Mastering the PHP Developer Interview: 100+ Technical Questions Answered. 46-60.

Mastering the PHP Developer Interview: 100+ Technical Questions Answered. 46-60.


20 min read

In this segment, we delve into vital PHP concepts to sharpen your interview skills. From understanding Docker's workings to deciphering the SSH protocol, and from exploring the power of PDO to distinguishing between GET and POST, we provide clear insights.

Learn the nuances between single and double quotes, the significance of Cookies, and their limitations.

Grasp the essence of PSR standards and the role of Composer in PHP. Understand PHPStan's importance and unravel the differences between require and require-dev in Composer.

Gain clarity on versioning and the role of composer.json versus composer.lock.

Lastly, uncover additional features of the PHP interpreter and explore methods to modify private properties of a class.

46. What is Docker? How does it work?


Imagine Docker as a set of identical lunch boxes, each containing a meal. Docker allows you to package an application and all its dependencies into a standardized container, making it easy to move and run the application consistently across different environments.

Principle of Docker:

  1. Containerization:

    • Like lunch boxes that hold meals, Docker containers hold applications.

    • Containers package everything needed to run an application, including code, libraries, and settings.

  2. Image:

    • Like a recipe for a meal, a Docker image is a blueprint for a container.

    • Images are created from a set of instructions defined in a Dockerfile.

  3. Dockerfile:

    • Like a cooking recipe, a Dockerfile defines the steps to create an image.

    • It includes instructions to install dependencies, copy files, and configure settings.

  4. Registry:

    • Like a cafeteria with labeled lunch boxes, a Docker registry stores images.

    • Docker Hub is a popular public registry, and you can create private registries too.

  5. Containerization Benefits:

    • Consistency: Applications run the same way across different environments.

    • Isolation: Containers are isolated from each other, preventing conflicts.

    • Portability: You can move containers between different systems seamlessly.

    • Resource Efficiency: Containers share the host OS, saving resources compared to virtual machines.

  6. Docker Engine:

    • Like a lunch delivery service, the Docker Engine manages containers.

    • It creates, runs, and stops containers based on images.

  7. Docker Compose:

    • Like planning a meal with multiple courses, Docker Compose defines and runs multi-container applications.

    • It uses a docker-compose.yml file to configure services, networks, and volumes.


Imagine you're a developer working on an application that requires specific libraries and settings. With Docker:

  1. You create a Dockerfile that includes the steps to install the required libraries.

  2. You build an image from the Dockerfile, creating a standardized container blueprint.

  3. You can run multiple containers from the same image on different systems, ensuring consistent behavior.

47. Tell me about the SSH protocol.

SSH (Secure Shell) Protocol:

Imagine SSH as a secure tunnel for sending secret messages. SSH is a network protocol that provides a secure way to access and manage remote devices and servers over an unsecured network, like the internet.

Principle of SSH:

  1. Encryption:

    • Like using a secret code to write a message, SSH encrypts data during communication.

    • Encryption ensures that sensitive information remains private and secure.

  2. Authentication:

    • Like showing an ID card to access a restricted area, SSH requires authentication.

    • Users need valid credentials (username and password or keys) to log in remotely.

  3. Key Pair:

    • Like having a lock and a key, SSH uses key pairs for authentication.

    • A public key (lock) is stored on the server, while the private key (key) is kept by the user.

  4. Public Key Authentication:

    • Like a secret handshake, public key authentication verifies the user's identity.

    • Users provide their private key, and the server checks if it matches the stored public key.

  5. Remote Command Execution:

    • Like sending a command to a remote robot, SSH allows users to execute commands on remote servers.

    • This is useful for managing servers without direct physical access.

  6. Secure File Transfer:

    • Like sending a confidential file through a secure courier, SSH provides SFTP (SSH File Transfer Protocol) for secure file transfers.

Benefits of SSH:

  • Security: Encryption ensures that data exchanged between client and server remains confidential.

  • Authentication: Only authorized users with valid credentials can access the server.

  • Data Integrity: Data remains unchanged during transmission, ensuring reliability.

  • Remote Access: SSH allows remote management of servers from anywhere.

  • Secure File Transfer: SFTP enables secure file sharing between devices.


Imagine you're a traveler accessing your home computer from a café:

  1. You initiate an SSH connection using your laptop (client) and your home computer (server).

  2. SSH uses encryption to secure your login credentials and commands you send.

  3. If you use public key authentication, your laptop's private key verifies your identity.

  4. You can run commands on your home computer as if you were physically there.

SSH ensures your connection and interactions are secure, preventing eavesdropping and unauthorized access. It's like having a secret passage to your remote devices over the internet.

48. What is PDO?

PDO (PHP Data Objects):

Imagine PDO as a versatile translator between different databases and your PHP code. PDO is a PHP extension that provides a consistent and efficient way to interact with databases, regardless of the specific database system being used.

Principle of PDO:

  1. Database Abstraction:

    • Like a multilingual tour guide, PDO abstracts the differences between database systems.

    • You write PHP code using PDO, and it handles the database-specific details.

  2. Supported Database Systems:

    • Like speaking different languages, PDO supports multiple database systems (MySQL, PostgreSQL, SQLite, etc.).

    • You can switch between databases without changing your code significantly.

  3. Prepared Statements:

    • Like writing a template and filling in the blanks, PDO uses prepared statements for querying databases.

    • Prepared statements help prevent SQL injection attacks and improve performance.

  4. Error Handling:

    • Like a translator explaining misunderstandings, PDO provides detailed error information.

    • You can handle errors more effectively and troubleshoot database interactions.

  5. Secure Data Access:

    • Like passing messages through a reliable courier, PDO ensures secure data transmission.

    • Data passed between PHP and the database is properly escaped and sanitized.

Benefits of PDO:

  • Database Agnostic: PDO supports various databases, reducing the need to rewrite code when changing databases.

  • Security: Prepared statements and proper data escaping help prevent SQL injection attacks.

  • Consistency: PDO provides a consistent API for different database systems.

  • Performance: Prepared statements are cached for faster execution.

  • Error Handling: Detailed error information helps in debugging and troubleshooting.


Imagine you're a librarian who speaks multiple languages and can translate books for visitors:

  1. You write PHP code using PDO to access a MySQL database.

  2. Later, you switch to a PostgreSQL database with minimal code changes thanks to PDO's database abstraction.

  3. You use prepared statements to insert user data into the database, preventing malicious SQL injection attempts.

Just like your role as a multilingual librarian, PDO plays the role of a reliable translator between PHP and various database systems, making database interactions smoother and more secure.

49. What is the difference between GET and POST?

Difference Between GET and POST:

Imagine you're sending a letter to a friend. Using GET and POST is like choosing different ways to send that letter.


  1. Method: Like sending a letter with the message written on the envelope.

  2. Visibility: The data is appended to the URL as query parameters.

  3. Security: Not suitable for sensitive data as it's visible in the URL.

  4. Caching: Data can be cached by browsers and servers.

  5. Length Limit: Limited by the maximum length of a URL.

  6. Use Cases: Used for retrieving data from the server, like fetching search results.


  1. Method: Like sending a sealed envelope with the message inside.

  2. Visibility: Data is sent in the request body, not visible in the URL.

  3. Security: Suitable for sensitive data as it's not visible in the URL.

  4. Caching: Data is not cached by browsers or servers.

  5. Length Limit: Limited by server settings and browser capabilities.

  6. Use Cases: Used for submitting data to the server, like submitting a form.

When to Use Which:

  • Use GET when you want to retrieve data from the server and when the data isn't sensitive or doesn't need to be hidden.

  • Use POST when you're sending data to the server, especially when dealing with sensitive information like passwords or when the data is too long for a URL.


Imagine you're ordering a pizza online:

  • GET: You use a link to view available pizza options (GET request).

  • POST: You fill out a form with your pizza choices and address, then submit it (POST request).

50. Is there a difference between single and double quotes?

Single Quotes (''):

  1. Literal Text: Like writing words exactly as they are.

  2. Escape Characters Ignored: Most escape characters (except for \\ and \') are treated as regular characters.

  3. No Variable Substitution: Variables inside single quotes are treated as text, not as their values.

  4. Faster: Processing single quotes is slightly faster as variable interpolation doesn't happen.

Double Quotes (""):

  1. Interpolation: Like filling in the blanks with actual words.

  2. Escape Characters Processed: Escape characters (e.g., \n, \t) are interpreted and replaced.

  3. Variable Substitution: Variables inside double quotes are replaced with their values.

  4. Slower: Processing double quotes is slightly slower due to variable interpolation.

51. What are Cookies, and why are they used?


Imagine cookies as small notes that a website leaves on your computer to remember things. Cookies are small pieces of data that websites store on a user's browser. They have various purposes, like remembering user preferences and tracking user interactions.

Purpose of Cookies:

  1. Session Management:

    • Like a wristband that identifies you at an event, cookies help maintain a session between a user and a website.

    • Cookies store session IDs to keep track of user interactions during a visit.

  2. Personalization:

    • Like a personalized welcome message, cookies remember user preferences and settings.

    • Websites can use cookies to customize the user experience based on past interactions.

  3. Tracking and Analytics:

    • Like collecting data on how many people attend an event, cookies track user behavior and interactions.

    • Websites use cookies to gather insights and improve their services.

  4. Authentication:

    • Like a VIP pass, cookies can help with user authentication after logging in.

    • They store login information or tokens to keep users logged in across different pages.

  5. Targeted Advertising:

    • Like showing ads relevant to your interests, cookies can track your browsing habits and show targeted ads.

Types of Cookies:

  1. Session Cookies:

    • Like temporary notes that are discarded after you leave an event, session cookies are stored temporarily and are removed when you close the browser.
  2. Persistent Cookies:

    • Like notes that you keep and refer to later, persistent cookies are stored on your device for a longer time.


Imagine you're attending a conference:

  • Session Cookie: You get a wristband with a unique code. The organizers use this code to identify you during the event, and it's discarded once the event ends.

  • Persistent Cookie: You receive a coupon that can be used for future discounts. You keep it and use it later.

52. What should not be stored in Cookies and why?

Cookies are not suitable for storing sensitive information due to security and privacy concerns.

Why Not to Store Sensitive Data:

  1. Security Risks:

    • Cookies are stored on the user's device, and they can be accessed by various parties, including hackers.
  2. Limited Storage:

    • Cookies have size limitations, and storing large amounts of data can cause performance issues.
  3. Lack of Encryption:

    • Cookies are usually transmitted over unencrypted connections, making sensitive data vulnerable during transmission.
  4. Data Breach Risk:

    • If a website's security is compromised, sensitive data stored in cookies can be exposed.

What to Do Instead:

  • Use secure methods like server-side sessions or tokens for handling sensitive data.

  • Encrypt and hash sensitive information before storing it anywhere.

53. What is PSR, and how is it used?

PSR (PHP-FIG Standard Recommendation):

Imagine PSR as a set of guidelines for developers, like a manual for building things that work well together. PSR is a set of standards created by the PHP Framework Interoperability Group (PHP-FIG) to ensure that PHP code is written in a consistent and interoperable manner.

PSR (PHP-FIG Standard Recommendation):

Imagine PSR as a set of guidelines for developers, like a manual for building things that work well together. PSR is a set of standards created by the PHP Framework Interoperability Group (PHP-FIG) to ensure that PHP code is written in a consistent and interoperable manner.

Usage of PSR:

  1. Autoloading (PSR-4):

    • Like having a library index, PSR-4 defines a standard for autoloading classes.

    • Instead of manually including files, you use autoloading to load classes automatically.

  2. Coding Style (PSR-1 and PSR-12):

    • Like following a common style guide, PSR-1 and PSR-12 define coding style standards.

    • These standards cover naming conventions, file structure, and code formatting.

  3. HTTP Message Interface (PSR-7):

    • Like using a universal language for communication, PSR-7 defines interfaces for HTTP messages.

    • This allows different libraries and frameworks to communicate seamlessly.

  4. Container Interface (PSR-11):

    • Like having a standardized container for ingredients, PSR-11 defines an interface for dependency injection containers.

    • Containers manage and provide objects to different parts of the application.

  5. Event Dispatcher (PSR-14):

    • Like having a schedule for events, PSR-14 defines interfaces for event dispatching.

    • This helps manage communication between different parts of an application.

Benefits of PSR:

  • Interoperability: Developers can use libraries and components from different sources that adhere to the same standards.

  • Consistency: Coding standards and interfaces make code more readable and maintainable.

  • Collaboration: Developers from various backgrounds can collaborate more effectively using common guidelines.

54. What is Composer?


Imagine Composer as a personal assistant for managing your software projects and their dependencies. Composer is a dependency management tool for PHP that simplifies the process of installing, updating, and managing external libraries and packages.

Purpose of Composer:

  1. Dependency Management:

    • Like keeping track of ingredients for a recipe, Composer manages dependencies required for your PHP projects.

    • It ensures that the right versions of libraries are used and avoids conflicts.

  2. Package Installation:

    • Like getting all the necessary tools for a project, Composer fetches and installs packages from various sources (like Packagist).
  3. Autoloading:

    • Like having a library catalog, Composer generates autoloader files that autoload classes when needed.
  4. Version Control:

    • Like keeping track of different versions of a document, Composer handles versioning of packages.

Usage of Composer:

  1. Creating a composer.json File:

    • Like making a shopping list, you create a composer.json file in your project directory.

    • This file lists the required packages and their versions.

    "require": {
        "monolog/monolog": "^2.0"
  1. Installing Packages:

    • Like going to the store and getting the items on your list, you run composer install in the terminal.

    • Composer fetches and installs the required packages according to your composer.json.

  2. Autoloading:

    • Like organizing your tools for easy access, Composer generates autoloader files based on your project's structure.
// Include the Composer autoloader
require 'vendor/autoload.php';
  1. Updating Packages:

    • Like upgrading your tools to newer models, you can update packages using composer update.

Benefits of Composer:

  • Efficiency: Composer automates dependency management, saving time and effort.

  • Consistency: All developers on a project use the same set of libraries and versions.

  • Maintenance: Keeping packages updated and organized becomes easier.

  • Compatibility: Composer ensures that dependencies work well together.


Imagine you're building a house, and you need various tools and materials:

  • Composer acts as a project manager, making sure you have the right tools (packages) for your project (house construction).

  • You specify the tools you need (dependencies) in your project plan (composer.json), and Composer gets them for you.

55. What is PHPStan?


Imagine PHPStan as a diligent code inspector that helps you find and fix mistakes in your PHP code. PHPStan is a static analysis tool for PHP that performs in-depth analysis of your code without actually executing it. It helps identify potential bugs, errors, and improvements in your codebase.

Purpose of PHPStan:

  1. Static Analysis:

    • Like reviewing a manuscript for grammar and spelling errors, PHPStan reviews your code for syntax, logic, and type-related issues.
  2. Bug Prevention:

    • Like proofreading to catch errors before publication, PHPStan helps catch bugs before they reach production.
  3. Code Quality:

    • Like having an editor suggest improvements in your writing, PHPStan suggests code improvements and adherence to best practices.

Usage of PHPStan:

  1. Installation:

    • Like installing a grammar checker for your writing, you install PHPStan using Composer.
composer require --dev phpstan/phpstan
  1. Configuration:

    • Like customizing grammar checker settings, you create a phpstan.neon configuration file in your project.
    level: 7
  1. Running Analysis:

    • Like running a grammar check on your document, you run PHPStan on your codebase.
vendor/bin/phpstan analyze

Benefits of PHPStan:

  • Error Prevention: PHPStan helps catch potential bugs early in the development process.

  • Code Quality: It enforces coding standards and suggests improvements for maintainable code.

  • Efficiency: Fixes are made during development, saving time and effort in the long run.

  • Documentation: PHPStan provides insights into types, methods, and more for better understanding.


Imagine you're writing a book, and you want to make sure it's error-free:

  • PHPStan acts like a grammar and style checker for your code.

  • It points out syntax errors, type mismatches, and potential issues, just like a grammar checker would do for a manuscript.

56. What's the difference between require and require-dev in Compose

Imagine you're building a house and need both essential tools and optional decorations. require and require-dev in Composer are similar to distinguishing between essential construction tools and optional items for aesthetic purposes.


  1. Essential Dependencies:

    • Like tools needed for basic construction, require lists packages required for the functionality of your application.

    • These packages are necessary for your application to work correctly.

  2. Production Use:

    • Like installing essential fixtures in a house, packages listed under require are necessary for your application to be operational in a production environment.
  3. Included in Distribution:

    • Like including basic house components, packages from require are installed when you distribute your application to users.


  1. Development Dependencies:

    • Like decorative items for the house, require-dev lists packages that are useful during development but not essential for the application's core functionality.

    • These packages include tools for testing, debugging, and code analysis.

  2. Development and Testing Use:

    • Like using specialized tools for construction planning, packages under require-dev are used during development, testing, and debugging phases.
  3. Excluded from Distribution:

    • Like leaving decorative items behind when selling a house, packages from require-dev are not installed when users download or install your application.


Imagine you're building a software application:

  • require is like listing the essential libraries your application needs to function properly.

  • require-dev is like listing tools, testing libraries, and development aids that enhance the development process but are not necessary for users who just want to use your application.

57. Explain versioning in Composer.

Versioning in Composer:

Imagine versioning in Composer as a way to ensure you're getting the right version of a product, like choosing a specific edition of a book. Versioning in Composer helps you define which version of a package or library your project should use.

Semantic Versioning (SemVer):

  1. Major Version (X.0.0):

    • Like a new edition of a book, a major version includes significant changes that might break compatibility with previous versions.
  2. Minor Version (X.Y.0):

    • Like updates to a book with new chapters, a minor version includes new features without breaking existing functionality.
  3. Patch Version (X.Y.Z):

    • Like fixing typos in a book, a patch version includes bug fixes and minor improvements without changing features.

Using Version Constraints:

  1. Exact Version (X.Y.Z):

    • Like asking for a specific book edition, you can request an exact version of a package.
"require": {
    "monolog/monolog": "1.0.0"
  1. Minimum Version (>=X.Y.Z):

    • Like asking for any book edition newer than a certain year, you can specify a minimum required version.
"require": {
    "monolog/monolog": ">=1.2.0"
  1. Compatible Versions (^X.Y.Z):

    • Like asking for any book edition in the same edition range, you can use the caret symbol to request compatible versions.
"require": {
    "monolog/monolog": "^1.3.0"

Version Constraints in Dependencies:

  1. Dependencies:

    • Like referencing books mentioned in the bibliography, your project's composer.json lists the packages your project depends on.
  2. Lock File:

    • Like confirming the availability of books in a library, Composer generates a composer.lock file to record exact versions of packages.


Imagine you're building a bookshelf:

  • You specify which edition of each book you want (package version).

  • If you only want books from a certain year (minimum version), you specify that.

  • If you're fine with any edition from a specific series (compatible versions), you indicate that preference.

58. What's the difference between composer.json and composer.lock?

Imagine you're planning a trip and you have both an itinerary (plan) and a confirmation of your bookings (receipts). composer.json is like your trip plan, outlining where you want to go and what you want to do. composer.lock is like your booking confirmation, providing exact details of what you've arranged.


  1. Project Plan:

    • Like creating a travel itinerary, composer.json is the file where you outline your project's dependencies and configuration.
  2. Dependency List:

    • Like listing the places you want to visit, composer.json lists the packages and libraries your project depends on.
  3. Version Constraints:

    • Like specifying when and where you want to travel, composer.json includes version constraints for each dependency.
  4. Editable:

    • Like adjusting your itinerary before the trip, you can modify composer.json to add, update, or remove dependencies.


  1. Exact Details:

    • Like having confirmed bookings, composer.lock contains the precise versions of each package that were installed when you last ran composer install.
  2. Dependency Versions:

    • Like having proof of your hotel reservation, composer.lock shows the exact package versions that were used in your project.
  3. Frozen State:

    • Like having your travel plans locked in, composer.lock ensures that everyone working on the project uses the same package versions.
  4. Generated Automatically:

    • Like receiving a booking confirmation, composer.lock is automatically generated when you run composer install or composer update.


  1. During Development:

    • Like using your itinerary to guide your travels, developers refer to composer.json while working on the project.
  2. Deployment and Collaboration:

    • Like presenting your booking confirmation while checking in, composer.lock is used to ensure consistent package versions when deploying or collaborating on a project.


Imagine you're organizing a group trip:

  • composer.json is like your travel plan, specifying destinations and activities.

  • composer.lock is like the confirmation email with booking details, ensuring everyone is on the same page about the trip arrangements.

59. What additional features does the PHP interpreter have?

Additional Features of the PHP Interpreter:

Imagine the PHP interpreter as a versatile tool that not only understands and executes your PHP code but also offers various useful features to enhance development and debugging.

Built-in Web Server:

  1. Development Server:

    • Like having a personal workspace, the PHP interpreter includes a built-in web server (php -S) for quickly testing PHP applications locally.
php -S localhost:8000

Interactive Mode:

  1. Command Line Interaction:

    • Like having a conversation with your code, PHP's interactive mode (php -a) lets you execute PHP statements directly in the command line.
php -a

Built-in Functions:

  1. Rich Functionality:

    • Like using specialized tools for specific tasks, PHP provides numerous built-in functions for tasks like string manipulation, array operations, date handling, and more.
$length = strlen("Hello, world!"); // String length

Error Reporting:

  1. Detailed Errors:

    • Like getting detailed feedback on a manuscript, PHP's error reporting provides information about issues in your code for easier debugging.

Profiling and Debugging:

Xdebug Integration: - Like using a magnifying glass to examine details, you can integrate Xdebug with PHP to step through your code, set breakpoints, and analyze performance.

Execution Modes:

  1. Standalone Scripts:

    • Like writing a standalone story, PHP can be used to create scripts that can be executed independently from a web server.


  1. Rich Ecosystem:

    • Like adding specialized tools to your toolbox, PHP supports a wide range of extensions for various tasks, like connecting to databases, working with images, and more.
// Example usage of a database extension
$pdo = new PDO("mysql:host=localhost;dbname=mydb", "username", "password");

CLI Options:

  1. Customization:

    • Like adjusting the settings in a text editor, PHP offers various command-line options (php -d, php -c) to customize its behavior.
php -d memory_limit=256M script.php

60. How can you modify a private property of a class?

Modifying Private Properties:

Imagine private properties of a class as the contents of a locked box. Only methods inside the class have the key to access and modify these properties. However, there are ways to modify private properties from within the class itself.

Using Setter Methods:

  1. Setter Methods:

    • Like providing a special opening mechanism for the locked box, you can create setter methods inside the class to modify private properties.
class MyClass {
    private $myProperty;

    public function setMyProperty($value) {
        $this->myProperty = $value;

$obj = new MyClass();
$obj->setMyProperty("New Value");

Direct Modification:

  1. Inside the Class:

    • Like having access to the contents of the locked box, methods within the class can directly modify private properties.
class MyClass {
    private $myProperty;

    public function modifyProperty($value) {
        $this->myProperty = $value;

$obj = new MyClass();
$obj->modifyProperty("Updated Value");

Using Reflection:

  1. Reflection:

    • Like using special tools to access the contents of the locked box, you can use Reflection to modify private properties from outside the class.
$obj = new MyClass();
$reflection = new ReflectionClass($obj);
$property = $reflection->getProperty('myProperty');
$property->setValue($obj, "Modified Value");


  • Modifying private properties directly from outside the class (using Reflection or other methods) can lead to unexpected behavior and violate encapsulation principles. It's generally better to use setter methods to modify private properties.

In PHP, private properties are intentionally restricted from direct modification to ensure proper encapsulation and data integrity. It's recommended to use setter methods or other appropriate methods within the class to modify private properties.

Previous articles of the series:

Mastering the PHP Developer Interview: 100+ Technical Questions Answered. 1-15.

Mastering the PHP Developer Interview: 100+ Technical Questions Answered. 16-30.

Mastering the PHP Developer Interview: 100+ Technical Questions Answered. 31-45.