Top 30 PHP OOPS Interview Questions and Answers

PHP remains one of the most popular languages for web development, with 65% of developers using it, according to a Stack Overflow survey. This shows the high demand for skilled PHP developers, especially those with expertise in Object-Oriented Programming (OOP). Key concepts like inheritance, polymorphism, encapsulation, and abstraction are essential for writing clean, efficient, and scalable code. Companies often focus on these OOP principles during interviews to find developers who can create robust applications. To help you prepare, this guide covers important PHP OOP interview questions and answers. Use these to practice and boost your confidence for your next interview.

PHP OOPS Interview Questions and Answers For Freshers

If you’re an entry-level candidate preparing for a PHP OOPS interview, it’s important to have a solid grasp of the basics. Key concepts like classes, objects, inheritance, and encapsulation form the foundation of Object-Oriented Programming in PHP. In this section, we cover essential PHP OOPS interview questions and answers designed to help freshers confidently tackle their interviews and make a great impression.

Q1. What is Object-Oriented Programming?

Sample Answer: This is a programming paradigm that organizes software design around objects and classes rather than functions and logic. Objects contain data and methods that operate on the data. OOP focuses on four key principles: encapsulation (bundling data and methods), abstraction (hiding complex implementation), inheritance (reusing code across classes), and polymorphism (using methods in multiple forms). Popular OOP languages include Java, Python, and C++, making it ideal for modular, scalable, and maintainable software design.

Q2. What are the advantages of PHP OOP?

Sample Answer: PHP Object-Oriented Programming (OOP) offers several advantages, including code reusability through classes and inheritance, which reduces redundancy and promotes efficiency. Encapsulation ensures data security by controlling access to properties and methods. Polymorphism enables flexibility, allowing methods to behave differently based on context. Abstraction simplifies complex systems by hiding unnecessary details. Additionally, OOP enhances code maintainability, scalability, and modularity, making debugging, updating, and collaborating easier on large-scale applications.

Q3. What do you mean by a class and an object? How do they differ?

Sample Answer: A class in programming is a blueprint or template for creating objects. It defines the properties (attributes) and behaviors (methods) the objects created from it will have. An object is an instance of a class, representing a specific entity with its data. The main difference is that a class defines the structure and behavior. At the same time, an object is a concrete instantiation of that class, holding actual values for the attributes and executing the methods.

Q4. What is Abstraction?

Sample Answer: Abstraction is a fundamental concept in computer science and software development that simplifies complex systems by emphasizing the important features while hiding irrelevant details. It enables developers to work with high-level concepts rather than low-level implementation specifics. Abstraction is used in programming through functions, classes, and interfaces, enabling easier maintenance and scalability. It helps in managing complexity, improving code reusability, and allowing users to interact with systems without needing to understand their intricate workings.

Q5. What are the different types of Polymorphism?

Sample Answer: Polymorphism in programming refers to the ability of different objects to respond to the same method call in different ways. There are two main types:

• Compile-time Polymorphism (Static Polymorphism): Achieved through method overloading and operator overloading. The method to be invoked is determined at compile time.
• Runtime Polymorphism (Dynamic Polymorphism): Achieved through method overriding, where the method to be invoked is determined at runtime based on the object’s actual type.

Both types enhance the flexibility, reusability, and maintainability of code by allowing one interface to work with different data types or objects.

Q6. Can you differentiate between the final class and the final method?

Sample Answer: In Java, the “final” keyword is used to restrict inheritance and modification. A final class cannot be subclassed, meaning no other class can extend it. This is useful when you want to create immutable classes, like “string”. On the other hand, a final method cannot be overridden by any subclass. This ensures the method’s implementation remains unchanged in subclasses. While a final class prevents inheritance, a final method only prevents method overriding. Both concepts ensure that specific behavior or structure is preserved and cannot be altered by subclasses in the inheritance hierarchy.

Q7. What do you mean by an object in PHP and what are the different kinds of PHP variables in object-oriented programming?

Sample Answer: In PHP, an object refers to an instance of a class, which is a blueprint for creating objects. It encapsulates functions that operate on the data, making code modular and reusable. In object-oriented programming (OOP), variables are categorized into different types:

• Instance Variables: Defined inside a class and unique to each object.
• Static Variables: Belong to the class rather than an instance and can be accessed without creating an object.
• Global Variables: Available throughout the script and can be accessed inside objects.
• Constant Variables: Cannot be changed once defined.

Each type serves a specific purpose in managing data in OOP.

Q8. What is a constructor, manipulator, and destructor? 

Sample Answer: In object-oriented programming, a constructor is a special function that initializes objects of a class when they are created, setting default values or performing setup tasks. A manipulator is a function that alters the state or behavior of an object, often used with operators or stream handling (e.g., in C++, manipulators adjust input/output formatting). A destructor is a function invoked automatically when an object is destroyed, ensuring proper cleanup, such as releasing memory or closing files. Together, these functions help manage object lifecycle, resource allocation, and deallocation within a program.

Q9. What is a constructor, manipulator, and destructor?

Sample Answer: A virtual function is a function in a base class that is declared using the “virtual” keyword and is meant to be overridden in derived classes. It enables polymorphism, allowing the program to determine at runtime which functions to invoke, depending on the object type, not the pointer type.

A friend function is a function that is not a member of a class but has access to its private and protected members. It is declared using the “friend” keyword and can be a standalone function or part of another class, allowing specialized access to another class’s internals.

Q10. What is considered a function overloading and operator overloading?

Sample Answer: Function overloading and operator overloading are two distinct concepts in object-oriented programming.

Function overloading occurs when multiple functions have the same name but differ in the number or type of their parameters. The correct function is called based on the arguments passed during the function call, allowing for more flexible and readable code.

Operator overloading allows custom behavior for operators (like +, -, *, etc.) in user-defined classes. By overloading operators, you can define how standard operators work with objects of a class, improving clarity and enabling intuitive syntax for operations involving complex data types.

Pro Tip: To boost your chances of success, check out our course on how to ace coding interviews to enhance your skills further and prepare like a pro.

PHP OOPS Interview Questions and Answers For Mid-level Candidates

For mid-level candidates, PHP OOP interviews focus on testing both conceptual understanding and practical application of Object-Oriented Programming principles. This section highlights key questions and answers tailored to help you demonstrate your expertise in solving real-world PHP development challenges. Strengthen your preparation with these essential PHP OOP interview questions designed for mid-level professionals. Here are some of the top PHP OOPs interview questions and answers for mid-level candidates.

Q11. What does the term ternary operator mean?

Sample Answer: The ternary operator is a shorthand for an “if-else” statement in programming, used to evaluate a condition and return one of two values based on the result. It follows the syntax: “condition ? value_if_true: value_if_false”. If the condition evaluates to true, the operator returns the “value_if_true”; otherwise, it returns the value_if_false. This operator is commonly used to simplify code, making it more concise and readable. It is supported in many programming languages, such as JavaScript, C, and Python (using conditional expressions), and is particularly useful for simple conditional logic in a single line of code.

Q12. Mention different kinds of arguments.

Sample Answer: Arguments can be classified into various types based on their structure and purpose. Deductive arguments use logic to reach a certain conclusion if the premises are true, often following a general-to-specific approach. Inductive arguments derive probable conclusions based on specific observations or evidence, often generalizing patterns. Abductive arguments propose the most likely explanation for an observed phenomenon, focusing on plausibility. Analogical arguments draw comparisons between two similar cases to support conclusions. Causal arguments establish cause-and-effect relationships, explaining how one event leads to another. Lastly, prescriptive arguments offer recommendations or solutions based on values, ethics, or needs. Each type serves distinct purposes in reasoning and persuasion.

Q13. What do you mean by method overriding? Differentiate between overloading and overriding.

Sample Answer: Method overriding occurs when a subclass provides a specific implementation for a method already defined in its parent class. The method in the subclass must have the same name, return type, and parameters. It enables runtime polymorphism and ensures dynamic method dispatch. Here are some of the key differences between overloading and overriding: 

Feature	Overloading	Overriding
Method Name	The method name is the same, but the parameters (number or type) are different.	The method name, as well as the parameters, must be the same.
Occurrence	Overloading occurs within the same class.	Overriding occurs between a parent class and a child class.
Polymorphism	It supports compile-time polymorphism.	It supports runtime polymorphism.

Q14. What do you mean by exception handling?

Sample Answer: Exception handling is a programming mechanism to manage and respond to runtime errors or unexpected situations that occur during program execution. It ensures that the program can handle issues gracefully, without crashing or causing unexpected behavior. Exceptions are abnormal conditions such as division by zero, invalid input, or file access failure. In most programming languages, exceptions are managed using constructs like try, catch, throw, and finally. When an exception occurs, the program flow jumps to a corresponding handler to address the issue, allowing developers to implement corrective actions or log errors while maintaining program stability and user experience.

Q15. What do you mean by access modifiers?

Sample Answer: Access modifiers in programming are keywords used to define the visibility or scope of a class, method, or variable. They control which parts of the code can access specific members, ensuring proper encapsulation. Common access modifiers include public, private, protected, and default.

• Public: The member (class, method, or variable) is accessible from any other class or object, regardless of its location in the program.
• Private: The member is accessible only within the class in which it is defined. Other classes cannot access it directly.
• Protected: The member is accessible within its class and by subclasses (derived classes) but not by other classes.
• Default: If no access modifier is specified, the member is accessible only within classes in the same package.

Access modifiers improve code security, prevent unintended data modification, and enforce a structured and maintainable code design.

Q16. What is the function of a pure virtual function? Give an example.

Sample Answer: A pure virtual function in C++ is a virtual function declared in a base class but not defined, requiring derived classes to provide their implementation. It is specified by assigning 0 in its declaration. A class containing pure virtual functions becomes an abstract class, meaning objects of this class cannot be instantiated directly. Pure virtual functions enforce a contract for derived classes to implement specific behavior.

Example:

#include <iostream>
using namespace std;

class Shape {
public:
    virtual void draw() = 0; // Pure virtual function
};

class Circle: public Shape {
public:
    void draw() override { cout << "Drawing Circle\n"; }
};

int main() {
    Circle c;
    c.draw(); // Output: Drawing Circle
    return 0;
}

Here, “Shape” is abstract, and “Circle” implements “draw()”.

Q17. State all the operators which cannot be overloaded.

Sample Answer: In C++, certain operators cannot be overloaded to maintain language consistency and prevent ambiguity. These are:

• Scope resolution operator (::)
• Sizeof of operator (sizeof)
• Member selector (.)
• Member pointer selector (.*)
• Ternary/conditional operator (?:)
• Typeid operator (typeid)
• Alignof operator (alignof)
• “new” and “delete” cannot be overloaded globally, only replaced.

These restrictions ensure clarity and safeguard core language behavior.

Q18. Give examples of constants in PHP along with their purpose.

Sample Answer: In PHP, constants are immutable values defined using the “define()” or the “const” keyword. Examples include:

• “PI: define(‘PI’, 3.14159);” – Used for mathematical calculations involving circles.
• “SITE_URL: define(‘SITE_URL’, ‘https://example.com’);” – Holds the website’s base URL.
• “MAX_USERS: const MAX_USERS = 100;” – Specifies application limits, like user caps.

Constants enhance code clarity, and maintainability, and prevent accidental value changes.

Q19. What is polymorphism?

Sample Answer: Polymorphism, a core concept in object-oriented programming (OOP), allows objects of different classes to be treated as objects of a common superclass. It enables a single interface to represent different underlying data types, fostering flexibility and reusability. Polymorphism is achieved through method overriding (runtime polymorphism) and method overloading (compile-time polymorphism). For instance, a parent class reference can invoke a child class method dynamically, facilitating code scalability, abstraction, and maintainability across applications.

Q20. What is meant by Structured Programming?

Sample Answer: Structured programming is a programming paradigm that emphasizes breaking down a program into smaller, manageable modules or functions, enhancing code readability and maintainability. It uses a clear control flow through constructs like sequence (executing statements in order), selection (if-else), and iteration (loops). Structured programming avoids goto statements, reducing complexity and errors. By encouraging modular design and a top-down approach, it promotes logical organization, and ease of debugging, and simplifies understanding of large codebases.

PHP OOPS Interview Questions and Answers For Experienced Candidates

This section provides a comprehensive list of PHP OOPS job interview questions tailored for experienced candidates. It focuses on advanced concepts helping professionals prepare effectively for technical interviews and demonstrate their expertise. Here are some of the top PHP OOPs interview questions and answers for experienced candidates.

Q21. What are access specifiers and what is their significance?

Sample Answer: Access specifiers are keywords in programming that define the visibility and accessibility of class members (variables, methods) in object-oriented languages. Common access specifiers include public, private, and protected. Public members are accessible from anywhere, private members are restricted to the defining class, and protected members are accessible within the class and its subclasses. Their significance lies in controlling data encapsulation, ensuring security, and promoting modularity by restricting unintended access to sensitive parts of code.

Q22. What is an abstract class? How is an abstract class different from an interface?

Sample Answer: An abstract class is a class that cannot be instantiated directly and is designed to be inherited by other classes. It can contain both abstract methods (without implementation) and concrete methods (with implementation). Abstract classes are used to define common functionality that subclasses must implement or inherit.

An interface, on the other hand, defines only abstract methods and cannot contain implementation. A class that implements an interface must provide concrete implementations for all of its methods. The key difference is that a class can implement multiple interfaces but can inherit from only one abstract class.

Q23. What is the meaning of exception handling?

Sample Answer: Exception handling is a programming concept used to manage runtime errors or unexpected situations that disrupt the normal flow of a program. It allows developers to write code that can anticipate potential errors, detect them, and respond with a predefined course of action, such as logging the error or providing user feedback. This process enhances the program’s robustness and stability, ensuring it doesn’t crash abruptly and providing a controlled way to handle errors and exceptions.

Q24. What is meant by Garbage Collection in the OOPS world?

Sample Answer: Garbage Collection in Object-Oriented Programming (OOP) refers to the automatic process of reclaiming memory that is no longer in use. It involves identifying and deleting objects that are no longer reachable or referenced by the program. This helps prevent memory leaks, ensuring efficient memory management. Garbage Collection is typically handled by the runtime environment (like JVM in Java or CLR in .NET) to reduce the programmer’s burden of manual memory management and improve application performance.

Q25. How does C++ support Polymorphism?

Sample Answer: C++ supports polymorphism through function overloading, operator overloading, and inheritance, enabling objects of different types to be treated as instances of a common base type. It primarily achieves polymorphism via virtual functions and overridden methods. When a base class function is declared as “virtual”, C++ allows derived classes to provide their specific implementations. This enables dynamic method dispatch, where the function that gets called is determined at runtime based on the object’s actual type, not its reference type.

Q26. What is the meaning of NULL?

Sample Answer: The term “NULL” refers to a special marker used in programming, databases, and computer science to represent the absence or lack of a value. It indicates that a variable or data field has no value assigned, or that the value is unknown or undefined. NULL is different from zero, empty strings, or other default values, as it explicitly signifies the absence of data. It is commonly used in databases to handle missing or optional data fields.

Q27. State the differences between PHP constant and variable in object-oriented programming.

Sample Answer: In PHP, both constants and variables are used to store data, but they have different behaviors and use cases, especially in object-oriented programming (OOP). Here are the key differences:

PHP Constant	PHP Variable
A fixed value that cannot be changed once defined.	A dynamic value that can be modified during execution.
Declared using the const keyword.	Declared with the $ symbol (e.g., $variableName).
Cannot be modified once defined.	Can be modified or reassigned during program execution.
Used for values that should remain constant (e.g., configuration settings, mathematical constants).	Used for dynamic data that may change throughout the program’s execution.
Accessed using self::CONSTANT_NAME within a class.	Accessed using $this->variable_name (instance variables) or self::$variable_name (static variables).
Typically used in classes, but can also be global.	Can be instance-specific or static (shared across instances).
Often declared as public, protected, or private.	Can be public, protected, or private, depending on the desired access level.
Constants are typically written in uppercase letters (e.g., MAX_VALUE).	Variables typically follow camelCase or snake_case conventions (e.g., $userName).

Q28. What are the three scope levels available in PHP? Define them.

Sample Answer: In PHP, there are three primary scope levels: local, global, and static.

• Local Scope: Variables declared inside a function or method are accessible only within that function. They are not accessible outside of it.
• Global Scope: Variables declared outside any function or class are in the global scope. These variables can be accessed globally but require the “global” keyword to be accessed inside functions.
• Static Scope: A static variable retains its value across multiple function calls. It is declared inside a function using the “static” keyword, preserving its state between executions.

Q29. What types of rules are considered to determine the “truth” of any value that is not already because of Boolean type?

Sample Answer: To determine the “truth” of any value, not inherently Boolean, programming languages often use type coercion rules. These rules specify which values are considered true or false in conditional expressions. Typically, values such as “0”, “null”, “undefined”, “false”, “NaN”, and empty strings (“”) are evaluated as false. Everything else, including non-zero numbers, non-empty strings, and objects, is treated as true. These rules help simplify logical operations and allow broader data types to be used in conditions.

Q30. State the differences between PHP4 and PHP5.

Sample Answer: PHP4 and PHP5 are both versions of the PHP programming language, but PHP5 introduced several major improvements over PHP4. Below are the key differences:

PHP4	PHP5
PHP4 had limited support for OOP.	PHP5 introduced improved OOP support with features like classes, interfaces, and constructors/destructors.
PHP4 used the original Zend Engine.	PHP5 introduced Zend Engine 2, which improved performance and memory usage.
PHP4 did not support exceptions.	PHP5 added support for exceptions, enhancing error handling.
PHP4 had basic XML handling.	PHP5 introduced the SimpleXML extension, offering better XML support.
PHP4 had basic MySQL support.	PHP5 introduced MySQLi and PDO extensions, offering better database interaction and security.
PHP4 was less scalable and maintainable.	PHP5 improved scalability, maintainability, and overall robustness.

Tips to Prepare for PHP OOPS Interview

Object-Oriented Programming (OOP) in PHP is a critical skill sought after by employers in the software development landscape. As PHP continues to dominate backend web development, mastering OOP concepts will give you an edge in interviews. Preparing well showcases your technical expertise, problem-solving approach, and coding efficiency. Below are five key tips to help you confidently tackle a PHP OOPS job interview.

1. Master the Core OOP Concepts: Understand and be able to explain fundamental OOP principles: Encapsulation, Inheritance, Polymorphism, and Abstraction. Employers often test your ability to implement these concepts in PHP through real-world coding examples.
2. Practice PHP-Specific OOP Syntax: Be fluent in PHP OOP features like classes, objects, constructors, destructors, interfaces, traits, access modifiers (public, private, protected), and namespaces. Writing clean and structured PHP code is essential.
3. Understand Design Patterns: Study common design patterns like Singleton, Factory, Strategy, and Observer, as they are widely used in PHP applications. Be ready to explain where and how to implement these patterns in a project.
4. Work with Real-World Projects: Enhance your understanding by building or reviewing projects that involve MVC architecture, dependency injection, and database interactions using PHP OOP. Hands-on experience demonstrates practical knowledge.
5. Prepare for Code Review and Problem Solving: Employers may test you with coding challenges or ask you to review and optimize OOP code. Practice writing efficient, reusable code, and be prepared to explain your logic during code walkthroughs.

Top Companies Hiring for PHP OOPS Role

Companies across various sectors, including IT services, e-commerce, fintech, and digital media, are actively seeking skilled professionals. These professionals should be able to leverage PHP OOPS concepts to deliver efficient and robust solutions. Below is a list of top companies currently hiring for PHP OOP job roles in India, offering excellent career growth and learning opportunities.

1. TCS (Tata Consultancy Services)
2. Wipro Technologies
3. Capgemini
4. Accenture
5. Infosys
6. Cognizant Technology Solutions
7. Tech Mahindra
8. HCL Technologies
9. Mindtree
10. L&T Infotech

Conclusion

Mastering PHP OOPS interview questions is essential for securing roles in PHP development. A strong understanding of object-oriented programming concepts demonstrates expertise and problem-solving skills, helping you stand out. Regular practice and clear fundamentals will enhance your confidence and performance in any PHP OOPS job interview. If you are interested in C++ coding jobs, check our blog on the top C++ coding interview questions to ace your interview.

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