PHP OOPs Interview Questions

Introduction

Welcome to this comprehensive guide on PHP OOP Interview Questions. If you’re preparing for an interview related to Object-Oriented Programming in PHP, you’ve come to the right place. In this article, we’ll delve into a series of questions and answers that will help you grasp the fundamentals of PHP’s Object-Oriented Programming, making you well-prepared for your upcoming interviews.

When a programmer encounters two programming paradigms, Object-Oriented Programming (OOP) and Procedural Programming, they will discover that OOP languages offer numerous benefits in contrast to procedural ones. OOP fosters code clarity and simplifies execution, making it more comprehensible, adaptable, and amenable to debugging.

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

PHP oops Interview Questions For Freshers

Q1. What is the use of PHP language?

Ans: PHP is a server-side scripting language utilized by developers to generate dynamic web pages. Its primary objective is to enable web servers to handle tasks like processing data from various sources, generating web content, managing cookies, and more. Notable companies like Facebook, Lyft, and Drupal often seek PHP developers due to the language’s significance in web development.

Q2. Is PHP considered an object-oriented language?

Ans: Yes, PHP is classified as an object-oriented programming language. It draws influence from languages like C++, which are object-oriented. PHP supports numerous object-oriented programming concepts, although it does not allow for Multiple Inheritance, a feature found in some other object-oriented languages.

Q3. What is the advantage of using PHP language?

Ans: PHP offers several advantages, including:

• Ease of Maintenance: PHP code is typically easy to maintain, thanks to its straightforward syntax and modular structure.
• Open Source: PHP is an open-source platform, making it cost-effective and accessible to a wide range of developers and organizations.
• Flexibility and Adaptability: PHP is highly flexible and can be used for various web development tasks, from simple scripts to complex applications.
• Ease of Learning: PHP is known for its simplicity and ease of learning, making it a suitable choice for beginners.
• Scalability: PHP applications can be scaled up to meet growing demands, making it suitable for both small and large projects.
• Efficiency: PHP is optimized for web development, offering efficient execution and performance for web applications.

These advantages make PHP a popular choice for web development projects.

Q4. What is object-oriented programming (OOP)?

Ans: Object-oriented programming is a programming paradigm that revolves around the concept of objects. It allows developers to design software using self-contained objects that encapsulate data and behavior. These objects can interact with each other, and the approach emphasizes modularity, reusability, and the ability to modify one part of a program without affecting others. OOP promotes code organization and design patterns that enhance the maintainability and scalability of software applications.

Q5. What are the key characteristics of OOPs?

Ans: Object-Oriented Programming exhibits the following fundamental characteristics:

• Classes and Objects: OOP is centered around the concept of classes, which define blueprints for creating objects. Objects, in turn, represent real-world entities or concepts with data and behavior.
• Encapsulation: Encapsulation involves bundling data (attributes) and methods (functions) that operate on that data into a single unit (class). It emphasizes data protection and access control.
• Abstraction: Abstraction allows developers to focus on the essential features of an object while hiding the complex implementation details. It simplifies problem-solving by presenting a high-level view.
• Inheritance: Inheritance enables the creation of new classes (derived or subclass) based on existing classes (base or superclass). It promotes code reuse and the establishment of relationships between classes.
• Binding: Binding refers to the association between methods and functions with their corresponding objects. It determines which method or function is invoked when a message is sent to an object.
• Message Passing: Objects in OOP communicate by sending messages to each other. This allows objects to interact and collaborate, facilitating dynamic and flexible behavior.

These characteristics collectively define the principles and structure of Object-Oriented Programming, which promotes modularity, maintainability, and code reusability.

Q6. What is a class and an object in OOP?

Ans: In Object-Oriented Programming (OOP):

• Class: A class serves as a blueprint or template for creating objects. It defines the attributes (properties) and methods (functions) that the objects will have. Classes are created using the “class” keyword and encapsulate the behavior and characteristics of objects.
  Syntax in PHP:

class ClassName {
  // Class members (properties and methods)
}

• Object: An object is an instance of a class. It represents a specific entity or concept defined by that class, with its unique set of data and behavior. Objects are created from classes and can interact with other objects and the program.

Using classes and objects, developers can model real-world entities in their code and create instances of those entities to work with.

Q7. What is Inheritance in OOP?

Ans: Inheritance is a fundamental concept in OOP where a class (known as the child or subclass) can inherit properties and methods from another class (known as the parent or superclass). The child class extends the functionality of the parent class, allowing it to reuse and build upon the parent class’s attributes and behaviors.

• The child class uses the extends keyword to inherit properties and methods from the parent class.
• It can also introduce its unique properties and methods, further customizing its behavior.
• Inheritance fosters code reuse, modularity, and the creation of hierarchical class structures, simplifying the design and maintenance of software systems.

Q8. What is Polymorphism in OOP?

Ans: Polymorphism is a key characteristic of OOP that allows a single function or method to exhibit different behaviors based on its context or the type of data it operates on. It enables the same function or method name to perform various tasks or produce different outcomes.

• Polymorphism simplifies code by offering a consistent interface for interacting with objects, regardless of their specific types.
• It enhances flexibility and extensibility in software design by enabling the substitution of objects of different classes that share a common interface.
• In OOP, polymorphism is often achieved through method overriding and interfaces, where different classes can provide their own implementations of the same method, tailored to their specific needs.

Q9. What is the purpose of the static keyword in a program?

Ans: The static keyword is a non-access modifier that is used to define static variables and methods within a class. Static members are shared across all instances (objects) of the class, and they can be accessed directly without the need to create an instance of the class.

For instance, when multiple objects share a common property or functionality, such as a school name in the case of students from the same school, the static keyword can be used to declare variables or methods that are common to all instances of the class, promoting efficiency and code organization.

Q10. What are the types of constructors in PHP?

Ans: PHP supports three types of constructors:

1. Default Constructor: A constructor with no parameters, which is automatically called when an object is created without specific arguments.
2. Parameterized Constructor: A constructor that accepts one or more arguments, allowing developers to initialize object properties during object creation.
3. Copy Constructor: This constructor is not directly supported in PHP. It typically takes another object as a parameter and creates a new object with the same values. In PHP, this functionality can be achieved through custom coding rather than a built-in copy constructor.

Intermediate PHP oops Interview Questions

In this section, we will discuss intermediate-level PHP Object-Oriented Programming (OOP) interview questions and answers.

Q11. What are the purposes of the echo and print commands in PHP?

Ans: In PHP, both echo and print are used to display output on the runtime environment. However, there are subtle differences between them:

• echo: The echo statement is used to output one or more values or expressions. It doesn’t return any value. It’s often used for displaying HTML content, variables, or strings.
  Example:

<?php
echo "This is the echo command";

• print: The print statement is also used for outputting values or expressions. However, it returns a value of 1 after execution. This makes it suitable for situations where you need to use it as part of a larger expression or condition.
  Example:

<?php
print "This is the print command";

Both echo and print are commonly used for generating output in PHP scripts, but the choice between them depends on the specific requirements of the task at hand.

Q12. What are PHP namespaces, and why are they used?

Ans: PHP namespaces are a way to encapsulate and organize code in such a way that it prevents naming conflicts between classes, functions, constants, and other identifiers. They are used to create a unique “namespace” for a group of related code elements, allowing developers to avoid conflicts when using libraries or working on large projects with many components.

Key points about PHP namespaces:

• Namespaces provide a solution to the problem of having multiple classes or functions with the same name in different parts of a project.
• They help improve code maintainability and organization by grouping related code under a common namespace.
• The namespace keyword is used to declare a namespace at the beginning of a PHP file, and it affects all the code within that file.
• By using namespaces, developers can ensure that their code remains clean, organized, and less prone to naming conflicts, especially in collaborative or complex coding environments.

Q13. Explain the types of access modifiers in PHP.

Ans: In PHP, there are three primary access modifiers that control the visibility and accessibility of class members (properties and methods):

1. Public: Members declared as public can be accessed from anywhere, both inside and outside the class. They have the broadest scope of visibility.
2. Protected: Members declared as protected can be accessed within the class where they are defined and within any subclasses that extend that class. They are not directly accessible from outside the class hierarchy.
3. Private: Members declared as private are the most restricted in terms of visibility. They can only be accessed within the class where they are defined. They are not accessible from derived classes or external code.

These access modifiers help enforce encapsulation and data hiding principles in object-oriented programming, ensuring that the internal implementation details of a class are not exposed unnecessarily and allowing for better control over the accessibility of class members.

Q14. Does PHP support operator overloading?

Ans: No, PHP does not support operator overloading. Operator overloading refers to the ability to define custom behaviors for operators (such as +, -, *, etc.) when applied to objects of a class. While some programming languages support operator overloading, PHP does not have this feature. Each operator in PHP has a predefined behavior, and it cannot be customized for user-defined classes.

Q15. Explain the difference between encapsulation and abstraction in PHP.

Ans: In PHP, encapsulation and abstraction are two fundamental concepts, and they serve different purposes:

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

Ans: The yield keyword in PHP is used within generator functions to produce a sequence of values one at a time. Generator functions are special functions that can be paused and resumed, allowing them to act as iterators.

• When a yield statement is encountered in a generator function, it returns a value and pauses the function’s execution, saving its state.
• The next time the generator is iterated (typically in a loop), execution resumes from where it left off after the last yield statement.
• This allows for efficient memory usage and lazy evaluation of sequences, especially for large datasets or infinite sequences.

Q17. What are the types of Polymorphism in OOP?

Ans: Polymorphism in Object-Oriented Programming (OOP) can be categorized into two main types:

1. Compile-time Polymorphism (Method Overloading): This type of polymorphism is also known as method overloading. It is a static binding process where multiple methods in the same class can have the same name but differ in the number or types of their parameters. The choice of which method to call is determined at compile time based on the method’s signature.Note: PHP does not support compile-time polymorphism, so method overloading is not available in PHP.
2. Runtime Polymorphism (Method Overriding): Runtime polymorphism, often referred to as method overriding, is a dynamic binding process. In this type of polymorphism, a subclass provides a specific implementation for a method that is already defined in its parent class (superclass). Both the subclass and superclass have methods with the same name and parameter list, but the actual method called is determined at runtime based on the object’s type. This allows for the customization of behavior in derived classes.

In most object-oriented languages, including PHP, runtime polymorphism (method overriding) is the primary form of polymorphism used, as method overloading is not natively supported.

Q18. What is the purpose of traits in PHP?

Ans: Traits in PHP are a mechanism that allows classes to share and reuse code across multiple class hierarchies. They address the limitation of single inheritance in PHP, as a class can use multiple traits, inheriting behaviors from all of them.

Key points about traits in PHP:

• Traits are created using the trait keyword, followed by the trait name and the code containing methods.
• Classes can use traits by including them using the use statement.
• Traits can contain methods with any access modifier (public, protected, or private).
• They help prevent code duplication by allowing developers to reuse methods in different class hierarchies.
• Traits are particularly useful when you want to share specific behaviors among unrelated classes without forming complex inheritance chains.

In summary, traits in PHP enhance code reusability and maintainability by enabling the composition of classes with shared functionality, overcoming the limitations of single inheritance.

Q19. Explain the differences between require() and include() functions in PHP.

Ans: In PHP, both require() and include() are used to include external files, but they differ in their behavior when encountering errors:

1. require() Function:
   • Error Handling: If the file specified in require() cannot be found or included, it will result in a fatal error (E_COMPILE_ERROR). This means the script execution will stop immediately, and the error message is displayed.
   • Use Case: require() is typically used when the included file is essential for the application’s operation. If the file is not found, the application should not continue running.
2. include() Function:
   • Error Handling: If the file specified in include() cannot be found or included, it generates a warning (E_WARNING) but does not stop the script execution. The script continues to run even if the inclusion fails.
   • Use Case: include() is used when the included file is not critical for the application’s functionality, and the application should continue running even if the file cannot be included.

In summary, the choice between require() and include() depends on the importance of the included file. Use require() when the file is essential, and use include() when the file is optional, allowing the script to continue executing even in case of inclusion errors.

Q20. What is the purpose of the finalize method in PHP?

Ans: The finalize method in PHP is used for cleaning up resources that are no longer in use, typically before an object is destroyed. It’s important to note that the finalize method is not a built-in feature in PHP. Instead, it can be implemented in a class by defining a custom method with the name __destruct().

• The __destruct() method is automatically called when an object is no longer referenced or goes out of scope.
• It allows developers to perform cleanup tasks, such as releasing database connections, closing files, or freeing up memory, before the object is destroyed.
• The __destruct() method is part of the PHP magic methods and is commonly used for resource management in classes.

So, while PHP does not have a finalize method per se, it achieves similar functionality through the __destruct() method for proper resource cleanup.

Q21. Explain the differences between abstract classes and interfaces in PHP.

Ans: Abstract classes and interfaces in PHP are both used to achieve abstraction and define contracts for classes to follow, but they have several differences:

Q22. What is an Interface in PHP?

Ans: In PHP, an interface is a contract that defines a set of methods that classes implementing the interface must adhere to. Interfaces are a fundamental part of object-oriented programming in PHP and serve several important purposes:

• Declaration: Interfaces are declared using the interface keyword.
• Method Specification: They specify a list of methods that must be implemented by any class that claims to implement the interface.
• Public Methods: All methods in an interface must be declared as public; they define the public API of the implementing classes.
• Implementation: To declare that a class implements an interface, you use the implements keyword.
• Common Interface: Interfaces make it possible to use different classes in a uniform way if they implement the same interface.
• Instantiation: Classes defined as interfaces cannot be instantiated; they serve as blueprints for classes that implement them.

Here’s a basic example of an interface in PHP:

interface Shape {
    public function calculateArea();
    public function calculatePerimeter();
}

Classes that implement this Shape interface must provide concrete implementations for the calculateArea() and calculatePerimeter() methods. Interfaces play a crucial role in achieving polymorphism and code organization in PHP.

Q23. What is the significance of the “NULL” data type in PHP?

Ans: In PHP, NULL is a special data type that represents the absence of a value. It is used to indicate that a variable has not been assigned any value or that a value has been explicitly set to NULL. Key points about the NULL data type include:

• Single Value: NULL can only have one value, which is NULL itself.
• Indicating Absence: It is commonly used to indicate that a variable or property does not have a valid value.
• Boolean Context: In a boolean context (e.g., when used in an if statement), NULL evaluates to FALSE.
• IsSet() Function: The isset() function returns FALSE when used to test a variable with a NULL value, indicating that the variable is not set.
• Initialization: Variables can be explicitly set to NULL using the assignment operator, e.g., $var = NULL;.

Using NULL is valuable when you need to distinguish between an intentionally unset variable and one that holds a specific value. It is an essential concept for handling missing or optional data in PHP applications.

Q24. Give a basic explanation of the Member Variable and Member function?

Ans:

Member Variable: Variables that are declared inside a particular class is called member variable of that particular class. The data declared inside a particular member variable of a call can only be accessed by the member functions of that particular class only, and no other function outside this class can access it or use it.

Member function – Functions that are defined inside a particular class are called member functions of that particular class. The function is basically used to access the member variable and use them; these member functions can only access the member variable of that particular class and are not eligible to access any variable outside this scope.

Q25. Explain Polymorphism with the help of an example.

Ans: Polymorphism is one of the fundamental concepts in object-oriented programming. It allows objects of different classes to be treated as objects of a common base class. In other words, it allows you to use a single interface to represent different types of objects. Polymorphism can be achieved through method overriding and interfaces in many object-oriented languages, including PHP.

Let’s illustrate polymorphism in PHP with an example:

Suppose we have a base class called Shape, which has a method calculateArea(). We also have two derived classes, Circle and Rectangle, both of which inherit from the Shape class. However, each derived class provides its own implementation of the calculateArea() method to calculate the area specific to its shape.

Here’s the code:

// Base class
class Shape {
    public function calculateArea() {
        // Default implementation for calculating area
        return 0;
    }
}

// Derived class 1
class Circle extends Shape {
    private $radius;

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

    public function calculateArea() {
        return 3.14 * $this->radius * $this->radius; // Area of a circle
    }
}

// Derived class 2
class Rectangle extends Shape {
    private $length;
    private $width;

    public function __construct($length, $width) {
        $this->length = $length;
        $this->width = $width;
    }

    public function calculateArea() {
        return $this->length * $this->width; // Area of a rectangle
    }
}

// Using polymorphism
$circle = new Circle(5);
$rectangle = new Rectangle(4, 6);

// Calculate and display areas
echo "Area of Circle: " . $circle->calculateArea() . " square units\n";
echo "Area of Rectangle: " . $rectangle->calculateArea() . " square units\n";

In this example, we have a base class Shape with a method calculateArea(), and two derived classes, Circle and Rectangle, each providing its own implementation of calculateArea(). When we create objects of these classes and call calculateArea() on them, the appropriate method is executed based on the object’s actual type. This is polymorphism in action – different classes, but a common interface (calculateArea()), allowing us to work with objects in a uniform way.

Conclusion

In this article about PHP OOP Interview Questions, we’ll cover a wide range of topics. To further explore PHP OOP concepts, you might find the official PHP documentation as a valuable resource. You can also check out tutorials on PHP OOP patterns on websites like W3Schools or PHP.net.