Top PHP Interview Questions 2025 - Beginner to Advanced

1. What is the difference between == and === in PHP?

Answer:

• == checks if values are equal, but not types.

• === checks if values are equal and of the same type.

Example:

$a = 5;       // integer $b = '5';     // string var_dump($a == $b);  // true var_dump($a === $b); // false

Explanation:
$a == $b is true because both are 5.
But $a === $b is false because one is an integer and the other is a string.

2. What are traits in PHP and why are they used?

Answer:
Traits are like reusable chunks of code. PHP doesn't support multiple inheritance (a class extending two classes), but traits let you use methods from multiple sources.

Example:

trait Logger {     public function log($msg) {         echo "Log: $msg";     } } class MyClass {     use Logger; } $obj = new MyClass(); $obj->log("Hello!"); 

Explanation:
Here, the Logger trait gives the log() method to MyClass, without inheritance. You can reuse traits across many classes.

3. What is late static binding in PHP?

Answer:
Late static binding allows you to reference the called class, not the class where the method was originally defined.

Example:

class A {
    public static function who() {
        echo __CLASS__;
    }

    public static function test() {
        static::who(); // late static binding
    }
}

class B extends A {
    public static function who() {
        echo __CLASS__;
    }
}

B::test(); // Outputs: B

Explanation:
If we used self::who(), it would print A. But static::who() refers to the calling class (B), thanks to late static binding.

4. What are generators in PHP?

Answer:
Generators are like lightweight iterators. They help loop over data without loading everything into memory.

Example:

function countUpTo($n) {     for ($i = 1; $i <= $n; $i++) {         yield $i;     } } foreach (countUpTo(5) as $num) {     echo $num . " "; }

Explanation:
Instead of returning all values at once, yield returns one value at a time. It’s memory efficient for large data sets.

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

Answer:
These are access modifiers for class members (properties or methods):

• public – accessible from anywhere.

• protected – accessible only inside the class and its child classes.

• private – accessible only inside the class itself.

Example:

class Test {
    public $a = "Public";
    protected $b = "Protected";
    private $c = "Private";

    public function show() {
        echo $this->a . ", " . $this->b . ", " . $this->c;
    }
}

$obj = new Test();
$obj->show();     // Works
echo $obj->a;     // Works
// echo $obj->b;  // Error
// echo $obj->c;  // Error

Explanation:
You can access $a from outside. $b and $c are protected/private, so direct access gives an error.

6. What is the use of final keyword in PHP?

Answer:
The final keyword prevents class or method from being overridden.

Example:

class A {
    final public function hello() {
        echo "Hello";
    }
}

class B extends A {
    // public function hello() {} // Error!
}

Explanation:
You can't override the hello() method in class B because it's marked final.

7. What is the use of the __call() magic method in PHP?

Answer:
__call() is triggered when calling an undefined method in an object.

Example:

class Magic {
    public function __call($name, $arguments) {
        echo "Calling method '$name' with arguments: " . implode(', ', $arguments);
    }
}

$obj = new Magic();
$obj->sayHello("World");  // sayHello is not defined

Explanation:
Even though sayHello is not defined, __call() catches it and handles the call gracefully.

8. How can you handle errors in PHP using try-catch?

Answer:
Use try-catch to handle exceptions and avoid fatal errors.

Example:

try {
    if (!file_exists("test.txt")) {
        throw new Exception("File not found!");
    }
} catch (Exception $e) {
    echo "Caught error: " . $e->getMessage();
}

Explanation:
If test.txt is missing, it throws an exception. The catch block handles it, preventing a crash.

9. What is Dependency Injection in PHP?

Answer:
Dependency Injection is a design pattern where a class gets its dependencies from outside, not by creating them itself.

Example:

class Logger {
    public function log($msg) {
        echo $msg;
    }
}

class UserService {
    private $logger;

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

    public function createUser() {
        $this->logger->log("User created!");
    }
}

$logger = new Logger();
$service = new UserService($logger);
$service->createUser();

Explanation:
UserService doesn’t create a Logger. It receives it via the constructor. This makes testing and managing dependencies easier.

10. What is the difference between abstract class and interface in PHP?

Answer:

Example:

interface Shape {
    public function getArea();
}

abstract class Polygon {
    public function sayHi() {
        echo "Hi from Polygon!";
    }
}

class Rectangle extends Polygon implements Shape {
    public function getArea() {
        return 10 * 20;
    }
}

Explanation:

• Interface is like a contract.

• Abstract class gives some shared functionality.

• You can implement multiple interfaces but only extend one abstract class.

11. What is the difference between include, require, include_once, and require_once in PHP?
Answer:
These are used to include files in PHP, but they differ in error handling and repeat inclusion.

• include → throws a warning if the file is not found.

• require → throws a fatal error and stops execution if the file is not found.

• include_once / require_once → ensures the file is included only once.

Example:

include 'file.php';         // Warning if missing require 'file.php';         // Fatal error if missing include_once 'file.php';    // Included only once require_once 'file.php';    // Included only once

Explanation:
Use require when the file is essential. Use include for optional files.

12. What is the difference between static and non-static methods in PHP?
Answer:

• Static methods can be called without creating an object.

• Non-static methods require object instantiation.

Example:

class MyClass {     public static function sayHi() {         echo "Hi!";     }     public function sayHello() {         echo "Hello!";     } } MyClass::sayHi();              // Static method $obj = new MyClass(); $obj->sayHello();              // Non-static method

Explanation:
Static methods are used for utility-style functions that don’t depend on object state.

13. What is an anonymous function (closure) in PHP?
Answer:
An anonymous function is a function without a name, often used for short-lived operations or callbacks.

Example:

$greet = function($name) {     return "Hello, $name!"; }; echo $greet("John");

Explanation:
Closures can be stored in variables, passed as parameters, and even use variables from outside using use.

14. What is namespacing in PHP and why use it?
Answer:
Namespaces prevent class and function name collisions.

Example:

namespace App\Models; class User {     public function getName() {         return "John";     } } // Usage $user = new \App\Models\User();

Explanation:
Namespaces are essential for organizing code in large applications.

15. What is the SPL in PHP?
Answer:
SPL = Standard PHP Library. It provides a collection of interfaces and classes for common data structures (like LinkedList, Stack, etc).

Example:

$stack = new SplStack(); $stack->push("First"); $stack->push("Second"); echo $stack->pop(); // Second

Explanation:
SPL helps manage data structures without implementing them manually.

16. How do you use type declarations in PHP?
Answer:
Type declarations enforce variable types for function parameters and return types.

Example:

function add(int $a, int $b): int {     return $a + $b; } echo add(5, 3);  // Outputs: 8

Explanation:
This helps catch bugs early by ensuring the correct data types are used.

17. What is object cloning in PHP?
Answer:
Cloning creates a shallow copy of an object using the clone keyword.

Example:

class MyClass {     public $name = "Original"; } $a = new MyClass(); $b = clone $a; $b->name = "Cloned"; echo $a->name;  // Original echo $b->name;  // Cloned

Explanation:
Each object becomes independent after cloning.

18. What is the difference between isset(), empty(), and is_null()?
Answer:

• isset() → checks if variable is set and not null.

• empty() → checks if variable is empty.

• is_null() → checks if variable is null.

Example:

$var = 0; var_dump(isset($var));    // true var_dump(empty($var));    // true var_dump(is_null($var));  // false

Explanation:
Use them according to what you're testing — existence, emptiness, or nullness.

examples, continuing in the same format:

19. What is the use of the __get() and __set() magic methods in PHP?
Answer:
These magic methods are triggered when accessing or assigning values to inaccessible (private/protected/non-existent) properties.

Example:

class Demo {     private $data = [];     public function __get($name) {         return $this->data[$name] ?? "Not found";     }     public function __set($name, $value) {         $this->data[$name] = $value;     } } $obj = new Demo(); $obj->name = "PHP"; echo $obj->name;  // Output: PHP

Explanation:
They allow dynamic handling of properties and can be used for proxies or ORM models.

20. What is the difference between session and cookie in PHP?
Answer:

• Session stores data on the server.

• Cookie stores data in the user’s browser.

Example:

// Cookie setcookie("user", "John", time() + 3600); // Session session_start(); $_SESSION["user"] = "John";

Explanation:
Sessions are more secure; cookies are suitable for persistent lightweight data.

21. How does PHP handle references (&) and what is their use?
Answer:
References allow two variables to point to the same data.

Example:

$a = "Hello"; $b = &$a; $b = "World"; echo $a;  // Output: World

Explanation:
Useful when you want one variable to reflect changes in another, like passing by reference in functions.

22. What is the difference between unset() and null in PHP?
Answer:

• unset() destroys the variable.

• Setting a variable to null keeps it declared but with no value.

Example:

$a = "Hello"; unset($a);     // $a is no longer set $b = "World"; $b = null;     // $b is still set, but null

Explanation:
Use unset() to remove variables completely.

23. What is the use of the yield from expression in PHP?
Answer:
yield from is used to delegate part of a generator to another generator.

Example:

function gen1() {     yield 1;     yield 2; } function gen2() {     yield from gen1();     yield 3; } foreach (gen2() as $val) {     echo $val . " ";  // Output: 1 2 3 }

Explanation:
Makes code cleaner by reducing nested loops in generators.

24. What are weak references in PHP and when to use them?
Answer:
A weak reference allows referencing an object without preventing it from being garbage-collected.

Example:

$obj = new stdClass(); $weakRef = WeakReference::create($obj); unset($obj); var_dump($weakRef->get());  // NULL

Explanation:
Useful in caching systems where you don’t want to prevent object cleanup.

25. What is the purpose of array_map() in PHP?
Answer:
array_map() applies a callback to each element in one or more arrays.

Example:

$numbers = [1, 2, 3]; $squares = array_map(fn($n) => $n * $n, $numbers); print_r($squares);  // [1, 4, 9]

Explanation:
It’s a functional approach to manipulating arrays.

26. How to create and use a custom exception in PHP?
Answer:
Extend the base Exception class to define your own exception type.

Example:

class MyException extends Exception {} try {     throw new MyException("Custom error!"); } catch (MyException $e) {     echo $e->getMessage();  // Output: Custom error! }

Explanation:
Custom exceptions help categorize and handle specific error types.

27. What is the difference between explode() and str_split()?
Answer:

• explode() splits a string by a delimiter.

• str_split() splits a string into chunks (by length).

Example:

$str = "a,b,c"; print_r(explode(",", $str));   // ['a', 'b', 'c'] $str2 = "hello"; print_r(str_split($str2, 2));  // ['he', 'll', 'o']

Explanation:
Use based on whether you're splitting by characters or delimiters.

28. What is the difference between foreach and each() in PHP?
Answer:

• foreach is a modern loop for arrays.

• each() was used to return the current key-value pair and move the pointer (deprecated in PHP 7.2+).

Example (foreach):

$arr = ["a" => 1, "b" => 2]; foreach ($arr as $key => $value) {     echo "$key => $value "; }

Explanation:
Avoid each() in modern code; prefer foreach for readability and compatibility.

29. What is a recursive function in PHP?
Answer:
A function that calls itself to solve smaller sub-problems.

Example:

function factorial($n) {     return $n <= 1 ? 1 : $n * factorial($n - 1); } echo factorial(5); // Output: 120

Explanation:
Used in problems like factorial, tree traversal, etc.

30. What is the difference between array_merge() and array_merge_recursive()?
Answer:

• array_merge() overwrites values with the same key.

• array_merge_recursive() merges them into arrays.

Example:

$a = ['color' => 'red']; $b = ['color' => 'blue']; print_r(array_merge($a, $b));           // ['color' => 'blue'] print_r(array_merge_recursive($a, $b)); // ['color' => ['red', 'blue']]

Explanation:
Use recursive merge when you want to retain all values.

31. How to serialize and unserialize data in PHP?
Answer:
Used to convert objects/arrays into a storable string format.

Example:

$data = ['name' => 'John']; $serialized = serialize($data); $unserialized = unserialize($serialized); print_r($unserialized);

Explanation:
Used in sessions, caching, or storing complex data structures.

31. What is the difference between array_filter() and array_map()?
Answer:

• array_filter() removes elements based on condition.

• array_map() modifies each element.

Example:

$nums = [1, 2, 3, 4]; $even = array_filter($nums, fn($n) => $n % 2 === 0); // [2, 4] $squared = array_map(fn($n) => $n * $n, $nums);      // [1, 4, 9, 16]

Explanation:
Filter = keep only what matches. Map = change values.

32. What is the difference between isset() and empty() in PHP?
Answer:

• isset() checks if a variable is set and not null.

• empty() checks if a variable is empty (0, '', null, false, etc.)

Example:

$a = 0; var_dump(isset($a));  // true var_dump(empty($a));  // true

Explanation:
isset() won’t return false for falsy values like 0, while empty() will.

33. What is the Null Coalescing Operator (??) in PHP?
Answer:
It returns the first operand if it's set and not null; otherwise, returns the second.

Example:

$name = $_GET['name'] ?? 'Guest'; echo $name;

Explanation:
It’s a shorthand for isset($var) ? $var : default.

34. How to prevent SQL Injection in PHP?
Answer:
Use prepared statements with parameter binding.

Example (PDO):

$pdo = new PDO($dsn, $user, $pass); $stmt = $pdo->prepare("SELECT * FROM users WHERE email = ?"); $stmt->execute([$email]);

Explanation:
Prepared statements ensure user input is properly escaped, preventing injection.

35. What is the difference between include, require, include_once, and require_once?
Answer:

• include gives a warning if the file is missing, script continues.

• require gives a fatal error, script stops.

• _once ensures the file is included only once.

Example:

include 'file.php'; require 'file.php'; include_once 'file.php'; require_once 'file.php';

Explanation:
Use require_once for essential files to avoid multiple inclusions.

36. What is overloading and overriding in PHP OOP?
Answer:

• Overloading: Using magic methods (__get, __set, __call) to dynamically create properties/methods.

• Overriding: Redefining a parent class method in a child class.

Example (Overriding):

class A {     public function greet() {         echo "Hello";     } } class B extends A {     public function greet() {         echo "Hi";     } } $obj = new B(); $obj->greet();  // Hi

Explanation:
Overriding customizes base class behavior, while overloading adds dynamic flexibility.

37. What are anonymous classes in PHP?
Answer:
Anonymous classes are one-off class definitions used when you don't need to reuse them.

Example:

$greeting = new class {     public function say() {         return "Hello from anonymous class!";     } }; echo $greeting->say();

Explanation:
Anonymous classes help when you need a simple class implementation without naming or reuse.

38. What is the difference between explode() and str_split() in PHP?
Answer:

• explode() splits a string by a delimiter into an array.

• str_split() splits a string into individual characters or chunks of specified length.

Example:

$str = "Hello,World"; print_r(explode(",", $str));    // ['Hello', 'World'] print_r(str_split($str, 2));    // ['He', 'll', 'o,', 'Wo', 'rl', 'd']

Explanation:
Use explode() when breaking a string by a known separator. Use str_split() for character-level operations.

39. What is array_walk() in PHP?
Answer:
array_walk() applies a user-defined function to every element of an array.

Example:

$arr = [1, 2, 3]; array_walk($arr, function (&$value, $key) {     $value *= 2; }); print_r($arr); // [2, 4, 6]

Explanation:
Useful for applying transformations with reference access to each value.

40. What is a Closure in PHP?
Answer:
A Closure is an anonymous function that can capture variables from the parent scope.

Example:

$multiplier = 3; $multiply = function ($n) use ($multiplier) {     return $n * $multiplier; }; echo $multiply(5); // 15

Explanation:
Closures are commonly used in callbacks, array functions, and functional programming.

41. How does PHP handle timezones and date formatting?
Answer:
PHP uses the DateTime class and date_default_timezone_set() for timezones.

Example:

date_default_timezone_set('Asia/Kolkata'); $dt = new DateTime(); echo $dt->format('Y-m-d H:i:s');

Explanation:
Using DateTime gives you timezone-aware, formatted, and manipulable date/time values.

42. What is the difference between unset() and null assignment in PHP?
Answer:

• unset() destroys the variable.

• Assigning null just empties its value.

Example:

$a = 5; unset($a);  // Variable is removed $b = 5; $b = null;  // Variable still exists, value is null

Explanation:
isset($a) will return false after unset(), but true for a variable set to null.

43. What are callable types in PHP?
Answer:
Callable types are functions/methods passed as variables, closures, or arrays.

Example:

function greet($name) {     return "Hello, $name"; } $call = 'greet'; echo $call('John'); // Hello, John

Explanation:
Useful for callbacks, array functions, and flexible APIs.

44. How do you make a class iterable in PHP?
Answer:
Implement the Iterator or IteratorAggregate interface.

Example:

class MyList implements IteratorAggregate {     private $items = [1, 2, 3];     public function getIterator(): Traversable {         return new ArrayIterator($this->items);     } } $obj = new MyList(); foreach ($obj as $item) {     echo $item . " "; }

Explanation:
This allows your objects to be used in foreach just like arrays.

45. What is __autoload() and how is it replaced in modern PHP?
Answer:

• __autoload() is an old method for loading undefined classes automatically.

• Replaced by spl_autoload_register() in modern PHP.

Example:

spl_autoload_register(function ($class) {     include "classes/$class.php"; });

Explanation:
Modern autoloading allows registering multiple loaders and is compatible with Composer and PSR standards.

46. How do you handle large file uploads in PHP?
Answer:

1. Update php.ini:

   • upload_max_filesize

   • post_max_size

   • max_execution_time

2. Use chunked uploads or background processing for huge files.

Explanation:
PHP has built-in limits for safety. For large files, it's common to handle chunks and optimize memory usage.

47. What is the use of __toString() magic method in PHP?
Answer:
Allows an object to be treated as a string.

Example:

class Book {     public $title = "PHP Guide";     public function __toString() {         return $this->title;     } } $book = new Book(); echo $book; // Output: PHP Guide

Explanation:
When an object is used in a string context, __toString() is automatically called.