Commonly Asked OOPs Interview Questions

Commonly Asked OOPs Interview Questions
Commonly Asked OOPs Interview Questions


Object-Oriented Programming or OOP models can easily use or modify how programs and data interact with other objects. OOP Systems or OOPS make it easy to define the method during runtime and allow a diverse set of implementations.

OOP is one of the most popular models of programming and multiple popular languages such as C++, Java and Python follow the OOP methodology. Understanding the basic concepts of this programming paradigm can help answer most OOPS Interview Questions and reviewing commonly asked questions can help with Java OOPs interview questions or other OOPS technical interview questions.

Why is OOP important?

Object-Oriented Programming or OOP is one of the most highly effective programming paradigms that revolve around objects or classes containing specified characteristics and behaviour. Objects are assumed, implemented or declared instances of various entities that contain code and data.

In OOP, data can be contained through fields, procedures or simply code. The advantage of using this object-based approach can be observed through objects modifying and accessing the fields directly. 

OOP is important due to this model making it easy to create blueprints or templates through classes, based on which objects can be defined. This is a comparatively easy method of defining the instances of the classes and specifying the behaviour of the objects within the classes. Understanding the essentials of the OOP System can help answer many important OOPS interview questions.

Here are a few important advantages of using the OOP paradigm:

  • Easier troubleshooting due to modularity.
  • Identifying runtime errors and where to look for the issues.
  • Code can be easily reused due to inheritance features.
  • OOP is flexible, especially due to polymorphism
  • An effective way for declaring object behaviour
  • Efficient problem-solving

Characteristics refer to the description, attributes or properties of the objects while behaviour defines how objects are implemented or interact with the rest of the code.

Let’s check some examples of how classes, objects, characteristics or behaviour are used in the OOP approach.

  • Class: Dogs or Animals can be classes.
  • Object: In this case, specific dogs such as Labradors or an animal such as a bull are objects respectively.
  • Characteristics: Characteristics would be the colour of the labrador or the bull, their size, their weight or other features.
  • Behaviour: This defines or declares how the labrador or bull lives, eats and fundamentally functions. Behaviours are the functions given to the objects or their characteristics.

Top 17 Recurring OOP Questions and Answers

Here are some OOPS interview questions and answers that will definitely help during interviews. Object-Oriented programming interview questions are also important but can only be prepared with enough practice.

Other than that, revising these common OOPS viva questions and answers can definitely help answer most basic OOPS interview questions and explain some complex OOPs concepts. In Java interview questions or C++ interview questions as well, these curated sets of answers can help.

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1. What are some of the most important features of OOPS?

The main features that OOPS offers are polymorphism, abstraction of data, inheritance and encapsulation.

2. How can you define Polymorphism?

Polymorphism consists of ‘Poly’ and ‘morph’ fundamentally meaning ‘many’ and ‘shapes’, respectively. So, polymorphism refers to the feature of having many shapes. In programming, polymorphism can be defined as the ability to implement multiple approaches.

Static Polymorphism can be defined as polymorphism that occurs during compiling time while Runtime polymorphism occurs during execution.

3. Does C++ support Polymorphism and how?

Yes, C++ is an OOP language, therefore supporting Polymorphism. C++ supports static polymorphism using features such as default arguments, templates and function overloading while runtime polymorphism is supported through virtual functions.

During runtime polymorphism, virtual functions are used for taking identical functions based on the types of objects. These are finally implemented during compilation.

4. What do you mean by Structured Programming?

Structured Programming can be defined as programming that boasts of a structured control flow that is complete. Structures can also be referred to as blocks that contain sets of rules and are governed by definitive control flows. For example, if, then, while, else, for and other sub-routines.

The OOPS model features structure programming as it is one of the most fundamental controlled approaches for defining structures.

5. Can instance of abstract classes be created?

We cannot create instances of abstract classes as they do not have complete or absolute implementations. However, we can create instances of subclasses that inherit the abstract classes.

6. Describe method overloading.

This is one of the top 50 OOPS interview questions. Method loading can be defined as a valuable function of OOPS that allows multiple functions or methods to possess the same name. Even with identical method names, the arguments are different and the call-to-the-methods are resolved in accordance with these arguments.

7. What is Inheritance?

In OOP, inheritance can be defined as the process through which objects or classes are created by defining other objects or classes. The ‘child’ is the object that inherits while the ‘parent’ is where the attributes or behaviour is inherited from.

Inheritance allows implementations to become much simpler while also facilitating code reusability. Here are the five different types of inheritances:

  • Single inheritance
  • Hierarchical inheritance
  • Multiple inheritances
  • Hybrid inheritance
  • Multi-level inheritance

8. What is Garbage Collection in the OOP System?

OOPS is based on entities such as objects that consume memory with multiple objects in each class. So, it is crucial to control the memory and objects effectively, failing which might lead to errors, failures or even system crashes.

Fundamentally, garbage collection can be defined as the system of handling memory-related tasks in the program. Garbage collection helps in removing unwanted objects that are not required, thus freeing memory.

9. Can Java applications be executed without following OOP?

Java applications cannot be run without OOPS implementations. Java itself is based on the OOP System and it is an object-oriented programming language. Practising OOPS coding questions in Java and checking other Java OOPs coding questions is highly advised.

However, languages such as C++ can be used with or without OOPs. It is also advised to practise OOPS viva questions in C++ and prepare for the technical questions on the OOPS concept.

10. What are interfaces?

Interfaces are used for declaring a method without specifically defining this method. Interfaces must be defined by the classes that implement the methods of the interfaces. Interfaces, however, do not contain instructions or behaviours to be executed, and hence are not templates or blueprints for the program.

11. What is the main difference between classes and structures?

Classes are user-defined blueprints that cover the created objects and contain the sets of instructions or methods that must be passed through the objects. Meanwhile, structures are user-defined sets of variables that contain various data types.

12. What are pure virtual functions?

Pure virtual functions are abstract functions that only get declared in the base classes. A pure virtual function does not contain definitions in the base classes and must be redefined inside the subclasses.

13. What is Abstraction?

Abstraction can be defined as a method of hiding details that are not required from the important ones. Abstraction is one of the most primary features of the OOP system. For example, an animal’s behaviour might be known but how the animal does it or what goes on inside its body is not known.

14. What are exceptions?

Exceptions can be defined as special occurrences or events. These anomalies or events are raised during runtimes when programs are executed, fundamentally leading to the execution failing or stopping. Unspecified or undesirable inputs are two of the main causes that can lead to exceptions.

15. What is a superclass? 

Superclasses refer to the classes that allow other classes or any other class to inherit functions or behaviour. Animals would be the superclass of dog, bull and lion classes. This is only true if all these classes have inherited something from the same superclass.

16. What are constructors?

Constructors are special methods that share the name with the class. Constructors help in initialising objects and when classes are instantiated using member data. Constructors then use these methods or data for assigning them to objects.

17. What are destructors?

Destructors are special methods that free up memory or resources occupied by objects. Destructors are used when objects need to be removed and destroyed, fundamentally being automatically called during these scenarios. 

Frequently Asked Questions

How do you explain OOP to an interview?

OOP is a programming paradigm that is simply not based on methods, procedures or functions but is more focused upon objects. OOPS integrates inheritance and polymorphism features into programming and allows code and data to be bound together.

What are the four basics of OOP?

The four essentials of the OOP system are encapsulation, abstraction, polymorphism and inheritance.

What are the three principles of OOP?

The three main fundamental Object-Oriented principles can be pinpointed down to inheritance, encapsulation and polymorphism. These three are undoubtedly the main functions of OOLs or Object-Oriented languages. The ways these principles are implemented depending on the language.

How do you explain polymorphism in interviews?

In OOP, polymorphism can be defined as the ability to implement multiple approaches. There are two main types of polymorphism. Static Polymorphism can be defined as polymorphism that occurs during compiling time while Runtime polymorphism occurs during execution.

What is a real-life example of polymorphism?

One example is using virtual functions in C to effectively print a list of objects that are combined with different functions to return different results. This alongside the outputs of the behaviour of the objects on the list not being specified before runtime is a great real-life example of polymorphism.

What are REST API interview questions?

REST API interview questions are based on the REST architecture and consist of questions about RESTful APIs or how client-server interaction can be seamlessly integrated through REST methodologies.

How to prepare for OOPS coding questions and advanced oops advanced interview questions?

One can easily prepare for OOP questions by revising OOPS concept questions and checking up on more Object-Oriented programming questions from resources and study guides.

What is meant by dynamic polymorphism?

Dynamic polymorphism or dynamic binding is a feature that enables calls to get overridden during runtime instead of during compilation.

What are the limitations of Inheritance?

Inheritance requires much more time to be processed as it navigates through many various classes to be implemented. Another limitation is the base classes and child classes being too tightly bound together, fundamentally requiring nested changes in both the classes when there is a requirement to make a change.

Key Takeaways

OOPs interview questions and answers help candidates prepare for OOPS basic interview questions and instances thrown at them. One must have a good understanding of OOPS concepts for interviews and practise programming in languages such as Java and C++.

OOPs interview questions generally revolve around the important features of OOP and cover OOPS programming questions; thus, one must have a good foundation of OOP for interviews.