next, $middleware) => fn ($req) => $middleware->handle($req, $next),
            fn ($req) => null
        );
        $handler($request);
    }
}

// Example usage
$request = ['authenticated' => true];
$chain = new MiddlewareChain();
$chain->addMiddleware(new AuthenticationMiddleware());
$chain->addMiddleware(new LoggingMiddleware());
$chain->handle($request);

// Output:
// Authentication passed for Ramesh.
// Logging request for user: Ramesh.

Output: Authentication passed for Ramesh.
Logging request for user: Ramesh.

Explanation:

1. The Middleware interface ensures each middleware adheres to a common structure.
2. The AuthenticationMiddleware and LoggingMiddleware classes process the request sequentially.
3. The MiddlewareChain allows chaining middleware dynamically, making it scalable for adding new processing steps.

Now that you’ve explored real-world applications of interfaces in PHP, it’s time to learn how to create them with a clear, step-by-step approach.

How to Create an Interface in PHP: A Step-by-Step Guide

Creating an interface in PHP is a fundamental aspect of object-oriented programming (OOP). Interfaces in PHP define a contract for classes to follow. They declare method signatures without providing implementation details. 

This structure ensures that the implementing classes adhere to specific rules, promoting consistency across different components of an application. 

Here’s the process of creating and using interfaces broken down.

Step 1: Define the Interface

The first step in creating an interface in PHP is to define it using the interface keyword. The interface should declare method signatures, which must be implemented by any class that follows the contract.

To start implementing interfaces effectively, follow these key steps for defining and structuring them in PHP.

• Use the interface keyword followed by the name of the interface.
• Declare method signatures inside the interface. These methods must be public.
• No method bodies are provided in the interface—just the method declarations.

Also Read: OOPS Concept in Java Explained for Beginners

Step 2: Implement the Interface in a Class

Once an interface is defined, a class must implement it using the implements keyword. The class must then define all the methods declared in the interface.

To implement an interface in PHP effectively, follow these essential steps.

• Use the implements keyword in the class declaration.
• The class must implement all the methods declared in the interface.
• Ensure the method signatures in the class match those in the interface.

Also Read: How to Become a PHP Developer in 2025: A Complete Beginner's Guide

Step 3: Use the Interface in Application

Now that the interface is defined and implemented, it can be used in your application. Classes that implement the interface can be instantiated and their methods invoked.

With the interface successfully implemented, follow these key steps to integrate it into your application effectively.

• Create an object of the class implementing the interface.
• Call the methods declared in the interface through the object.
• Ensure the methods behave as expected.

Also Read: Career Opportunities in PHP

Step 4: Test and Debug

Finally, test the interface implementation to ensure the class correctly implements the interface's contract. This step is essential to verify that the class provides the required functionality and adheres to the interface's method signatures.

To ensure your interface implementation works seamlessly, follow these critical steps during the testing phase.

• Test the functionality of methods.
• Ensure all required methods are implemented.
• Check for any errors or inconsistencies in method behavior.

Code Example: Simple Interface Implementation

In this example, the process of defining and implementing an interface is demonstrated through a simple scenario where an interface Payment is used to define a method processPayment(). 

Code Snippet:

// Define the Payment interface
interface Payment {
    public function processPayment($amount);  // Method declaration
}

// Implement the Payment interface in the CreditCard class
class CreditCard implements Payment {
    // Implement the processPayment method
    public function processPayment($amount) {
        echo "Processing payment of $" . $amount . " through Credit Card.\n";
    }
}

// Create an object of the CreditCard class
$payment = new CreditCard();
$payment->processPayment(100);  // Output: Processing payment of $100 through Credit Card.

Output:

Processing payment of $100 through Credit Card.

Explanation:

Interface Declaration: The Payment interface is defined with a single method processPayment(), which accepts an amount.

• Class Implementation: The CreditCard class implements the Payment interface and provides a concrete implementation for processPayment().
• Method Execution: The processPayment() method is invoked on an object of the CreditCard class, displaying a message with the payment amount.

This simple example illustrates how to define and implement an interface in PHP. It also highlights how the interface enforces a consistent method signature, ensuring that classes following the interface adhere to the same contract.

Also Read: OOPS Concepts in PHP | Object Oriented Programming in PHP

Now that you've learned how to create an interface in PHP, let's explore how to implement multiple interfaces to enhance flexibility and code organization.

How to Implement Multiple Interfaces in PHP

In PHP, a class can implement multiple interfaces simultaneously. To do so, the interfaces are separated by commas within the implements keyword. This approach allows you to create classes that adhere to the contracts of multiple interfaces.

However, when you use multiple interfaces, following guidelines must be followed to ensure proper functionality and avoid errors. Here’s the breakdown.

• A class can implement more than one interface by separating them with commas.
• This allows the class to adhere to multiple contracts and include the methods from all the interfaces.
• Each method declared in the interfaces must be implemented in the class.

Code Example: Implementing Multiple Interfaces

This example demonstrates how a class implements two interfaces, Payment and Refund, and provides the necessary method implementations for both.

Code Snippet:

// Define the Payment interface
interface Payment {
    public function processPayment(Rs.amount);
}

// Define the Refund interface
interface Refund {
    public function processRefund(Rs.amount);
}

// Implement both Payment and Refund interfaces in the Transaction class
class Transaction implements Payment, Refund {
    // Implement the processPayment method
    public function processPayment(Rs.amount) {
        echo "Processing payment of Rs." . Rs.amount . ".\n";
    }

    // Implement the processRefund method
    public function processRefund(Rs.amount) {
        echo "Processing refund of Rs." . $amount . ".\n";
    }
}

// Create an object of the Transaction class
$transaction = new Transaction();
$transaction->processPayment(150);  // Output: Processing payment of Rs.150.
$transaction->processRefund(50);    // Output: Processing refund of Rs.50.

Output:

Processing payment of Rs.150.
Processing refund of Rs.50.

Explanation:

• Multiple Interfaces: The Transaction class implements both Payment and Refund interfaces, allowing it to adhere to the contracts of both, ensuring consistency and flexibility in handling payments and refunds.
• Method Implementation: Each method defined in the interfaces (processPayment and processRefund) is implemented in the Transaction class, fulfilling the requirements of both interfaces.
• Class Behavior: The Transaction class gains the ability to process payments and refunds, making it versatile for handling financial transactions.
• Code Reusability: By implementing multiple interfaces, the class can easily be extended or adapted for different scenarios, such as integrating additional transaction types in the future.

Now that you understand how to implement multiple interfaces in PHP, it's important to highlight some key considerations and potential pitfalls to be aware of when using this feature.

Key Points About Implementation of Multiple Interfaces

When you implement multiple interfaces in PHP, there are a few important considerations to keep in mind. While PHP allows this flexibility, following some best practices can help prevent common pitfalls. Here’s the breakdown.

• Methods must be public: Any method declared in an interface must be implemented as public in the class. This ensures proper accessibility of the method when used by other components.
• All methods must be implemented: If a class implements multiple interfaces, it must provide implementations for all methods defined in those interfaces. Failure to do so will result in a fatal error.
• No properties in interfaces: Interfaces cannot contain properties. They can only define methods, meaning any shared data must be handled elsewhere in the class.
• Order of implementation doesn't matter: The order in which interfaces are listed when implementing does not affect the class’s behavior. You can list them in any order, and the class will still implement all methods correctly.
• Avoid method name conflicts: When implementing multiple interfaces, ensure there are no conflicting method names between them, as this can lead to ambiguity and errors in your code.

Now that you've learned how to implement multiple interfaces in PHP, let's explore how PHP interfaces can be applied in real-world scenarios to enhance code efficiency and flexibility.

Practical Applications of PHP Interfaces

In PHP, interfaces play a crucial role in real-world applications. They provide structure, ensure consistency, and allow flexibility. Furthermore, interfaces are pivotal when implementing design patterns like Dependency Injection and Strategy, which help maintain loose coupling and increase reusability.

Here are some practical use cases of interfaces in PHP projects:

• Large-Scale Applications: Interfaces help define standardized methods across different modules, making large-scale applications easier to manage and extend.
• Enforcing Consistent Class Structures: Interfaces ensure that developers follow specific patterns, improving code maintainability and readability.
• Dependency Injection: Using interfaces for dependency injection allows flexibility in replacing services without altering the class behavior, enhancing testability.
• Defining APIs: Interfaces are ideal for defining API contracts, ensuring that external services interact with your system consistently.
• Implementing Design Patterns: Design patterns like Strategy and Observer heavily rely on interfaces to decouple algorithms from the classes that use them, increasing modularity.

Now, let’s have a look at some practical examples.

Framework-Specific Examples: Laravel and Symfony

In Laravel, interfaces are heavily used to bind implementations in service providers. This allows for dependency injection and makes services easily swappable.

Example: Binding an interface to an implementation in a Laravel service provider.

Code Snippet:

// Define an interface
interface PaymentGatewayInterface {
    public function processPayment($amount);
}

// Implement the interface in a concrete class
class RazorpayGateway implements PaymentGatewayInterface {
    public function processPayment($amount) {
        echo "Processing payment of Rs.$amount using Razorpay.";
    }
}

// In a Laravel service provider
use Illuminate\Support\ServiceProvider;

class AppServiceProvider extends ServiceProvider {
    public function register() {
        $this->app->bind(PaymentGatewayInterface::class, RazorpayGateway::class);
    }
}

// Using the interface in a controller
class PaymentController {
    protected $gateway;

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

    public function processPayment($amount) {
        $this->gateway->processPayment($amount);
    }
}

// Example usage
$controller = app(PaymentController::class);
$controller->processPayment(1000); // Output: Processing payment of Rs.1000 using Razorpay.

Output: Processing payment of Rs.1000 using Razorpay.

Explanation: In this example:

1. The PaymentGatewayInterface defines a contract for payment gateways.
2. The RazorpayGateway class implements the interface.
3. Laravel’s service container binds the interface to the implementation in the AppServiceProvider.
4. Dependency injection allows the PaymentController to use the RazorpayGateway seamlessly.

Symfony’s Dependency Injection with Interfaces

In Symfony, interfaces are widely used in the dependency injection container to promote flexibility and loose coupling.

Example: Using an interface in a Symfony service.

Code Snippet:

// Define an interface
namespace App\Service;

interface MailerInterface {
    public function sendEmail($recipient, $subject, $message);
}

// Implement the interface in a concrete class
namespace App\Service;

class SmtpMailer implements MailerInterface {
    public function sendEmail($recipient, $subject, $message) {
        echo "Email sent to $recipient with subject '$subject'.";
    }
}

// Configure the service in services.yaml
# config/services.yaml
services:
    App\Service\MailerInterface: '@App\Service\SmtpMailer'

// Use the interface in a controller
namespace App\Controller;

use App\Service\MailerInterface;
use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;

class EmailController extends AbstractController {
    private $mailer;

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

    public function send() {
        $this->mailer->sendEmail('test@example.com', 'Welcome', 'Hello, welcome to Symfony!');
    }
}

// Example usage
$controller = new EmailController(new SmtpMailer());
$controller->send(); // Output: Email sent to test@example.com with subject 'Welcome'.

Output: Email sent to test@example.com with subject 'Welcome'.

Explanation:

1. The MailerInterface defines the contract for sending emails.
2. The SmtpMailer class implements this interface.
3. Symfony’s DI container injects the SmtpMailer into the EmailController, ensuring flexibility.
4. The EmailController uses the interface to send emails, making the implementation interchangeable.

Advanced Use Cases

Interfaces can standardize API integration by defining contracts for HTTP clients.

Example: Creating a contract for an HTTP client.

Code Snippet:

// Define an interface for an HTTP client
interface HttpClientInterface {
    public function get($url);
}

// Implement the interface in a concrete class
class CurlHttpClient implements HttpClientInterface {
    public function get($url) {
        // Simulating an API call
        echo "Fetching data from $url using cURL.";
    }
}

// Use the interface in an API service
class ApiService {
    private $httpClient;

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

    public function fetchData($url) {
        $this->httpClient->get($url);
    }
}

// Example usage
$client = new CurlHttpClient();
$service = new ApiService($client);
$service->fetchData('https://example.com/api'); // Output: Fetching data from https://example.com/api using cURL.

Output: Fetching data from https://example.com/api using cURL.

Explanation: The HttpClientInterface defines the contract for HTTP clients, and the CurlHttpClient provides an implementation. The ApiService uses the interface to fetch data, ensuring that any HTTP client adhering to the interface can be used interchangeably.

Also Read: Polymorphism in PHP Explained with Examples

Building on the practical applications of PHP interfaces, it's clear that their effective use requires adherence to certain guidelines. By following best practices, developers can ensure interfaces remain powerful tools for maintaining code consistency and flexibility.

So, let’s explore the best practices for working with them to ensure efficient and maintainable code.

Best Practices for Working with Interfaces in PHP

When working with interfaces in PHP, following best practices is essential to create clean, maintainable, and scalable code. An interface in PHP should be designed to serve a specific purpose without introducing unnecessary complexity. 

To achieve a structured approach and ensure that interfaces remain effective, adhere to the following practices:

Here are some best practices to consider.

• Keep interfaces focused and minimal: Avoid bloating an interface with unrelated methods. A well-designed interface should focus on a single responsibility.
• Define methods that are universally required by implementing classes: Ensure that the methods in the interface are crucial for all implementing classes, guaranteeing consistent functionality.
• Avoid unnecessary complexity in method declarations: Keep method signatures simple and intuitive. Avoid adding too many parameters or complex logic to the interface methods.
• Use meaningful method names: The methods in an interface should have clear, self-explanatory names, reflecting their role in the implementation.
• Use interfaces for abstraction, not implementation: Interfaces in OOP should define "what" needs to be done, not "how" it is done. Leave the implementation details to the classes.

To ensure interfaces in PHP are used effectively, it's equally important to understand common pitfalls that can arise and how to avoid them.

Common Pitfalls When Using Interfaces in PHP

While interfaces are powerful tools in object-oriented programming, misusing them can lead to inefficient and unmanageable code. Here are common mistakes and actionable advice to avoid them.

Having explored the best practices for working with interfaces in PHP, it's essential to understand the fundamental differences between interfaces and abstract classes in OOPs.

Interface in OOPs vs Abstract Class: Key Differences

When it comes to object-oriented programming (OOP) in PHP, both interfaces and abstract classes play important roles. However, understanding the differences between the two is essential for effective and efficient coding. 

The key distinctions between interfaces and abstract classes become evident when considering their structure, usage, and limitations.

To clarify these differences, here's a comparison table that highlights key features:

Now, to further demonstrate the differences, let’s look at code examples for both an interface in OOP and an abstract class.

Code Example: 

Interface Example

This code demonstrates how an interface in PHP defines methods that must be implemented by a class.

Code Snippet:

// Interface definition
interface Animal {
    public function makeSound();
}

// Class implementing the interface
class Dog implements Animal {
    public function makeSound() {
        echo "Bark!";
    }
}

// Instantiate the class
$dog = new Dog();
$dog->makeSound(); // Output: Bark!

Output: 

Bark!

Explanation: In this example, the Animal interface defines the makeSound method, but does not provide an implementation. The Dog class implements the Animal interface and provides its own implementation of the makeSound method. 

The output shows that the method works as expected, making it clear that the Dog class adheres to the contract defined by the Animal interface.

Also Read: What Is Externalization In Java? Interface, Features & Example

Abstract Class Example

Now, here's an example that shows how an abstract class can be used to define both abstract and concrete methods.

Code Snippet:

// Abstract class definition
abstract class Animal {
    // Abstract method (must be implemented by subclasses)
    abstract public function makeSound();

    // Concrete method (shared functionality)
    public function sleep() {
        echo "Sleeping...";
    }
}

// Class extending the abstract class
class Dog extends Animal {
    public function makeSound() {
        echo "Bark!";
    }
}

// Instantiate the class
$dog = new Dog();
$dog->makeSound(); // Output: Bark!
$dog->sleep();     // Output: Sleeping...

Output:

Bark!
Sleeping...

Explanation: In this example, the Animal abstract class contains both an abstract method (makeSound) and a concrete method (sleep). The Dog class extends the abstract class and provides its own implementation for the makeSound method. 

The output shows that the class inherits both the required abstract method and the optional concrete method.

Also Read: Abstract Class and Methods in Java: Key Concepts, Examples and Best Practices

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