How does the usage of abstract classes and interfaces impact code flexibility and maintainability in PHP?

Using abstract classes and interfaces in PHP can greatly enhance code flexibility and maintainability. Abstract classes allow you to define common methods that must be implemented by subclasses, providing a clear structure for your code. Interfaces define a contract that classes must adhere to, allowing for polymorphism and easier swapping of implementations. By utilizing these features, you can create more modular and extensible code that is easier to maintain and update. 

```php
<?php

// Define an interface
interface Logger {
    public function log($message);
}

// Implement the interface in a class
class FileLogger implements Logger {
    public function log($message) {
        // Log message to a file
    }
}

// Create a class that uses the Logger interface
class UserManager {
    private $logger;

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

    public function addUser($user) {
        // Add user logic

        // Log the action
        $this->logger->log('User added: ' . $user);
    }
}

// Create an instance of the FileLogger and pass it to the UserManager
$fileLogger = new FileLogger();
$userManager = new UserManager($fileLogger);

$userManager->addUser('John Doe');
```
In this example, we define a Logger interface and a FileLogger class that implements this interface. We then create a UserManager class that takes a Logger object in its constructor. This allows us to easily swap out different logger implementations without changing the UserManager class, making our code more flexible and maintainable.

Keywords

abstract classes interfaces code flexibility maintainability PHP

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