21 Common OOP Interview Questions and Answers You Should Know Today

Object Oriented Programming interview questions help programmers and developers increase their knowledge about key concepts of the programming world.

OOP is one of the most necessary and necessary programming paradigms and focuses on objects and classes rather than procedures and functions.

OOP-based programming languages ​​include Objective-C, Java, Ada, Perl, Python, and C++.

Large companies are looking for developers who are familiar with object-oriented approaches and patterns.

So, if you are planning to participate in such an interview process, you should have a deep understanding of OOP concepts.

Let’s take a look at some of the common OOP interview questions and answers to help you prepare for the interview and test.

Object-Oriented Programming (OOP): An Overview

OOP is a programming paradigm that revolves around objects. Here, an object is considered to be a real-world instance, such as a class, that includes some behavior or characteristics specified in a class template.

For example, consider a car. According to the OOP model:

• Object : car. It can be any type or model, such as the car you own.
• Class : The model or type of car (BMW, Chevrolet, Kia, Audi, etc.).
• Features : car color, chassis number, engine type, gear type, etc.
• Behavior : How to change gears, how to start the car, etc.

Here, characteristics are also known as properties, attributes, or data, while behaviors are known as procedures, methods, or functions in programming languages.

So let’s start with some common OOP interview questions.

What does the term OOP mean?

Answer: Object-oriented programming (OOP) is a programming model based on objects and classes rather than procedures and functions. Individual objects are organized into classes. OOP uses concepts and programming paradigms such as polymorphism, hiding, and inheritance to describe real-world entities.

OOP binds code and data. Objects are real-world entities defined by classes with specific characteristics and behaviors, whereas classes are defined as patterns of specific objects. Also called user-defined data type.

This includes programs and mobile applications for design and manufacturing. For example, OOP can be used for manufacturing system simulation software.

What are the programming paradigms other than OOP?

Answer: A programming paradigm is a way of classifying programming languages ​​based on the characteristics of each language. There are two types of programming paradigms.

• Imperative programming paradigm: Focuses on how to execute logic and define control flow. This includes procedural programming paradigms, object-oriented programming (OOP), and parallel programming.
• Declarative programming paradigm: Focuses on what to do in a program and defines its logic, rather than control flow. This includes logical programming paradigms, functional programming paradigms, and database programming paradigms.

What is the difference between OOP and SOP?

Answer: Let us understand the difference between OOP and SOP using the following table.

What are the main features of OOP?

Ans: The main features of OOP are:

• inheritance
• encapsulation
• abstraction
• polymorphism
• Method override
• Method overloading
• object
• class
• constructor and destructor

Inheritance, polymorphism, and encapsulation are fundamental elements of OOP, and these features distinguish it from non-OOP languages.

What is encapsulation?

Ans: Encapsulation is a method of placing classes, variables, methods, etc. inside a capsule that is required to perform work and present the same capsule to the user. Simply put, all the necessary methods and data are brought together and unnecessary details are hidden from the user.

It can also be defined in other ways.

• Data binding: Encapsulation is the process of binding data members and methods as a class or as a whole.
• Data Hiding: Encapsulation is the process of hiding unnecessary information, such as restricting access to an object’s members.

What is polymorphism?

Answer: Let’s understand polymorphism by breaking it down into its two constituent words.

“Poly” means “many”

“Morph” means “shape”.

Polymorphism can therefore be described as objects having different shapes.

In OOP, it is referred to as a process in which some data, object, method, or code behaves differently in multiple contexts or situations. There are two types of polymorphism in OOP models.

• Runtime polymorphism
• Compile-time polymorphism

In other words, it’s multiple definitions of a single interface. For example, I have a class named “vehicle”, which consists of a method “speed”. It is impossible to define speed because different vehicles have different speeds. Therefore, this can be defined in different defined subclasses for different vehicles.

What is static polymorphism?

Answer: Static polymorphism is also called compile-time polymorphism. This is a feature that allows you to link objects to their respective operators or functions based on their values. This can be achieved through operator overloading or method overloading.

Here, the methods use similar names, but the parameters for each name are different. Objects behave differently for similar triggers. Therefore, multiple methods are implemented in the same class.

What is dynamic polymorphism?

Answer: Dynamic polymorphism is also known as runtime polymorphism. This refers to a type of polymorphism in OOP where the actual function inclusion is determined at runtime or runtime. This can be achieved by overriding methods.

For example, two classes are created, bike and Yamaha, and the class Yamaha extends the bike class by overriding the run() method. Subclass methods override parent class methods, so they are called at runtime.

What is a class?

Ans: A class can be defined as a blueprint or a template that contains some values ​​called member data. It also contains some rules called functions or behaviors. When you create an object, it automatically retrieves the functions and data defined in the class.

However, a class is a blueprint or template for an object. Based on the class, you can design as many objects as per your requirements. For example, first a car template is created. Then, based on the car template, different car units are designed.

What is an object?

Ans: An object can be defined as an instance of a class that contains instances of behavior and members defined in a template. An object is the actual entity that you interact with, whereas a class is just a blueprint for that object.

Therefore, objects have some characteristics or behavior and consume space (such as certain car models).

What is the difference between a class and a struct?

Answer: Let’s understand this using a table.

What is inheritance?

Ans: Inheritance is one of the features of OOP that allows a class to inherit key properties of another class. For example, if “vehicle” is a class, “car”, “bike”, etc. are other classes that can inherit key properties from class “vehicle”.

This feature helps remove redundant code. Therefore, the code size is smaller. Simply put, inheritance is defined as the receiver of properties from a parent class to a child class. Here, from the above example, “vehicle” is the parent class and “car” or “bike” is the child class.

This allows you to reuse programming code from one class in another class without having to write the same code again or wasting time in the process.

What are the different types of inheritance?

Ans: The OOP model uses different types of inheritance such as:

• Single inheritance: Defined as inheritance where a single class inherits the common functionality of a single base class.
• Multiple inheritance: Problems arise when a single class inherits from multiple classes.
• Multi-level inheritance: This means that a class inherits from other classes that are subclasses of other classes.
• Hierarchical inheritance: Refers to inheritance where one class has multiple subclasses.
• Hybrid inheritance: It is a combination of multilevel inheritance and multiple inheritance.

What are the restrictions on inheritance?

Answer: The limitations of inheritance include:

• Increases the effort and time required to run the program. This is because you have to jump frequently from one class to another, which takes time.
• Parent and child classes are very tightly coupled, making them less flexible.
• Must be carefully incorporated. Failure to do so may result in unsatisfactory or inaccurate results.
• A single change in a program can change the code in both the parent and child classes.

What is abstraction?

Ans: Abstraction is one of the elements of OOP. An important role of abstraction is to handle complexity. This is achieved by hiding unnecessary details from the user. This allows users to implement complex logic on top of the abstraction without considering hidden complexities.

For example, if you are a coffee lover, you need to know how much milk, coffee beans, and sugar cubes to add to make a cup of coffee using a coffee machine. It is pointless to think about the principle of operation of the machine. A coffee machine is a hidden complexity that you don’t need to know about, but the process of making coffee is essential.

There are two types of abstractions.

• data abstraction
• process abstraction

What is a constructor?

Ans: A constructor is a special method within a class or structure that has a name similar to the class name. This serves the necessary purpose of initializing the object. It is also useful for instantiating member data and methods that assign objects to classes.

When creating a constructor, you should keep the following in mind:

• It will be given the same name as the class name.
• It cannot be abstract, final, or static.
• There is no return type variable.

What are the different types of constructors in C++?

Ans: There are three main types of constructors in C++.

• Default constructor: A constructor that has no parameters or arguments in its definition. This type of constructor is used to initialize data members or variables with actual values.
• Parameterized constructor: Contains arguments or parameters in the declaration and definition. You can pass multiple parameters through a parameterized constructor. Used for overloading to know the difference between multiple constructors.
• Copy constructor: A member function that initializes an object using another object of a similar class. Additionally, it also helps in copying data from one object to another.

What is a destructor?

Ans: Destructor is a method that is automatically called during the destruction of an object. Implement specific actions.

• Recover previously allocated heap space during object initialization
• Close database connections and files
• Releasing network resources and resource locks
• Performing various household chores

In other words, the destructor destroys the object initialized by the constructor. This is a special member function that has the same name as the class name, but with a leading (~) symbol. Destructors are one-way functions, so they can be overloaded.

What is garbage collection (GC)?

Answer: Garbage collection (GC) is a memory recovery element built into programming languages ​​such as Java and C#. GC-enabled programming languages ​​include at least one garbage collector that automatically frees areas of memory that are no longer needed within a program.

Garbage collection ensures that the program is still within its memory quota. This removes the developer from manually managing the program’s memory and minimizes memory-related bugs.

What is exception handling?

Answer: Exception handling is a way to respond to unexpected events during the execution of a computer program. Programmers must “handle” unwanted events (exceptions) to prevent system or program crashes. Without this approach, exceptions can interrupt the common behavior of your program, creating inefficiencies or risks.

What is a Try/Catch block?

Ans: Try or catch are keywords that describe exception handling due to coding or data errors during program execution.

• A try block is a block of code that raises an exception.
• The catch block handles and catches the exception in the try block.

Try and catch statements are frequently used in various programming languages, including C++. C#, Java, SQL, JavaScript. Every try statement is matched with a catch statement to handle execution. There are a few more things to remember with Try and Catch statements.

• A try block is followed by a catch block.
• A try block is followed by at least one catch block.
• A try block is followed by another try block, which is followed by a catch block.

conclusion

OOP is an important concept that programmers should know. Learning it thoroughly will also help you program successfully in languages ​​that use OOP concepts.

If you are preparing for an interview or test, the above interview questions and answers will help you refresh your understanding of OOP concepts like classes, objects, encapsulation, polymorphism, inheritance, abstraction, etc. That way, you can approach the interview with confidence, successfully navigate it, and build your career.

You can also refer to some of these SQL interview questions.