Prepare for your next PHP developer interview with our comprehensive list of frequently asked questions and expert answers. Whether you’re a fresher or an experienced professional, these questions cover the fundamentals, best practices, and advanced concepts to help you succeed.
Here’s a list of the frequently asked data science questions with answers on the technical concept which you can expect to face during an interview.
PHP stands for “php: Hypertext Preprocessor”. it is a server-side scripting language designed for web development but also used as a general-purpose programming language.
PHP code is enclosed within special begin and stop processing instructions:
<?php
// PHP code here
?>
Both are used to output data, but echo is slightly faster and can take multiple parameters. Print always returns 1 and can only take a single argument.
| Feature | echo | print |
| Return Value | Does not return any value. | Returns 1, allowing it to be used in expressions. |
| Speed | Slightly faster as it does not return a value. | Slightly slower due to the return value. |
| Usage | Can output one or more strings, separated by commas. | Outputs a single string only. |
| Parentheses | Parentheses are optional. | Parentheses are optional, but print is always a single argument function. |
| Example | echo "Hello, ", "world!" | print "Hello, world!" |
php
echo "Hello", " ", "World"; // Valid
print("Hello World"); // Valid
print "Hello", "World"; // Invalid
PHP has three main types of errors:
PHP supports the following data types:
`==` checks for equality of value, while `===` checks for both equality of value and type.
php
$a = 5;
$b = "5";
var_dump($a == $b); // bool(true)
var_dump($a === $b); // bool(false)
Type juggling (or type coercion) is automatic type conversion of values when an operator is used with different types.
php
$foo = "1"; // $foo is string (ASCII 49)
$foo *= 2; // $foo is now an integer (2)
$foo = $foo * 1.3; // $foo is now a float (2.6)
`$arr[]` is slightly faster for adding a single element. `array_push()` can add multiple elements and is more readable.
php
$arr[] = 1; // Faster for single element
array_push($arr, 2, 3, 4); // Can add multiple elements
Use the `array_unique()` function:
php
$array = array(1, 2, 2, 3, 4, 4, 5);
$unique_array = array_unique($array);
print_r($unique_array);
`str_replace()` is case-sensitive, while `str_ireplace()` is case-insensitive.
str_replace() and str_ireplace() in PHP| Feature | str_replace() | str_ireplace() |
| Case Sensitivity | Case-sensitive string replacement. | Case-insensitive string replacement. |
| Use Case | Used when case sensitivity matters in replacing substrings. | Used when case sensitivity does not matter in replacing substrings. |
| Functionality | Replaces all occurrences of a string, respecting case. | Replaces all occurrences of a string, ignoring case. |
| Example | str_replace("Hello", "Hi", "Hello World"); | str_ireplace("hello", "Hi", "Hello World"); |
Use sort() for ascending and rsort() for descending order:
phpCopy$numbers = [3, 1, 4, 1, 5, 9];
sort($numbers); // Ascending
print_r($numbers);
rsort($numbers); // Descending
print_r($numbers);
Use the `array_merge()` function:
php
$array1 = [1, 2, 3];
$array2 = [4, 5, 6];
$merged = array_merge($array1, $array2);
print_r($merged); // Outputs: Array ( [0] => 1 [1] => 2 [2] => 3 [3] => 4 [4] => 5 [5] => 6 )
Use the `strpos()` function:
php
$str = "Hello,World";
print_r(explode(",", $str)); // Array ( [0] => Hello [1] => World )
print_r(str_split($str, 3)); // Array ( [0] => Hel [1] => lo, [2] => Wor [3] => ld )
Use the `strpos()` function:
php
$haystack = "The quick brown fox";
$needle = "quick";
if (strpos($haystack, $needle) !== false) {
echo "The string contains 'quick'";
}
The main principles of OOP are:
1. Encapsulation
2. Inheritance
3. Polymorphism
4. Abstraction
An abstract class can have both abstract and non-abstract methods, while an interface can only have abstract methods. A class can implement multiple interfaces but extend only one abstract class.
A class is a blueprint or template for creating objects. It defines the properties (attributes) and methods (functions) that the objects of that class will have.
php
class Car {
public $color;
public $brand;
public function startEngine() {
echo "The car is starting!";
}
}
An object is an instance of a class. It’s a concrete entity based on the class blueprint, with its own set of property values.
php
$myCar = new Car();
$myCar->color = "red";
$myCar->brand = "Toyota";
$myCar->startEngine(); // Outputs: The car is starting!
A constructor is a special method in a class that is automatically called when an object of that class is created. It’s used to initialize the object’s properties.
php
class Person {
public $name;
public $age;
public function __construct($name, $age) {
$this->name = $name;
$this->age = $age;
}
}
$person = new Person("John", 30);
echo $person->name; // Outputs: John
Inheritance is a mechanism where a new class is derived from an existing class. The new class (child) inherits properties and methods from the existing class (parent).
php
class Animal {
public function eat() {
echo "This animal eats food.";
}
}
class Dog extends Animal {
public function bark() {
echo "Woof!";
}
}
$dog = new Dog();
$dog->eat(); // Outputs: This animal eats food.
$dog->bark(); // Outputs: Woof!
Access modifiers are keywords that define the visibility and accessibility of class properties and methods. In PHP, there are three access modifiers:
– public: accessible from anywhere
– protected: accessible within the class and its child classes
– private: accessible only within the class itself
php
class Example {
public $public = "Public";
protected $protected = "Protected";
private $private = "Private";
public function testAccess() {
echo $this->public; // Works
echo $this->protected; // Works
echo $this->private; // Works
}
}
$obj = new Example();
echo $obj->public; // Works
echo $obj->protected; // Fatal Error
echo $obj->private; // Fatal Error
Polymorphism allows objects of different classes to be treated as objects of a common base class. In PHP, it can be implemented through inheritance and interfaces.
php
interface Shape {
public function area();
}
class Circle implements Shape {
private $radius;
public function __construct($radius) {
$this->radius = $radius;
}
public function area() {
return pi() * $this->radius ** 2;
}
}
class Rectangle implements Shape {
private $width, $height;
public function __construct($width, $height) {
$this->width = $width;
$this->height = $height;
}
public function area() {
return $this->width * $this->height;
}
}
function printArea(Shape $shape) {
echo "Area: " . $shape->area() . "\n";
}
$circle = new Circle(5);
$rectangle = new Rectangle(4, 6);
printArea($circle); // Outputs: Area: 78.539816339745
printArea($rectangle); // Outputs: Area: 24
Use functions like `htmlspecialchars()`, `strip_tags()`, or `filter_var()`:
php
$clean_input = htmlspecialchars($user_input, ENT_QUOTES, 'UTF-8');
XSS is a security vulnerability that allows attackers to inject client-side scripts into web pages. Prevent it by sanitising user input and using Content Security Policy (CSP).
`password_hash()` creates a secure hash of passwords, automatically applying salt and using a strong algorithm:
php
$hashed_password = password_hash($password, PASSWORD_DEFAULT);
Some ways to optimize PHP performance include:
– Use a PHP accelerator (e.g., OPcache)
– Minimize database queries
– Use caching mechanisms
– Avoid using `@` to suppress errors
– Use single quotes for strings without variables
`include` and `require` behave similarly, but `require` produces a fatal error if the file is not found. The `_once` variants ensure the file is included only once.
Popular PHP frameworks include:
– Laravel
– Symfony
– CodeIgniter
– Yii
– Zend Framework
– CakePHP
Composer is a dependency management tool for PHP. It allows you to declare the libraries your project depends on and manages them for you.
PHPUnit is a unit testing framework for PHP. It provides an ecosystem for writing and running tests to ensure code quality and catch bugs early.
Generators provide an easy way to implement simple iterators without the overhead or complexity of implementing a class that implements the Iterator interface.
php
function countTo10() {
for ($i = 1; $i <= 10; $i++) {
yield $i;
}
}
foreach (countTo10() as $number) {
echo "$number ";
}
`__construct()` is called when an object is created and is used for initialization. `__destruct()` is called when an object is destroyed and is used for cleanup.
Magic methods are special methods that override PHP’s default action when certain actions are performed on an object. Examples include `__get()`, `__set()`, `__call()`, and `__toString()`.
The `static` keyword is used to declare properties and methods that can be accessed without instantiating the class.
php
class Counter {
public static $count = 0;
public static function increment() {
self::$count++;
}
}
Counter::increment();
echo Counter::$count; // Outputs: 1
`self` refers to the class where it’s used, while `static` refers to the called class in inheritance scenarios (late static binding).
Namespaces are a way of encapsulating items to avoid name conflicts. They’re especially useful for better organizing and grouping related classes.
php
namespace MyProject\Utils;
class StringHelper {
// ...
}
PHP uses a try-catch block for exception handling:
php
try {
// Code that may throw an exception
throw new Exception("Error message");
} catch (Exception $e) {
echo "Caught exception: " . $e->getMessage();
} finally {
// This block always executes
}
`GET` sends data as part of the URL, while `POST` sends data in the request body. `GET` is less secure and has length limitations, while `POST` can send larger amounts of data more securely.
GET and POST Methods in PHP| Feature | GET Method | POST Method |
| Data Visibility | Data is visible in the URL. | Data is not visible in the URL. |
| Data Size Limit | Limited to a maximum of 2048 characters. | No size limit (limited by server settings). |
| Use Case | Used for retrieving data. | Used for sending data, such as form submissions. |
| Caching | Data can be cached. | Data is not cached. |
| Bookmarking | Can be bookmarked. | Cannot be bookmarked. |
| Security | Less secure as data is exposed in the URL. | More secure as data is not exposed in the URL. |
The `final` keyword prevents child classes from overriding a method or prevents a class from being inherited.
php
final class CannotBeInherited {
// ...
}
class NormalClass {
final public function cannotBeOverridden() {
// ...
}
}
File uploads are handled using the `$_FILES` superglobal and the `move_uploaded_file()` function:
php
if ($_SERVER["REQUEST_METHOD"] == "POST") {
$uploadDir = '/uploads/';
$uploadFile = $uploadDir . basename($_FILES['userfile']['name']);
if (move_uploaded_file($_FILES['userfile']['tmp_name'], $uploadFile)) {
echo "File is valid, and was successfully uploaded.";
} else {
echo "Upload failed.";
}
}
session_start()` creates a new session or resumes an existing one, while `session_destroy()` destroys all data associated with the current session.
session_start() and session_destroy() in PHP| Feature | session_start() | session_destroy() |
| Purpose | Starts or resumes an existing session. | Ends a session and deletes all session data. |
| Usage | Called at the beginning of a script to access or create session variables. | Called when you want to end the session and clear session data. |
| Effect on Session Variables | Accesses or initializes session variables. | Removes all session variables. |
| Session Continuity | Keeps the session active. | Terminates the session. |
| Session ID | Retains the session ID. | Destroys the session data but does not delete the session cookie by default. |
By mastering the PHP interview questions and answers presented in this guide, you’ll be well-prepared to demonstrate your proficiency and secure your next PHP developer role. These questions cover essential concepts and practical knowledge that will help you stand out in interviews.
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