Table of contents

Introduction

PHP oops Interview Questions For Freshers

Q1. What is the use of PHP language?

Q2. Is PHP an object-oriented language?

Q3. What is the advantage of using PHP language?

Q4. What do you mean by object-oriented programming?

Q5. What are the characteristics of OOPs?

Q6. What is a class and object?

Q7. What do you mean by Inheritance?

Q8. What is Polymorphism?

Q9. How is the static keyword used in the program?

10.

Q10. Name the types of constructors.

Intermediate PHP oops Interview Questions

Q11. What is the use of echo and print commands in PHP?

Q12. What do PHP namespaces mean?

Q13. Describe the types of access modifiers in PHP.

Q14. Is operator overloading supported by PHP?

Q15. What is the difference between encapsulation and abstraction?

Q16. What is the purpose of the yield keyword in PHP?

Q17. What are the types of Polymorphism?

Q18. What is the use of traits in PHP?

Q19. Differentiate between require() and include() function in PHP?

10.

Q20. What is the use of the finalize method?

Advanced PHP oops Interview Questions

Q21. Explain Polymorphism with the help of an example.

PHP

Q22. What is the use of the final keyword in PHP?

PHP

Q23. Differentiate between abstract class and interface.

Q24. What do you understand about Type Hinting in PHP?

PHP

Q25. Differentiate between PHP4 and PHP5.

Q26. What is the purpose of a pure virtual function?

10.

Q27. What is Interface in PHP?

11.

Q28. What does the term "NULL" mean?

Frequently Asked Questions

What are the OOP concepts in PHP interview?

How do I prepare for an OOP interview?

How do you answer OOPs concepts in an interview?

Conclusion

Last Updated: Jun 12, 2024

Medium

Most Asked PHP oops Interview Questions and Answers

Author Soumya Agrawal

Introduction

A programmer comes across two programming languages- Object oriented and procedural programming .Object oriented programming languages have several advantages compared to procedural languages: OOP provides clear and easier code to execute, and makes the code easier to understand, modify, and debug.

In this article we will go through some frequently most asked PHP oops interview questions and answers.

PHP oops Interview Questions For Freshers

Below are some php oops interview questions and their answers.

You can navigate between easy, medium, and hard questions according to your interview phase.

Let's Begin!

Q1. What is the use of PHP language?

Ans: A server-side scripting language that helps developers to create dynamic web pages. Its main goal is to make web servers that can fetch data from different forms, create web pages, send and receive cookies, etc. Some big giants, like Facebook, Lyft, Drupal, etc., need PHP developers in great numbers.

Q2. Is PHP an object-oriented language?

Ans: Yes, PHP is based on C++ language, which is an object-oriented language, and therefore PHP is an object-oriented programming language that supports various concepts except for Multiple Inheritance.

Q3. What is the advantage of using PHP language?

Ans: The advantages of using PHP are as follows:

Easy Maintenance

Open Source platform

Highly Flexible and adaptable

Simple to learn

Scalable

Efficient

Q4. What do you mean by object-oriented programming?

Ans: An object-oriented programming language is an approach that enables programmers to create secure and flexible applications using independent objects that can be modified or reorganized without affecting the other parts of the program.

Q5. What are the characteristics of OOPs?

Ans: The top Characteristics of OOPS are:

Classes and Objects

Encapsulation

Abstraction

Inheritance

Binding

Message Passing

Q6. What is a class and object?

Ans: Class: A class is a blueprint for an object. It defines properties and other functions associated with the object. It is created using the "class" keyword.

Syntax

<?php
class Color{
  // Statement
}
?>

Object: Each object has its own properties and functions defined under the class. They can interact without having information about each other. It is created using a "new" keyword.

For example, Dog is the object of the breed name Labrador Retriever, having its properties and behaviors.

Q7. What do you mean by Inheritance?

Ans: Inheritance in oops(object-oriented programming) happens when a class inherits properties from other classes. The class which inherits properties and methods from the other class is known as the child class, and the class from which the properties are inherited then it is known as the parent class. The child class uses extend keyword to inherit the properties of the parent class, and it can also have its own properties and methods.

Let’s go through the example below for a better understanding.

Q8. What is Polymorphism?

Ans: Polymorphism characteristic of oops means to have the same name of the function performing different operations/tasks. It has the ability to display the message in more than one form. Let’s take a look at this example, women play different roles. She can be a mother, wife of someone, HR in an organization, and many more simultaneously. So a single woman performing different tasks/roles is polymorphism.

Q9. How is the static keyword used in the program?

Ans: The static keyword is a non-access modifier that defines the static variables and methods common to all objects. The static properties and methods can be used directly without creating an instance of the class.

For example, All the students in the same school have a common property of school name; therefore, we can make the variable school name static.

Q10. Name the types of constructors.

Ans: The three types of constructors in PHP are:

Default constructor: The constructor with no parameters

Parameterized constructor: The constructor with arguments is called a parameterized constructor

Copy constructor: This constructor will take the address of the other objects as a parameter

Intermediate PHP oops Interview Questions

In this section we will go through intermediate-level php oops interview questions and answers.

Q11. What is the use of echo and print commands in PHP?

Ans: The echo and print commands in PHP are used to get the output on the runtime environment. The difference between these two is that echo returns no value while print returns 1.

Example:

<?php echo "Command- echo";

print "Command- print"; ?>

Q12. What do PHP namespaces mean?

Ans: PHP namespaces prevent conflict between the classes with the same name so they can't be reused again. A namespace contains a regular valid PHP code and affects codes like interface, constants, and classes.

The namespace keyword is used for the declaration of the namespace at the top of the file.

Syntax

<?php
namespace Name{
  
    // Code
    function Ninjas()
    {
        echo 'Example';
    }
}
?>

Q13. Describe the types of access modifiers in PHP.

Ans: The three access specifiers in PHP are:

Public: The members of the class specified as the public can be accessible everywhere

Protected: The members of the class specified as protected can be accessible within that particular class and the derived class which extends this class

Private: The members of the class specified as private can be accessed only within that class

Q14. Is operator overloading supported by PHP?

Ans: Operator overloading means different types of operations are performed using the same operator. PHP doesn't support operator overloading and method overloading.

Q15. What is the difference between encapsulation and abstraction?

Ans: The difference between encapsulation and abstraction in PHP is:

Encapsulation	Abstraction
It is a process of containing information.	It is a process of obtaining information.
It is implemented using access specifiers.	It can be implemented using interfaces and abstract classes.
Encapsulation is a way of protecting the data.	Abstraction is a way of hiding unnecessary information.

Q16. What is the purpose of the yield keyword in PHP?

Ans: The yield keyword in PHP is used to return the data from the generator function. Generator functions are normal functions that act as iterators to be executed repeatedly. The yield keyword is the heart of the generator function that helps in yielding as many values as it needs.

Q17. What are the types of Polymorphism?

Ans: There are two types of Polymorphism:

Compile time Polymorphism (Method overloading)

Runtime polymorphism(Method overriding)

Method overloading: Method overloading is a static binding process where more than one method can have the same name but a different number of arguments.

But PHP does not support compile time polymorphism, which means our program will not contain properties like method overloading and operator overloading. Therefore only runtime properties or method overriding polymorphism is used.

Runtime Polymorphism: Runtime Polymorphism means the choice is made at runtime and not at the compilation time. Method overriding is a dynamic binding process where a subclass will have the same method name and number of arguments as the parent class/super class.

Q18. What is the use of traits in PHP?

Ans: Traits in PHP allow classes to inherit multiple behaviors by declaring methods in multiple classes, as PHP doesn't support multiple inheritances; therefore, OOP traits solve this problem. Traits can have methods with any access modifier. The trait keyword is used to create the traits. It helps developers to reuse methods kept in different inheritance hierarchies preventing code duplication.

Syntax

<?php
trait Name {
  // Code...
}
?>

Q19. Differentiate between require() and include() function in PHP?

Ans: The difference between require() and include() in PHP is:

require()	include()
This function will stop the execution of the script when any error occurs.	This function will not stop the execution of the script when any error occurs.
A fatal error (E_COMPILE_ERROR) along with the warning is produced by the require() function.	A warning (E_WARNING) is produced by the include() function and the script will continue to execute.
It gives a fatal error.	It does not give a fatal error.
The require() function is mostly used when the application requires a certain file.	When the file is not necessary and the application should continue running its process even if the file cannot be retrieved, the include() function is mostly used.

Q20. What is the use of the finalize method?

Ans: The use of the finalize method in PHP is to clean up the resources that are not in use. It is protected and only available through a derived class or another member of the same class.

Advanced PHP oops Interview Questions

Below are some advanced level php oops interview questions and answers. Let’s Begin!

Q21. Explain Polymorphism with the help of an example.

Ans: Polymorphism is an important object-oriented programming concept, which means the same name of the methods performing different operations. As you know, a person can possess different characteristics simultaneously so that Polymorphism can display the message in more than one form.

Advantages

It allows us to reuse the code
Easy to debug the codes

Usually, there are two types of Polymorphism- compile time polymorphism and runtime polymorphism but PHP does not support compile time polymorphism(method overloading).

An easy example to understand Polymorphism is through humans, like a person possessing different characteristics at the same time. He is someone's son, father, employee in the office, customer in the shop, etc.

Let’s go through an example to see polymorphism in PHP.

PHP

<?php
class main {
    function operation($x, $y) {
        $val = $x * $y;
        echo "After multiplying = " . $val;
    }
}
class Sub extends Main {
    function operation($x, $y) {
        $val = $x + $y;
        echo "After addition  = " . $val;
    }
}
$obj = new Sub();
$obj->operation(60, 90);
?>

Output

After addition = 150

Explanation:

In the above example the “Main” class is created with a function “operation” with x and y variables. In that function “val” variable is created to store the multiplication value of x and y variables. And the echo statement prints the function if it is called. The “Sub” class is used to extend the “Main” class in which the “operation” function is again created with x and y variables and “val” variable is used to store the sum. A new object is created and called by passing the values of x and y variables in the “operation” function.

Q22. What is the use of the final keyword in PHP?

Ans: The final keyword in PHP is used only for methods and classes. It prevents the subclass from overriding a method and prevents a class from being inherited.

Example:

PHP

<?php
  final class Main {
      function output() {
        echo "Main function";
      }
  }
  class Sub extends Main {
      function output() {
        echo "Sub class function";
      }
  }
  $obj = new Sub;
  $obj->output();
?>

Output

Explanation:

This code will throw error because we are creating “Sub” class from a final “Main” class.

Q23. Differentiate between abstract class and interface.

Ans: The main differences between abstract class and interface in PHP are:

Abstract class	Interface
It is under partial abstraction.	It is under full abstraction.
It is declared by using an abstract keyword.	It is declared by using the interface keyword.
Complete members of abstract classes can be static.	The members of the interface can not be static.
In abstract class a method must be declared as abstract.	All the methods in the interface are abstract by default.
The abstract methods can be protected or public.	The interface methods must be public.

Q24. What do you understand about Type Hinting in PHP?

Ans: The Type Hinting concept provides hints to function to accept the given data type as arguments. It can be used for arrays, objects, and callable data types.

Advantages

It helps in code debugging.

Helpful in static data.

Example

PHP

<?php

class example{
public $s= "Coding Ninjas";
}

function dis(example $val){
echo $val->s;
}

dis(new example());
?>

Output

Coding Ninjas

In the above example, the $val is of type "example" class passed to the "dis" function that displays the text of the class "example."

Q25. Differentiate between PHP4 and PHP5.

Ans: The difference between PHP4 and PHP5 is:

PHP4	PHP5
It is more procedure language.	It is an object oriented language.
In PHP4, everything(including objects) is passed by value.	In PHP5 all objects are passed by reference.
Magic Methods are not available.	Magic Methods are available.
It does not support abstract methods and classes.	It supports abstract class and methods.

Know What is Object in OOPs here in detail.

Q26. What is the purpose of a pure virtual function?

Ans: The aim of the pure virtual function is that it can be overridden within the child class, and it is a virtual function that doesn't have an implementation; it can be declared as pure using '=0'.

Example

virtual void func() // virtual // Not pure
virtual void func() = 0 // pure virtual

Q27. What is Interface in PHP?

Ans: Following are the properties of an interface in PHP.

Interfaces are declared using the interface keyword.

It allows us to specify the methods of a class

All methods in the interface must be public

To extend the interface class implement operator is used

The interface makes it easy to use different classes in the same way

Classes that are defined as interfaces are not to be instantiated

Q28. What does the term "NULL" mean?

Ans: It is a special data type in PHP that can only have a single value, NULL. If a variable is of data type NULL, no value is assigned. It can be represented as:

$var === null

Properties

In a boolean context, it turns out to be FALSE

The IsSet() function returns FALSE when testing with it is done

Frequently Asked Questions

What are the OOP concepts in PHP interview?

OOP principles in a PHP interview include classes and objects, encapsulation, inheritance, polymorphism, abstraction, and interfaces. The ability to understand how these ideas are applied in PHP for effective and modular code development may be a criterion for evaluation of candidates.

How do I prepare for an OOP interview?

Study OOP principles, perform coding exercises, comprehend design patterns, evaluate language-specific features, and be prepared to discuss your prior OOP projects are all things you should do to get ready for an Object-Oriented Programming (OOP) interview. To show your proficiency, practice using OOP ideas to solve problems and clear up any confusion.

How do you answer OOPs concepts in an interview?

Demonstrate your knowledge of classes, objects, inheritance, polymorphism, encapsulation, and abstraction in an OOP interview. Focus on modularity, maintainability, and code reuse while providing real-world examples and discussing relevant applications. Showcase the benefits of OOP principles in the efficient design and development of software.

Conclusion

This article discussed the most asked oop interview questions and answers. We have covered all the aspects of the PHP language.

Read out more articles on similar topics for further reading:

Refer to our Guided Path to upskill yourself in DSA, Competitive Programming, JavaScript, System Design, and many more! If you want to test your competency in coding, check out the mock test series and participate in the contests hosted on Coding Ninjas Studio!

Happy Learning!