Most Common OOPS Interview Questions & Answers

OOPS is one of the most popular programming languages. Therefore, if you have applied for the position of software developer or programmer, there is a high chance that the interviewer might ask you some questions related to OOPS. Therefore, it is necessary to know about OOPS.

Most Common OOPS Questions and Answers

1. What is OOPS?

OOPS is the object-oriented programming system in Java that uses object methodology. These objects contain information and a code and have unique characteristics. Instead of using functions or logic, OOPS uses classes and objects to design a program. It increases the scalability of the program.

2. What are the main features of OOPS?

There are five main features of object-oriented programming; 

• Classes:- A class is the vital component of the building block of an OOP language. These classes segregate objects with similar features and make it easier for the developer to understand the objects.
• Objects:- These are entities with specific characters or behavior that hold some special information for the developer. They are enclosed within a class.
• Inheritance:- It means adding the already existing properties or attributes of a particular class to another class.
• Polymorphism:- This feature is used to give poly or a variety of meanings to a single object or variable in programming. This is to understand the meaning of the objects in different circumstances.
• Data Abstraction and Encapsulation:- The two most significant features of OOPS are data abstraction and encapsulation. While the concepts can seem similar, there are some differences between them. Encapsulation refers to the process of hiding information from other users. It is useful when multiple people work on the same product. On the other hand, abstraction is the process that shows only relevant features or characteristics of objects within a particular class.

3. What are the advantages of OOPS?

OOPS offers several advantages:

• Class in OOPS facilitates reusability. Programmers can use the same facilities multiple times rather than building a new facility every time.
• Data encapsulation and abstraction in object-oriented languages make it secure. It does not allow people to see restricted information.
• OOPS allows modification to codes without any hassle. Therefore, it allows for easy maintenance.
• OOPS languages are excellent for problem-solving as we can define a class for each problem.
• OOPS also allows easy troubleshooting through the encapsulation feature.

4. Explain the limitations of OOPs.

OOPS is not a universal language and has certain limitations:

• Excess scalability can be an issue in OOPS. If left unchecked, it can create lengthy codes. Therefore, sometimes programmers may write lengthy codes than what is required.
• Excellent designing and programming skills are a must for OOPS otherwise, it can be tricky to understand the language.
• Since OOPS programs require more levels of execution, they are slow compared to procedural programming platforms.
• We cannot use OOPS for programs that require functional, logic, or procedure-based programming.

5. Explain the difference between object-oriented programming and procedural programming.

• Object-oriented programming uses the concept of objects for building a programming model. Procedural programming, on the other hand, procedural programming uses routines or procedures for executing the program.
• Procedural programming uses a top-down approach, whereas object-oriented programming uses a bottom-up approach.
• In procedural programming, the data can move freely between functions, whereas in object-oriented programming, the objects communicate via functions.
• There is no concept of inheritance in procedural programming, whereas inheritance is a core feature in OOP. 

6. Why is Java not a pure OOPS language?

Pure object-oriented programming languages use objects as their base. They do not support primitive data types like char, int, or float. Pure OOPS languages have features like inheritance, encapsulation, and abstraction. Java is not a pure object-oriented programming language as it uses primitive data types like int, char, ex, float as the objects. Moreover, pure OOP languages do not have static keywords. They pass a message for every action.

7. What are virtual and friend functions?

A member function declared within the base class is called a virtual function. It is overridden by or redefined by a derived class. We usually use virtual functions for runtime polymorphism. These functions are accessed through a reference of a base class or a pointer. For example, friend functions in OOPS are the functions of such a class that is outside the scope of the class but can still access the private and protected members of that class.

8. What are the different types of inheritance in OOPS?

There are mainly five different types of inheritance in OOPS.

• Single Inheritance:- When a single child class inherits the properties of a single parent class, it is called single inheritance.
• Multiple Inheritance:- When a single class inherits features of more than one parent class, it is called multiple inheritances. Java does not support multiple inheritances.
• Multilevel Inheritance:- When a class inherits features from another class that has also inherited the attributes of a third class, it is called multilevel inheritance.
• Hybrid Inheritance:- When single and multiple inheritances combine in a function, it is called hybrid inheritance.
• Hierarchical Inheritance:- When one class passes its features to multiple subclasses, it is called hierarchical inheritance.

9. What is abstraction?

The purpose of abstraction in OOPS is to hide irrelevant or unnecessary features from the client. It focuses only on the essential parts. For example, when you place an order on an eCommerce website, the shipment is connected through different cities and packages till it finally reaches you. While placing the order, you do not see through which cities your package will arrive. All we are concerned with is the expected delivery date of the shipment. The logistics details are unnecessary. This is what we call abstraction. 

10. Explain exception and exceptional handling in OOPS.

The notifications that interrupt the normal executions of functions are called exceptions. Exceptions are used to process errors in OOPS. They arise when there is a problem in the program, and the function cannot be executed. Exceptional handling is a process through which runtime errors are handled in OOPS.

11. Explain Static Binding and Dynamic Binding.

Binding is an association of methods in OOPS. When the programmer determines the objects and maps the method during compilation time, we term it static binding or early binding. Usually, static, private, and final methods are mapped using static binding to prevent overriding them during the runtime.

On the contrary, dynamic binding occurs when the developer maps the method while executing the program. Dynamic binding is usually done in method overriding.

• Static binding does not use an actual object for binding, whereas, in dynamic binding, we use the actual object.
• Static binding involves method overloading, whereas dynamic binding involves overriding methods. 

12. What is aggregation?

Aggregation brings together or relates two or more independent objects having different owners. We need aggregation in OOPS to reuse the same classes multiple times in the program.

13. What is a constructor?

We can understand a constructor as a special member of a class whose purpose is to initialize the objects of a class. It does not have a return type. They have the same name as a class, and the program automatically calls a constructor when the programmer creates an object. We need to place a constructor in the public section of a class.

14. Explain the difference between interface and abstract class.

We use both abstract class and interface to declare abstract methods. However, both are different concepts. 

• While an abstract class allows abstract and non-abstract methods, the interface only allows abstract methods.
• While an abstract class can extend multiple Java interfaces, the interface extends a single Java interface.
• We can have private or protected members in an abstract class. But the objects in the interface are public.
• While the interface allows multiple inheritances, we can expect only one inheritance from an abstract class.

Conclusion

Object-oriented programming languages are an integral part of software engineering development. You must know all about OOPS if you want to become a software developer or engineer. To learn OOPS in-depth, you can pursue the Executive PG Program in Software Development through upGrad. The program offers you a specialization in full-stack development. During the two weeks preparatory course, you will learn the fundamentals of programming language with basic data structures. You will also be taught the practical usage of various tools and programming languages like Python, Java, Hadoop, GIT, and Burpsuite.

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