Interview Cheatsheet for PHP Developers

Introduction

Being well-prepared for a PHP developer interview can greatly increase your chances of success. To help you in your preparation, we have compiled a cheatsheet that covers a variety of common interview questions and provides answers, along with relevant code examples and useful tips.

Problem-Solving Questions

1. Explain the difference between == and === operators in PHP.

   The == operator checks for equality, while the === operator checks for both equality and the same data type. For example:

   $var1 = 5;
   $var2 = '5';

   var_dump($var1 == $var2);   // Output: bool(true)
   var_dump($var1 === $var2);  // Output: bool(false)

2. How can you prevent SQL injection vulnerabilities in PHP?

   SQL injection vulnerabilities can be prevented by using prepared statements or parameterized queries. This involves using placeholders for dynamic data in SQL statements and binding the values separately. For example:

   $stmt = $pdo->prepare("SELECT * FROM users WHERE username = :username");
   $stmt->execute(['username' => $username]);

3. Explain the difference between include and require in PHP.

   The include statement includes and evaluates a specified file, while the require statement does the same but produces a fatal error if the file cannot be found or included correctly. For example:

   include 'config.php';  // file not found - produces a warning
   require 'config.php';  // file not found - produces a fatal error

4. How can you measure the execution time of a PHP script?

   The microtime() function can be used to measure the execution time of a PHP script. By calculating the difference between the start and end times, you can determine the script’s execution time. For example:

   Understanding Different Data Types in PHP

   $startTime = microtime(true);

   // ... PHP script code ...

   $endTime = microtime(true);
   $executionTime = $endTime - $startTime;

   echo "Script executed in: " . $executionTime . " seconds";

5. What are the differences between GET and POST methods in PHP?

• The GET method appends data to the URL and has limitations on the amount of data that can be sent. It is suitable for retrieving data.
• The POST method sends data in the HTTP request header and has no restrictions on the amount of data that can be sent. It is suitable for submitting data.

Object-Oriented Programming Questions

1. What is inheritance in PHP?

   Inheritance is a fundamental concept in object-oriented programming where a class can inherit properties and methods from another class. This promotes code reuse and allows for the creation of more specialized classes. For example:

   class Animal {
       protected $name;

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

       public function getName() {
           return $this->name;
       }
   }

   class Dog extends Animal {
       public function bark() {
           echo "Woof!";
       }
   }

   $dog = new Dog("Max");
   echo $dog->getName();  // Output: Max
   $dog->bark();          // Output: Woof!

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

• public visibility allows access from anywhere, both inside and outside the class.
• protected visibility allows access only within the class and its subclasses.
• private visibility allows access only within the class itself.

2. What are interfaces in PHP?

   Interfaces define a contract that classes must adhere to. They specify a set of methods that implementing classes must define. This promotes code consistency and enables polymorphism. For example:

   interface Logger {
       public function log($message);
   }

   class FileLogger implements Logger {
       public function log($message) {
           // Code to write the message to a file
       }
   }

   class DatabaseLogger implements Logger {
       public function log($message) {
           // Code to insert the message into a database
       }
   }

Conclusion

This interview cheatsheet provides an overview of important PHP topics that are often discussed during interviews. Remember, the key to success lies in both understanding the concepts and being able to demonstrate them with practical examples.

By familiarizing yourself with these questions and practicing your answers, you can boost your confidence and increase your chances of landing your dream PHP developer job. Good luck!

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