Interview Q&A

Pick a topic — languages & databases — 100+ questions and answers in the center column.

Calculators Salary Emoji Website tools ← Listings

PHP

Interview questions & answers

Server-side scripting, Laravel-style topics, runtime.

102 questions

Question 1
What is PHP?
A server-side scripting language embedded in HTML; executes on the server and outputs HTML. Common stacks: LAMP, Laravel/Symfony apps.
Example code
```
<?php
echo "Hello, PHP\n";
```
Question 2
What is the difference between == and === in PHP?
== compares with type juggling; === compares type and value. Prefer === to avoid surprising coercion.
Example code
```
<?php
var_dump(0 == "0", 0 === "0");
```
Question 3
What are PHP superglobals?
$_GET, $_POST, $_SESSION, $_COOKIE, $_SERVER, $_FILES, $_ENV, $_REQUEST, $GLOBALS—built-in arrays for HTTP and runtime context.
Example code
```
<?php
echo $_SERVER["REQUEST_METHOD"] ?? "CLI";
```
Question 4
include vs require?
Both pull in files; require throws fatal error on failure, include emits warning. _once variants skip if already loaded.
Example code
```
<?php
require_once __DIR__ . "/config.php";
```
Question 5
What is autoloading?
spl_autoload_register or Composer PSR-4 maps class names to files so you don't manual require every class.
Example code
```
<?php
spl_autoload_register(fn($c) => require str_replace("\\", "/", $c) . ".php");
```
Question 6
What is Composer?
Dependency manager for PHP: composer.json declares packages; vendor/ and autoload.php wire class loading.
Example code
```
<?php
// composer require vendor/autoload.php
```
Question 7
What is a namespace?
Avoids class name collisions; use statement imports symbols. PSR-4 ties namespaces to directory paths.
Example code
```
<?php
namespace App\Models;
class User {}
```
Question 8
public, protected, private?
Visibility for properties/methods: public anywhere, protected in class hierarchy, private to declaring class only.
Example code
```
<?php
class A { public $x; protected $y; private $z; }
```
Question 9
static in PHP?
Static properties/methods belong to the class, not instances. Late static binding uses static:: for overridden static calls.
Example code
```
<?php
class B { public static $n = 0; }
```
Question 10
What are traits?
Horizontal code reuse; compose behavior into classes when multiple inheritance isn't available.
Example code
```
<?php
trait T { function hi() { echo "hi"; } }
class C { use T; }
```
Question 11
Abstract class vs interface?
Abstract class can hold state and partial implementation; interface is a pure contract. A class extends one abstract, implements many interfaces.
Example code
```
<?php
interface I { public function m(): void; }
```
Question 12
What is PDO?
Database abstraction layer with prepared statements; safer than raw concatenation for SQL injection prevention.
Example code
```
<?php
$pdo = new PDO("sqlite::memory:");
$st = $pdo->prepare("SELECT ?");
$st->execute([1]);
```
Question 13
Prepared statements — why?
Separate SQL from data; database binds parameters, blocking most injection and aiding query plan reuse.
Example code
```
<?php
$st = $pdo->prepare("SELECT * FROM u WHERE id = :id");
$st->execute([":id" => $id]);
```
Question 14
What is mysqli?
MySQL-specific extension; can be procedural or OOP. PDO is preferred when supporting multiple DB vendors.
Example code
```
<?php
$mysqli = new mysqli("127.0.0.1", "u", "p", "db");
```
Question 15
Sessions in PHP?
session_start() ties a cookie (PHPSESSID) to server-side storage; $_SESSION persists per user across requests.
Example code
```
<?php
session_start();
$_SESSION["uid"] = 1;
```
Question 16
Cookies vs sessions?
Cookies are client-stored small data; sessions store sensitive data server-side with only an ID in the cookie.
Example code
```
<?php
setcookie("theme", "dark", ["httponly" => true, "samesite" => "Lax"]);
```
Question 17
What is htmlspecialchars?
Escapes HTML special chars for output context—essential when echoing user input to prevent XSS.
Example code
```
<?php
echo htmlspecialchars($userInput, ENT_QUOTES, "UTF-8");
```
Question 18
filter_var and validation?
Built-in filters validate/sanitize emails, URLs, ints—first line of defense before business rules.
Example code
```
<?php
$email = filter_var($s, FILTER_VALIDATE_EMAIL);
```
Question 19
What is OPcache?
Bytecode cache in production PHP; avoids re-parsing on every request—huge win for throughput.
Example code
```
<?php
// opcache.enable=1 in php.ini for production
```
Question 20
PHP-FPM?
FastCGI Process Manager runs PHP workers behind nginx/Apache; pools, workers, and timeouts tune concurrency.
Example code
```
<?php
// php-fpm pool pm.max_children tuning
```
Question 21
What is Laravel?
Popular MVC framework: routing, Eloquent ORM, Blade, queues, scheduling—batteries included for web apps.
Example code
```
<?php
// routes/web.php Route::get("/", fn() => view("home"));
```
Question 22
Eloquent ORM basics?
Active-record style models; relationships (hasMany, belongsTo), migrations, and query builder fluent API.
Example code
```
<?php
// User::with("posts")->get();
```
Question 23
Blade templates?
Compiled to plain PHP; @if, @foreach, layouts/components—escape with {{ }} by default.
Example code
```
<?php
// @foreach($items as $i) {{ $i->name }} @endforeach
```
Question 24
What is middleware?
HTTP pipeline layers that inspect/modify request/response (auth, logging) before the controller.
Example code
```
<?php
// $stack->push(new AuthMiddleware());
```
Question 25
What is Symfony?
Component-based framework and full stack; HttpFoundation, DependencyInjection, used standalone or in Laravel pieces.
Example code
```
<?php
// $container->bind(I::class, Impl::class);
```
Question 26
Dependency injection in PHP?
Constructor injection of services/interfaces; containers (Laravel/Symfony) resolve concrete implementations.
Example code
```
<?php
use Psr\Http\Message\ServerRequestInterface;
```
Question 27
What is PSR-7?
HTTP message interfaces (Request/Response) enabling interoperable middleware and clients.
Example code
```
<?php
// composer dump-autoload -o
```
Question 28
What is PSR-4?
Autoloading standard mapping namespaces to directory structures—Composer's default.
Example code
```
<?php
try { throw new Exception("x"); } catch (Exception $e) { echo $e->getMessage(); }
```
Question 29
Error vs Exception in PHP?
Throwable base; Error for engine/type issues, Exception for catchable app errors. try/catch/finally handle Exceptions; errors differ by version/handler.
Example code
```
<?php
function f(int $x): string { return (string)$x; }
```
Question 30
Type declarations?
Scalar and return types (PHP 7+), union types, nullable ?, readonly properties (8.1+), enums (8.1)—modern PHP is strongly typed optionally.
Example code
```
<?php
$a = null;
echo $a ?? "default";
```
Question 31
What is null coalescing ??
Returns left if set and not null, else right—cleaner than isset ternary chains.
Example code
```
<?php
usort($a, fn($x, $y) => $x <=> $y);
```
Question 32
What is the spaceship operator <=>?
Three-way compare returning -1, 0, 1—handy for usort callbacks.
Example code
```
<?php
function gen() { yield 1; yield 2; }
foreach (gen() as $v) echo $v;
```
Question 33
Generators yield?
Memory-efficient iterators; yield produces values lazily instead of building huge arrays.
Example code
```
<?php
declare(strict_types=1);
function add(int $a, int $b): int { return $a + $b; }
```
Question 34
What is declare(strict_types=1)?
Enforces strict scalar typing per file—arguments and returns won't coerce unexpectedly.
Example code
```
<?php
// escape output; Content-Security-Policy header
```
Question 35
What is XSS in PHP apps?
Injected markup/script in output; mitigate with escaping, CSP, and avoiding raw echo of user data.
Example code
```
<?php
// @csrf in Blade / session token in forms
```
Question 36
CSRF protection?
Synchronizer token in forms or SameSite cookies; frameworks provide middleware/helpers.
Example code
```
<?php
echo password_hash("secret", PASSWORD_DEFAULT);
```
Question 37
Password hashing?
password_hash(PASSWORD_DEFAULT) and password_verify—never store plaintext or use weak hashes.
Example code
```
<?php
// move_uploaded_file($_FILES["f"]["tmp_name"], $safePath);
```
Question 38
File uploads safely?
Check type/size, store outside webroot or serve via script, randomize filenames, scan if needed.
Example code
```
<?php
print_r(array_map(fn($x) => $x * 2, [1, 2, 3]));
```
Question 39
What is Array functions (PHP context)?
array_map/filter/reduce, array_merge, array_key_exists—know big-O and copies vs references in large data.
Example code
```
<?php
$q = new SplQueue();
$q->enqueue(1);
echo $q->dequeue();
```
Question 40
What is SPL (PHP context)?
Standard PHP Library: iterators, exceptions, data structures—SplQueue, SplStack for structured collections.
Example code
```
<?php
// php composer.phar install
```
Question 41
What is Phar (PHP context)?
PHP archives packaging apps; used for tools like Composer phar distribution.
Example code
```
<?php
// pcov for coverage; xdebug.mode=debug
```
Question 42
What is PCOV vs Xdebug (PHP context)?
Lightweight coverage (PCOV) vs full debugger/profiler (Xdebug)—tradeoffs in CI and local dev.
Example code
```
<?php
// ./vendor/bin/phpunit
```
Question 43
What is PHPUnit basics (PHP context)?
Unit tests with assertions, data providers, mocks; run in CI on every push.
Example code
```
<?php
// vendor/bin/phpstan analyse src
```
Question 44
What is PHPStan/Psalm (PHP context)?
Static analysis finds bugs without running code; levels gradually increase strictness.
Example code
```
<?php
// vendor/bin/rector process src
```
Question 45
What is Rector (PHP context)?
Automated refactoring across PHP versions—helps upgrades 7→8.
Example code
```
<?php
// dispatch(new SendEmail($u));
```
Question 46
What is Laravel queues (PHP context)?
Defer slow work to workers (Redis/DB); failed_jobs table and retries for resilience.
Example code
```
<?php
// event(new OrderShipped($order));
```
Question 47
What is Laravel events (PHP context)?
Decouple domains: fire events, listen synchronously or via queue.
Example code
```
<?php
// Route::get("/users/{user}", fn(User $user) => $user);
```
Question 48
What is Route model binding (PHP context)?
Inject models by ID in routes; implicit or explicit resolution in controllers.
Example code
```
<?php
// $kernel = new Kernel($env, $debug);
// $response = $kernel->handle($request);
```
Question 49
What is Symfony kernel (PHP context)?
HttpKernel handles request lifecycle; EventDispatcher hooks many extension points.
Example code
```
<?php
// $em->persist($entity); $em->flush();
```
Question 50
What is Doctrine ORM (PHP context)?
Data mapper style in Symfony ecosystem; entities, UnitOfWork, DQL vs native SQL tradeoffs.
Example code
```
<?php
// while (have_posts()) { the_post(); the_title(); }
```
Question 51
What is WordPress (PHP context)?
Loop, hooks (actions/filters), wpdb—different from MVC frameworks; security around plugins/themes matters.
Example code
```
<?php
// \Drupal::entityTypeManager()->getStorage("node");
```
Question 52
What is Drupal (PHP context)?
Content entities, hooks, Symfony components underneath in modern versions.
Example code
```
<?php
// $om = \Magento\Framework\App\ObjectManager::getInstance();
```
Question 53
What is Magento (PHP context)?
E-commerce platform; heavy DI XML, plugins (interceptors), performance and caching critical.
Example code
```
<?php
// opcache.jit=tracing in php.ini
```
Question 54
What is OPcache JIT (PHP context)?
PHP 8 JIT can speed numeric tight loops; impact varies—profile before relying on it.
Example code
```
<?php
$fiber = new Fiber(fn() => Fiber::suspend("a"));
$fiber->start();
```
Question 55
What is Fibers (PHP context)?
PHP 8.1 fibers enable cooperative multitasking; async libraries may build atop them.
Example code
```
<?php
#[\Attribute]
class Route { public function __construct(public string $path) {} }
```
Question 56
What is Attributes (PHP context)?
PHP 8 metadata on classes/methods replacing docblock annotations in frameworks.
Example code
```
<?php
readonly class Point { public function __construct(public int $x, public int $y) {} }
```
Question 57
What is Readonly class (PHP context)?
PHP 8.2 readonly classes freeze all properties after construction—immutable DTO pattern.
Example code
```
<?php
function login(#[\SensitiveParameter] string $pw) {}
login("x");
```
Question 58
What is SensitiveParameter (PHP context)?
Attribute to redact secrets in stack traces (PHP 8.2).
Example code
```
<?php
enum S: string { case On = "on"; }
echo S::On->value;
```
Question 59
What is enum backed (PHP context)?
Backed enums serialize to scalar values; match() exhaustiveness helps switches.
Example code
```
<?php
echo match (3) { 1 => "a", 2, 3 => "b", default => "z" };
```
Question 60
What is match vs switch (PHP context)?
match is expression, strict compares, no fall-through—safer than switch for many cases.
Example code
```
<?php
$d = array_map(fn($x) => $x + 1, [1, 2]);
```
Question 61
What is Arrow functions fn (PHP context)?
Short closures capturing outer variables by value automatically (PHP 7.4).
Example code
```
<?php
$a = [1, ...[2, 3]];
```
Question 62
What is Spread in arrays (PHP context)?
[...$a] copies with integer keys reindexed; beware string keys behavior.
Example code
```
<?php
echo $user?->profile?->name;
```
Question 63
What is Nullsafe operator (PHP context)?
?-> chains calls/properties; stops at first null like JS optional chaining.
Example code
```
<?php
strlen(string: "hi");
```
Question 64
What is Named arguments (PHP context)?
Call functions with parameter names for clarity and skipping defaults (PHP 8).
Example code
```
<?php
class P { function __construct(public int $x) {} }
```
Question 65
What is Constructor promotion (PHP context)?
Combine property declaration and assignment in constructor parameters (PHP 8).
Example code
```
<?php
function id(int|string $v): int|string { return $v; }
```
Question 66
What is Union types (PHP context)?
string|int style declarations for parameters and returns.
Example code
```
<?php
function dumpJson(mixed $d): string { return json_encode($d); }
```
Question 67
What is Mixed type (PHP context)?
Explicit top type when anything is accepted—prefer narrowing inside function.
Example code
```
<?php
function fail(): never { throw new Exception(); }
```
Question 68
What is Never return type (PHP context)?
Function always exits (throw/exit) or loops forever—helps static analysis.
Example code
```
<?php
$wm = new WeakMap();
$o = new stdClass();
$wm[$o] = 1;
```
Question 69
What is WeakMap in PHP (PHP context)?
Keys are objects; entries disappear when object is GC'd—similar idea to JS WeakMap.
Example code
```
<?php
$cl = function () { return $this->x; };
$cl = $cl->bindTo((object)["x"=>1], null);
```
Question 70
What is Closure bindTo (PHP context)?
Change $this and scope of a closure—advanced meta-programming.
Example code
```
<?php
$r = new ReflectionClass(DateTime::class);
echo $r->getName();
```
Question 71
What is Reflection API (PHP context)?
Inspect classes at runtime; used in containers, serializers, tests—has a performance cost.
Example code
```
<?php
// prefer __serialize/__unserialize (PHP 7.4+)
```
Question 72
What is Serializable interface (PHP context)?
Legacy custom serialization; __serialize/__unserialize preferred in modern PHP.
Example code
```
<?php
class Action { function __invoke() { return 1; } }
echo (new Action())();
```
Question 73
What is __invoke (PHP context)?
Make an object callable as a function—single-action classes and Laravel invokable controllers.
Example code
```
<?php
class M { function __get($n) { return 1; } }
echo (new M())->a;
```
Question 74
What is Magic methods (PHP context)?
__get, __set, __call—convenient but can hide errors and hurt static analysis.
Example code
```
<?php
class C implements IteratorAggregate { function getIterator(): Traversable { yield 1; } }
```
Question 75
What is IteratorAggregate (PHP context)?
Implement getIterator() to make objects foreach-able cleanly.
Example code
```
<?php
class Bag implements Countable { function count(): int { return 3; } }
```
Question 76
What is Countable interface (PHP context)?
Implement count() for custom collections.
Example code
```
<?php
class A implements ArrayAccess { function offsetExists($o): bool { return true; } /* ... */ }
```
Question 77
What is ArrayAccess (PHP context)?
Object behaves like array with offset access—use sparingly for clarity.
Example code
```
<?php
// $client = new \GuzzleHttp\Client();
// $client->get("https://api");
```
Question 78
What is Guzzle HTTP (PHP context)?
Popular PSR-7 client; async pools, middleware, retries in ecosystem packages.
Example code
```
<?php
// $log = new Logger("app"); $log->pushHandler(new StreamHandler("php://stderr"));
```
Question 79
What is Monolog (PHP context)?
Structured logging handlers (stream, syslog, Slack); channels and processors.
Example code
```
<?php
// echo Carbon::now()->addDays(1);
```
Question 80
What is Carbon (PHP context)?
DateTime wrapper for parsing/formatting/diff common in Laravel.
Example code
```
<?php
// $redis = new Redis(); $redis->connect("127.0.0.1");
```
Question 81
What is Redis in PHP (PHP context)?
Caching, sessions, queues; connection pooling and serialization format choices matter.
Example code
```
<?php
// $m = new Memcached(); $m->addServer("127.0.0.1", 11211);
```
Question 82
What is Memcached (PHP context)?
Distributed memory cache; compare persistence and features vs Redis for your workload.
Example code
```
<?php
// $s3->putObject([...]);
```
Question 83
What is S3 uploads (PHP context)?
Presigned URLs or server-side SDK; never expose long-lived credentials in browser.
Example code
```
<?php
// Redis INCR + EXPIRE token bucket
```
Question 84
What is Rate limiting (PHP context)?
Throttle by IP/user; token bucket in Redis common for APIs.
Example code
```
<?php
header("Access-Control-Allow-Origin: https://app.example");
```
Question 85
What is CORS in PHP APIs (PHP context)?
Send Access-Control-* headers from backend; preflight OPTIONS for non-simple requests.
Example code
```
<?php
$o = json_decode('{"a":1}', true, 512, JSON_THROW_ON_ERROR);
```
Question 86
What is JSON (PHP context)?
json_encode/decode; JSON_THROW_ON_ERROR flag avoids silent failures.
Example code
```
<?php
$xml = simplexml_load_string("<r/>");
```
Question 87
What is XML parsing (PHP context)?
SimpleXML vs DOMDocument; XXE risks—disable external entities when parsing untrusted XML.
Example code
```
<?php
preg_match("/^\d+$/", "123", $m);
```
Question 88
What is Regular expressions (PHP context)?
preg_match_all, PCRE modifiers; ReDoS risk with user patterns.
Example code
```
<?php
$body = stream_get_contents(fopen("php://input", "r"));
```
Question 89
What is Streams (PHP context)?
php://input, fopen wrappers; handle large files without loading all into memory.
Example code
```
<?php
// cycles collected automatically
```
Question 90
What is Garbage collection (PHP context)?
Cycles collected; long-running workers may need gc_collect_cycles awareness.
Example code
```
<?php
// ini_set("memory_limit", "256M");
```
Question 91
What is Memory limits (PHP context)?
ini memory_limit; batch processing should chunk to avoid OOM in CLI/cron.
Example code
```
<?php
// php -d opcache.opt_debug_level=0x10000 script.php
```
Question 92
What is Opcodes (PHP context)?
Understanding vld/opcache output is niche but shows how PHP executes bytecode.
Example code
```
<?php
// long-lived workers; reset state per request
```
Question 93
What is FrankenPHP / RoadRunner (PHP context)?
Long-lived PHP workers with shared bootstrap—different from classic FPM per-request model.
Example code
```
<?php
apcu_store("k", 1, 60);
echo apcu_fetch("k");
```
Question 94
What is APCu cache (PHP context)?
In-process user cache for serialized values—faster than remote cache for local lookups.
Example code
```
<?php
// php artisan horizon
```
Question 95
What is Laravel Horizon (PHP context)?
Dashboard and metrics for Redis queues; auto-scaling workers in some deployments.
Example code
```
<?php
// $bus->dispatch(new MyMessage());
```
Question 96
What is Symfony Messenger (PHP context)?
Message bus with transports (sync, AMQP, Redis) for async command handling.
Example code
```
<?php
// ApiResource attribute on entity
```
Question 97
What is API Platform (PHP context)?
JSON-LD/OpenAPI from entities; rapid API scaffolding on Symfony components.
Example code
```
<?php
// $user->createToken("device")->plainTextToken
```
Question 98
What is Laravel Sanctum (PHP context)?
SPA/API token auth lightweight alternative to Passport for first-party apps.
Example code
```
<?php
echo getenv("APP_ENV");
```
Question 99
What is Env vars in PHP (PHP context)?
vlucas/phpdotenv loads .env; never commit secrets; production should use real env injection.
Example code
```
<?php
// FROM php:8.3-fpm
```
Question 100
What is Docker PHP images (PHP context)?
Official images variants (apache, fpm, cli); match extensions via docker-php-ext-install.
Example code
```
<?php
// Route::get("/health", fn() => response()->json(["ok" => true]));
```
Question 101
What is Health checks (PHP context)?
Expose /health for load balancers; check DB/Redis connectivity without heavy side effects.
Example code
```
<?php
// php artisan octane:start
```
Question 102
What is Laravel Octane (PHP context)?
Swoole/RoadRunner-powered app server for Laravel—persistent workers reduce bootstrap cost per request.
Example code
```
// php — add snippet 102
```

What is PHP?

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

What are PHP superglobals?

include vs require?

What is autoloading?

What is Composer?

What is a namespace?

public, protected, private?

static in PHP?

What are traits?

Abstract class vs interface?

What is PDO?

Prepared statements — why?

What is mysqli?

Sessions in PHP?

Cookies vs sessions?

What is htmlspecialchars?

filter_var and validation?

What is OPcache?

PHP-FPM?

What is Laravel?

Eloquent ORM basics?

Blade templates?

What is middleware?

What is Symfony?

Dependency injection in PHP?

What is PSR-7?

What is PSR-4?

Error vs Exception in PHP?

Type declarations?

What is null coalescing ??

What is the spaceship operator <=>?

Generators yield?

What is declare(strict_types=1)?

What is XSS in PHP apps?

CSRF protection?

Password hashing?

File uploads safely?

What is Array functions (PHP context)?

What is SPL (PHP context)?

What is Phar (PHP context)?

What is PCOV vs Xdebug (PHP context)?

What is PHPUnit basics (PHP context)?

What is PHPStan/Psalm (PHP context)?

What is Rector (PHP context)?

What is Laravel queues (PHP context)?

What is Laravel events (PHP context)?

What is Route model binding (PHP context)?

What is Symfony kernel (PHP context)?

What is Doctrine ORM (PHP context)?

What is WordPress (PHP context)?

What is Drupal (PHP context)?

What is Magento (PHP context)?

What is OPcache JIT (PHP context)?

What is Fibers (PHP context)?

What is Attributes (PHP context)?

What is Readonly class (PHP context)?

What is SensitiveParameter (PHP context)?

What is enum backed (PHP context)?

What is match vs switch (PHP context)?

What is Arrow functions fn (PHP context)?

What is Spread in arrays (PHP context)?

What is Nullsafe operator (PHP context)?

What is Named arguments (PHP context)?

What is Constructor promotion (PHP context)?

What is Union types (PHP context)?

What is Mixed type (PHP context)?

What is Never return type (PHP context)?

What is WeakMap in PHP (PHP context)?

What is Closure bindTo (PHP context)?

What is Reflection API (PHP context)?

What is Serializable interface (PHP context)?

What is __invoke (PHP context)?

What is Magic methods (PHP context)?

What is IteratorAggregate (PHP context)?

What is Countable interface (PHP context)?

What is ArrayAccess (PHP context)?

What is Guzzle HTTP (PHP context)?

What is Monolog (PHP context)?

What is Carbon (PHP context)?