PHP  Interview Questions and Answers

​

1. What is Dependency Injection in PHP?

   • Answer: Dependency Injection is a design pattern used to reduce coupling between objects by passing dependencies (objects or services) to a class rather than having the class create them itself. This helps improve code maintainability, testing, and flexibility.

2. Explain the concept of Autoloading in PHP.

   • Answer: Autoloading in PHP is the process of automatically loading class files when they are needed, instead of manually including or requiring the class file. PHP provides functions like spl_autoload_register() to register an autoloader function that can automatically load classes on demand.

3. What are PSR standards?

   • Answer: PSR (PHP Standards Recommendations) are a set of guidelines and best practices aimed at improving interoperability and coding consistency across PHP projects. Common PSRs include PSR-1 (Basic Coding Standard), PSR-2 (Coding Style Guide), PSR-4 (Autoloading Standard), and PSR-7 (HTTP Message Interface).

4. What is the difference between yield and return in PHP?

   • Answer: yield is used in a generator function to produce a value without returning it, allowing the function to be paused and resumed. return exits a function and returns a value. Generators with yield are useful for working with large datasets because they produce values on the fly without using memory to store them.

5. What are some benefits of using the mysqli extension over mysql_* functions?

   • Answer: The mysqli extension provides several advantages over the deprecated mysql_* functions:

     • Support for prepared statements (improving security against SQL injection).

     • Object-oriented API.

     • Support for multiple statements.

     • Enhanced error handling and reporting.

     • Transaction support.

6. What is the significance of PDO::ATTR_ERRMODE in PHP?

   • Answer: PDO::ATTR_ERRMODE is a constant used to configure the error handling mode for a PDO instance. It can be set to one of the following:

     • PDO::ERRMODE_SILENT (default) – No error reporting.

     • PDO::ERRMODE_WARNING – Generates warnings.

     • PDO::ERRMODE_EXCEPTION – Throws exceptions (recommended for most use cases).

7. What are the benefits of using Composer in PHP?

   • Answer: Composer is a dependency manager for PHP that allows you to manage libraries and packages. Benefits include:

     • Automatically managing project dependencies and versions.

     • Supporting autoloading to include necessary files without manual require or include calls.

     • Easy integration with external libraries.

     • Simplified package installation and updates via composer install and composer update.

8. What are the key differences between public, protected, and private properties and methods in PHP?

   • Answer:

     • public: Accessible from anywhere, inside or outside the class.

     • protected: Accessible only within the class and by subclasses (child classes).

     • private: Accessible only within the class that defines the property or method.

9. Explain the concept of traits in PHP and their use cases.

   • Answer: Traits are a way of reusing code in multiple classes without the limitations of single inheritance. Traits are used when you need to share methods between classes without requiring them to be subclasses. They allow code reuse and help avoid duplication.

10. What is the purpose of __get() and __set() magic methods in PHP?

    • Answer: The __get() and __set() magic methods are used to intercept and manage access to undefined or inaccessible object properties. __get() is triggered when trying to read an undefined property, and __set() is triggered when trying to write to an undefined property.

11. Explain the difference between final and abstract in PHP.

    • Answer:

      • final: Used to prevent class inheritance or method overriding.

      • abstract: Used to define methods in abstract classes that must be implemented by child classes.

12. What is the spl_object_hash() function used for in PHP?

    • Answer: The spl_object_hash() function returns a unique identifier for a given object. It is used when you need to compare objects or need a unique hash of an object during operations like caching.

13. Explain the __call() magic method in PHP.

    • Answer: The __call() magic method is triggered when invoking a method that does not exist in the object. It allows you to catch method calls dynamically and handle them programmatically, such as implementing a proxy pattern or forwarding the call to another object.

14. What are anonymous functions (closures) in PHP?

    • Answer: Anonymous functions, also known as closures, are functions that do not have a name. They can be passed as arguments to other functions or assigned to variables. They can also capture variables from the surrounding scope, making them useful for callbacks and functional programming techniques.

15. What is the array_walk() function in PHP?

    • Answer: The array_walk() function applies a user-defined function to each element of an array. It is used for modifying array elements in place. Example usage: array_walk($array, function(&$item) { $item = strtoupper($item); });

16. What is the difference between session_start() and session_regenerate_id()?

    • Answer:

      • session_start() starts a session or resumes an existing one.

      • session_regenerate_id() is used to generate a new session ID. It helps prevent session fixation attacks by changing the session ID during session management.

17. How can you protect against SQL injection in PHP?

    • Answer: You can protect against SQL injection by:

      • Using prepared statements with mysqli or PDO.

      • Escaping input data using mysqli_real_escape_string() (if not using prepared statements).

      • Validating and sanitizing user input before using it in queries.

18. What is the __destruct() magic method in PHP?

    • Answer: The __destruct() method is automatically called when an object is destroyed or goes out of scope. It is typically used to perform cleanup tasks, such as closing database connections or freeing resources.

19. What is the purpose of filter_var() in PHP?

    • Answer: filter_var() is a function used to sanitize or validate data. It can validate email addresses, URLs, IP addresses, and more. It helps ensure the integrity and security of user input.

20. What is a Singleton pattern in PHP?

    • Answer: The Singleton pattern ensures that a class has only one instance, and provides a global point of access to that instance. This is typically used for managing shared resources like database connections or configuration settings.

21. What is the array_reduce() function in PHP?

    • Answer: The array_reduce() function iterates over an array, applying a user-defined callback function to reduce the array to a single value. It is commonly used for calculating totals or aggregating data.

22. How do you implement custom exceptions in PHP?

    • Answer: To implement custom exceptions, you extend the built-in Exception class. This allows you to define your own exception types with custom error messages and handling mechanisms.

      class MyException extends Exception { public function errorMessage() { return "Error: " . $this->getMessage(); } }

23. Explain the __clone() magic method in PHP.

    • Answer: The __clone() magic method is used when an object is cloned using the clone keyword. It allows you to define custom behavior when cloning an object, such as deep copying properties or resetting certain attributes.

24. What is an abstract class and how does it differ from an interface in PHP?

    • Answer:

      • An abstract class can have both abstract methods (without implementation) and concrete methods (with implementation). It cannot be instantiated directly.

      • An interface defines only method signatures and cannot provide any implementation. A class can implement multiple interfaces but can only extend one abstract class.

25. What is the purpose of mysqli_multi_query()?

    • Answer: mysqli_multi_query() is used to execute multiple SQL queries in a single function call. This is helpful for batch processing or running multiple queries in a transaction.

These advanced PHP questions focus on design patterns, security practices, database management, and deeper language features, which are essential for senior-level PHP development.