How to Hire PHP developers? (With interview Questions)

In this blog post, we discuss how to hire PHP developers, and also look at some important PHP interview questions.

So, if you’re a hiring manager looking to hire PHP developers(full-time/freelance) or a developer looking for interview questions this guide is exactly the place for you.

Before diving into this article, I want to tell you my motivation behind writing this blog. Being a developer myself, like any normal person, I’ve googled ‘interview questions’ before any interview, and that hasn’t changed even now. I’m working at Flexiple, where we hire the top 1% developers for top companies based on their requirements. I have tried my luck looking up for interview questions online but have always found mediocre content.

This is my attempt to answering two main questions:

1. How to hire PHP developers?
2. What are some important PHP interview questions?

How to Hire Freelance PHP developers?

There is no right or wrong way to hire PHP developers but I’ll quickly share everything that we have learned over 4 years of hiring developers. We’ve interviewed over 15000 developers and helped over a hundred clients find the perfect developer for their requirements.

It is a given that 79% of websites whose server-side programming language is known are built using PHP. Ever wondered what the hype around PHP is all about?

Well,

1. PHP is easy to integrate with other technologies such as Java- does not require re-development.
2. PHP can fix errors quickly, making it easy to maintain. Further, PHP is considered to be a comparatively easy language to learn. This attracts newbies, who can make dynamic websites with minimum programming expertise. However, this also makes hiring a great PHP developer challenging.

To filter out from the lot here are a few things you should consider when writing the Job Description(JD):

1. Years of software development experience: Be specific about the number of years of experience needed and the technology you’re looking for. A proxy to years of experience can be the number of production-level apps worked on.
2. Expertise in particular PHP frameworks/versions: Each PHP framework has its peculiarities and nuances. While good PHP developers can pick up other frameworks, it’s a plus point to hire a developer who already has expertise in it.
3. Type of products built in the past: You can filter out applications based on the candidate’s past work if you want someone who has a fair idea about how things work in a product like yours.
4. Exposure to certain industries: Developers who have built products in certain industries will already know key aspects of laying the foundation for a great product and will be able to predict possible problems.
5. Experience working remotely: Hiring someone who has worked remotely in the past is an added benefit as they have front-hand experience of everything right from how the contracts work to communication and from timelines to deliverables.
6. Strong communication: An essential thing to look at when hiring a freelancer is good communication skills. Since all the communication happens online, a freelancer needs to be able to seek to understand and be direct in their language.

What are some important PHP interview questions?

Once you have a filtered list based on your requirements you can then focus on selecting the right candidate. It all boils down to the technical interview round. We divide our questions into three sections:

A. Basic concepts: Includes all basic concepts used across languages but we've focused on their significance in PHP. This will give you an understanding of how strong their programming foundation is.

B. Advanced concepts: Includes all concepts that someone with higher expertise should know.

C. DS/Algorithm questions: To test the logical capability of the candidate.

To give you an idea, here’s a sample list with one question each(to keep the blog of desirable length):

1. Basic concepts:

Q. What are the magic methods in PHP? List 5 magic methods and explain each with an example.
Answer: Magic methods are methods that are automatically triggered in response to a particular PHP event.
To invoke any user-defined function in PHP, you need to make a function call. A magic method is special since it doesn’t require an explicit function call. It is invoked automatically when an event is triggered.

Rules of function definition of a magic method:

1. The method name must begin with 2 underscores (__).
2. The method should be defined inside the class.
3. The method should be declared public.

PHP magic methods invoked on creating a class instance are:

1. __construct() This method is called when an object is instantiated. The purpose of the construct() method is to assign some default values to object properties. In the OOPS paradigm, this is the parallel for a constructor. Typically, this should be the first thing in your class declaration. However, just like any other method, you can choose to declare it anywhere in the class body.

Example:

class Employee{
    private $name;
    private $email;

    public function __construct($name, $email)
    {
        $this->name = $name;
        $this->email = $email;
    }
}

$objEmployee = new Employee('Sam', ‘sam@robustplus.com');

In the above example, when a new employee is instantiated with name- Sam and email- sam@robustplus.com, the magic method construct is called. The __construct() method assigns values passed in the arguments to the respective object properties.

2.__destruct()
This method is called when the object is destroyed or no longer has any references either by PHP itself or explicitly by the user. It could also be called when the script stops or is exited.

Example:

class Employee{
    private $name;
    private $email;

    public function __construct($name, $email)
    {
        $this->name = $name;
        $this->email = $email;
    }

    public function __destruct()
    {
        echo 'This will be called when the script stops.';
    }
}

$objEmployee = new Employee('Sam', ‘sam@robustplus.com');

PHP magic methods used to deal with inaccessible class members created at runtime by the concept of PHP overloading.

3.__get($property)
This method is called when you try to read data from inaccessible or non-existent object properties. This method helps you to get values for such dynamic object properties.

Example:

class Employee{
    private $data = array();

    public function __set($name, $value)
    {
        $this->data[$name] = $value;
    }

    public function __get($name)
    {
        If (isset($this->data[$name])) {
            return $this->data[$name];
        }
    }
}

$objEmployee = new Employee();
echo $objEmployee>phone;            // __get is called

4.__set($property, $value)
This method is called when you try to set data to inaccessible or non-existent object properties. This method helps you to get values for such dynamic object properties.

Example:

class Employee{
    private $data = array();

    public function __set($name, $value)
    {
        $this->data[$name] = $value;
    }

    public function __get($name)
    {
        If (isset($this->data[$name])) {
            return $this->data[$name];
        }
    }
}

$objEmployee = new Employee();
$objEmployee>phone = '5879584623';              // __set is called

5.__isset($content)
This method is called when a call to the isset() method is made on inaccessible or non-existent object properties. In simpler terms, it is invoked automatically while checking whether a required overloaded property is set or not.

Example:

class Employee{
    private $data = array();

    public function __isset($name)
    {
        return isset($this->data[$name]);
    }
}
$objEmployee = new Employee();
echo isset($objEmployee>phone);

2. Advanced concepts:

Q. What is the factory pattern? How would you implement it in PHP?
Answer: Design patterns in PHP act like blueprints that can be customized to solve a recurring software design problem. These patterns provide well tested, proven development/design paradigms that help to speed up the development process. Using design patterns, you can make your code more reusable, flexible, and maintainable.

PHP has 3 design patterns-

1. Creational patterns: These patterns are used to construct objects that can be decoupled from their implementing system.
2. Structural patterns: These patterns are used to form object structures between many different objects
3. Behavioral patterns: These patterns are used to manage relationships, algorithms, and responsibilities between objects.

The Factory design pattern is one of the most used creational design patterns. It solves the problem of creating product objects without specifying their concrete class by maintaining a dedicated class responsible only for making objects. It is recommended to use the factory pattern when the subclass of an object instantiated can vary.

Example:

class Digital
{
    private $mobileMake;
    private $mobileModel;
    public function __construct($make, $model)
    {
        $this->mobileMake = $make;
        $this->mobileModel = $model;
    }
    public function getMakeAndModel()
    {
        return $this->mobileMake . ' ' . $this->mobileModel;
    }
}
class DigitalFactory
{
    public static function create($make, $model)
    {
        return new Digital($make, $model);
    }
}

$honor = DigitalFactory::create('Honor', '10 Lite');
print_r($honor>getMakeAndModel()); // outputs "Honor 10 Lite"

This code uses a 'DigitalFactory' to create a Digital object. The 2 benefits of doing this are:

1. You can change, rename, or replace the Digital class whenever you need to- all you have to do is modify the code in the 'DigitalFactory', instead of every instance of the class in your project.
2. Instead of creating a new instance every time you want to create an object- you can simply do all the work in the factory and reuse it.

3. Ds/ Algorithm:

Q. Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid. An input string is valid if: Open brackets must be closed by the same type of brackets. Open brackets must be closed in the correct order. Note that an empty string is also considered valid.
Answer:

$result = hasMatchedParenthesis(")("); 
echo $result;
function hasMatchedParenthesis($string) {
        $len = strlen($string);
        $string_check = 1;
        $stack = [];
        for ($i = 0; $i < $len; $i++) {
            switch ($string[$i]) {
                case '(': array_push($stack, 0); 
                break;
                case ')':
                    if (array_pop($stack) !== 0)
                        return 0;
                break;
                case '[': array_push($stack, 1); 
                break;
                case ']':
                    if (array_pop($stack) !== 1)
                        return 0;
                break;
                case '{': array_push($stack, 1); break;
                case '}':
                    if (array_pop($stack) !== 1)
                        return 0;
                break;
                default:
                       $string_check = 0 ;
                break;
            }
        }
        return ($string_check ? empty($stack) : 0);
} 

: The above code will input 0(false).

You can find all other interview questions here: PHP interview questions.

Where to find good freelance PHP developers?

As discussed, it isn't easy to find a quality PHP developer but this guide makes the process easier for you. To offload the entire hiring process, reach out to us at Flexiple. We've designed a high-quality, 6-step screening process to find the top 1%, freelance developers. You can find the best freelance PHP developers here.

Lastly, to quickly summarize it for you:

1. Note your project requirements and hire accordingly. Do not go for the lowest or the highest-paid developer.
2. Don’t hire without vetting- consider asking questions right from the basics to advanced to logical questions.
3. Look for companies like Flexiple that help you find the perfect fit.

I hope this blog helps you find the perfect PHP developer. I have a more detailed version of this blog, you can check it out to get more in-depth knowledge. :)