Here are Top 30 PHP Interview Questions and Answers for Experienced Developers (3+ years experience), covering advanced concepts.
🔹 1. What is the difference between == and === in PHP?
Answer:
==compares values only (type juggling allowed).===compares both value and type.
5 == '5' // true
5 === '5' // false
Top 30 PHP Interview Questions and Answers
🔹 2. What are Traits in PHP?
Answer:
Traits allow code reuse in single inheritance. They are similar to abstract classes but more flexible.
trait Logger {
public function log($msg) {
echo $msg;
}
}
class App {
use Logger;
}
🔹 3. How is a session different from a cookie in PHP?
Answer:
- Session: Stored on server, expires after browser is closed.
- Cookie: Stored in browser, with set expiration.
🔹 4. Explain PHP autoloading and PSR-4 standard.
Answer:
Autoloading loads classes on demand using spl_autoload_register().
PSR-4 is a standard for autoloading using namespaces and directory structure.
Top 30 PHP Interview Questions and Answers
🔹 5. What is the difference between include, require, include_once, and require_once?
Answer:
include– Warning if file not found.require– Fatal error if file not found.*_once– Loads only once even if included multiple times.
🔹 6. How do you handle errors and exceptions in PHP?
Answer:
Use try...catch for exceptions. Custom error handling with set_error_handler().
🔹 7. How can you improve PHP script performance?
Answer:
- Use Opcode caching (e.g. OPcache)
- Use autoloaders
- Avoid unnecessary database calls
- Optimize SQL queries
- Use array caching or Redis
🔹 8. What are magic methods in PHP?
Answer:
Special methods with __ prefix. E.g.:
__construct(),__destruct()__get(),__set(),__call()__toString()
Top 30 PHP Interview Questions and Answers
🔹 9. What is the difference between public, private, and protected in PHP?
Answer:
public: Accessible anywhereprotected: Accessible in class & subclassprivate: Accessible only within class
🔹 10. How do you implement Dependency Injection in PHP?
Answer:
Inject dependencies via constructor, method, or setter.
class Logger {}
class User {
private $logger;
public function __construct(Logger $logger) {
$this->logger = $logger;
}
}
🔹 11. Explain differences between abstract class and interface.
Answer:
abstract: Can have implemented methods.interface: Only method declarations.
🔹 12. What is Composer? How does it help in PHP?
Answer:
Composer is a dependency manager for PHP.
Helps include and manage packages via composer.json.
Top 30 PHP Interview Questions and Answers
🔹 13. What is Namespacing in PHP?
Answer:
Namespaces avoid class/function name collisions.
namespace App\Models;
class User {}
🔹 14. How do you handle large file uploads in PHP?
Answer:
- Increase
upload_max_filesize,post_max_sizeinphp.ini - Use
move_uploaded_file() - Validate file types and size
🔹 15. What is the difference between GET and POST in PHP?
Answer:
- GET: Appends data in URL (visible)
- POST: Sends data in request body (secure for sensitive info)
🔹 16. What are the types of arrays in PHP?
Answer:
- Indexed
- Associative
- Multidimensional
🔹 17. What is the difference between explode() and implode()?
Answer:
explode(): Converts string to arrayimplode(): Converts array to string
🔹 18. How do you secure PHP web applications?
Answer:
- Escape output (XSS protection)
- Use prepared statements (SQLi protection)
- Use
htmlspecialchars(),strip_tags() - CSRF tokens
Top 30 PHP Interview Questions and Answers
🔹 19. What are anonymous functions and closures?
Answer:
Functions without names. Useful for callbacks.
$greet = function($name) {
return "Hello $name";
};
🔹 20. What is the difference between isset() and empty()?
Answer:
isset(): True if variable exists and not null.empty(): True if variable is empty (null, 0, “”, false)
🔹 21. How does PHP handle memory management?
Answer:
PHP uses a Garbage Collector (GC) to manage memory, especially for cyclic references.
🔹 22. What are generators in PHP?
Answer:
Generators allow you to iterate over data without storing it all in memory.
function getNumbers() {
for ($i = 0; $i < 1000; $i++) yield $i;
}
Top 30 PHP Interview Questions and Answers
🔹 23. What are common design patterns used in PHP?
Answer:
- Singleton
- Factory
- Strategy
- Repository
- MVC
- Dependency Injection
🔹 24. What is a Closure and how can it access outer variables?
Answer:
A closure is an anonymous function that can use variables from parent scope via use.
$val = 5;
$fn = function() use ($val) {
return $val * 2;
};
🔹 25. How to connect PHP with MySQL using PDO?
Answer:
$pdo = new PDO("mysql:host=localhost;dbname=test", "user", "pass");
$stmt = $pdo->prepare("SELECT * FROM users");
$stmt->execute();
🔹 26. What is the use of final keyword in PHP?
Answer:
- A
final classcan’t be extended. - A
final methodcan’t be overridden.
🔹 27. What are static methods and properties in PHP?
Answer:
Belong to the class, not instance. Use self:: to call.
class A {
public static $count = 0;
public static function inc() { self::$count++; }
}
🔹 28. What is output buffering in PHP?
Answer:
Buffers output until script finishes or ob_flush() is called.
ob_start();
echo "Hello";
$content = ob_get_clean();
🔹 29. What’s the difference between foreach and each() in PHP?
Answer:
foreachis modern and safe.each()is deprecated in PHP 7.2+, previously used withwhile.
🔹 30. What is the use of __invoke() method in PHP?
Answer:
Allows an object to be used as a callable.
class Test {
public function __invoke($x) {
return $x * 2;
}
}
$t = new Test();
echo $t(5); // 10
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Top 30 PHP Interview Questions and Answers
