Top oops interview questions and answers 2023.

Java OOPs Top 50 Interview Questions and Answers in 2023

Java is object oriented and here we are covering oops interview questions and answers. Java inherits features of C++. OOP features of java are influenced by C++. OOP concept forms the heart of java language that helps java program in survive the inevitable changes accompanying software development.

TechShitanshu has prepared a list of the top OOPs interview questions and answers that are frequently asked in the interview. It is going to help you to crack the interview to get your dream job.

Certainly, here are some common oops interview questions that might come up during a job interview. These questions can help the interviewer gauge your qualifications, experience, and fit for the role. Be prepared to answer these questions with confidence:

OOPs Basic Interview Questions

1. Provide a concise definition and explain the key principles of OOP.

Answer: OOP is a way of writing computer programs using objects, which are like building blocks. Objects have data and functions that can work with that data. It’s a way to model real-world things and their interactions in code.

2. How do you create an object in OOP?

Answer: In Object-Oriented Programming (OOP), you create an object by following these steps:

Define a Class: First, you need to define a class. A class is like a blueprint that defines the structure and behavior of objects. It specifies the attributes (data) and methods (functions) that objects created from this class will have.
Instantiate the Class: To create an object, you need to use the class as a template. This is done by instantiating the class, which means you’re creating a specific instance of that class. You do this by calling the class’s constructor method.
Use the Object: Once the object is created, you can use it to access its attributes and methods. You can manipulate the object and perform various operations based on the class’s defined behavior.

3. Describe encapsulation, inheritance, polymorphism, and abstraction.

Answer: Encapsulation is also a part of the OOPs concept. It refers to the bundling of data with the methods that operate on that data. It also helps to restrict any direct access to some of an object’s components.

Inheritance is a feature of OOPs which allows classes inherit common properties from other classes. For example, if there is a class such as ‘vehicle’, other classes like ‘car’, ‘bike’, etc can inherit common properties from the vehicle class. This property helps you get rid of redundant code thereby reducing the overall size of the code.

Polymorphism is one of the most used and core concepts in OOP languages. It explains the concept of different classes can be used with the same interface. Each of these classes can have its own implementation of the interface.

Abstraction is an OOPs concept to build the structure of real-world objects. It “shows” only essential attributes and “hides” unnecessary information from the outside. The main focus of abstraction is to hide unnecessary details from the users. It is one of the most important concepts of OOPs.

4. What are classes and objects in OOP?

Answer: Classes are like blueprints for creating objects. They define the structure and behavior of objects. Objects, on the other hand, are instances of classes, meaning they are actual things created based on those blueprints.

4. Why to use OOPs?

Answer:

Code can be reused through inheritance thereby reducing redundancy
OOPs allows clarity in programming thereby allowing simplicity in solving complex problems
Data and code are bound together by encapsulation
OOPs allows data hiding, therefore, private data is kept confidential
Problems can be divided into different parts making it simple to solve
The concept of polymorphism gives flexibility to the program by allowing the entities to have multiple forms

OOPs Interview Questions for Experienced

1. What is constructor chaining?

Answer: Constructor chaining is a method to call one constructor from another concerning a current object reference. It can be done in two ways: –

Using the “this” keyword, the reference can be made to the constructor in the current class.
To call the constructor from the base class “super” keyword will be used.

2. What are pure virtual functions?

Answer: A popular oops interview questions – A pure virtual function/method is a function whose implementations are not provided in the base class, and only a declaration is provided. The pure virtual function can have its implementation code in the derived class; otherwise, the derived class will also be considered an abstract Class. The Class containing pure virtual functions is abstract.

3. What is the default method of Java 8?

Answer: The default method, also known as the extension method, is a new type of method which you can add to the interface now. These methods have implementation and are intended to be used by default. By using this method, JDK 8 managed to provide common functionality related to lambda expression and stream API without breaking all the clients who implement their interfaces. If you look at Java 8 API documentation you will find several useful default methods on key Java interfaces like Iterator, Map, etc.

4. Can an interface extend more than one interface in Java?

Answer: Yes, an interface can extend more than one interface in Java, it’s perfectly valid.

5. Can a class extend more than one class in Java?

Answer: No, a class can only extend another class because Java doesn’t support multiple inheritances but yes, it can implement multiple interfaces.