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

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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;
}

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🔹 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.

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🔹 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.

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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.

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🔹 6. How do you handle errors and exceptions in PHP?

Answer:
Use try...catch for exceptions. Custom error handling with set_error_handler().

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🔹 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

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🔹 8. What are magic methods in PHP?

Answer:
Special methods with __ prefix. E.g.:

• __construct(), __destruct()
• __get(), __set(), __call()
• __toString()

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Top 30 PHP Interview Questions and Answers

🔹 9. What is the difference between public, private, and protected in PHP?

Answer:

• public: Accessible anywhere
• protected: Accessible in class & subclass
• private: Accessible only within class

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🔹 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;
  }
}

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🔹 11. Explain differences between abstract class and interface.

Answer:

• abstract: Can have implemented methods.
• interface: Only method declarations.

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🔹 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.

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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 {}

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🔹 14. How do you handle large file uploads in PHP?

Answer:

• Increase upload_max_filesize, post_max_size in php.ini
• Use move_uploaded_file()
• Validate file types and size

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🔹 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)

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🔹 16. What are the types of arrays in PHP?

Answer:

• Indexed
• Associative
• Multidimensional

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🔹 17. What is the difference between explode() and implode()?

Answer:

• explode(): Converts string to array
• implode(): Converts array to string

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🔹 18. How do you secure PHP web applications?

Answer:

• Escape output (XSS protection)
• Use prepared statements (SQLi protection)
• Use htmlspecialchars(), strip_tags()
• CSRF tokens

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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";
};

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🔹 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)

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🔹 21. How does PHP handle memory management?

Answer:
PHP uses a Garbage Collector (GC) to manage memory, especially for cyclic references.

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🔹 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;
}

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Top 30 PHP Interview Questions and Answers

🔹 23. What are common design patterns used in PHP?

Answer:

• Singleton
• Factory
• Strategy
• Repository
• MVC
• Dependency Injection

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🔹 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;
};

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🔹 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();

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🔹 26. What is the use of final keyword in PHP?

Answer:

• A final class can’t be extended.
• A final method can’t be overridden.

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🔹 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++; }
}

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🔹 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();

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🔹 29. What’s the difference between foreach and each() in PHP?

Answer:

• foreach is modern and safe.
• each() is deprecated in PHP 7.2+, previously used with while.

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🔹 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