Interview Questions and Answers for 'Oop' | Search Interview Question

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Q161. What happens to private variables during inheritance ?

Core Java

Ans. Private variables are not inherited. They are simply ignored and not made part of the derived object body.

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Q162. How can we hide a class in Java ?

Core Java

Ans. By encapsulating it within another class and declaring it private. In such a case, it will only be accessible through parent class or parent class object.

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Very frequently asked. Usually among very first few questions.

Q163. Define encapsulation in Java ?

Core Java

Ans. Encapsulation is a feature of OOP's that binds the data and it's associated methods together as a single unit and facilitate protection and data hiding by providing minimal interface to outside. For example - member variables are declared private and are accessed through public methods. Moreover we have private methods that can only be used internally and hence providing minimal interface to outside class through use of public methods.

Sample Code for encapsulation

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Q164. Give an example of how Object Oriented Programming Concepts can be implemented.

Design

Ans. You can implement encapsulation in Java by keeping the fields (class variables) private and providing public getter and setter methods to each of them. Java Beans are examples of fully encapsulated classes. Encapsulation in Java: Restricts direct access to data members (fields) of a class.

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Q165. What are the different types of loops in Java ?

Core Java

Ans. for, while and do while

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Q166. What is an infinite loop ?

Core Java

Ans. Infinite loop is a programming condition wherein the control goes into an infinite loop because the loop termination condition can never be met. For example -

for(int x=1;x>0;x++){
}

in this loop, with each increment the condition x > 0 will remain true till infinity.

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Q167. Explain Inheritance and Polymorphism.

Core Java

Ans. Getting parent class object properties into child class is called Inheritance.

The process of representing one form into multiple forms is called polymorphism.

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Q168. What is the difference between return and continue statement ?

Core Java

Ans. return is used within a method to return control out of the method. It may be followed by a value which is returned from the method to calling method immediately preceding the point of call.

continue statement is used within a loop to start next iteration without executing the remaining statements in the loop.

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Q169. What are the uses of Abstraction ?

Core Java

Ans. Loose Coupling
Facilitates designing complex applications by making them modular.

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Q170. Which of the OOP's features facilitate dependency injection ?

Design

Ans. Inheritance , Runtime Polymorphism and Composition.

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Q171. Is Runtime Polymorphism possible without Inheritance ?

Core Java

Ans. Yes, Runtime Polymprohism requires either Class inheritance or Interface implementation.

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Q172. Why Java is considered more purer object oriented language than C++ ?

Core Java

Ans. Because of

lack of use of pointers,
Lack of structural programming and
Lack of Multiple Inheritance

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Q173. Why shouldn't we use string concatenation extensively or in a loop ?

Core Java

Ans. Because String being an immutable object creates a new object upon each concatenation cycle. If there is any such need , we should use String Builder whose objects are mutable.

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Q174. how does abstraction help your application ?

Core Java

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Q175. Explain OOps concepts.

Core Java

Ans. There are four main OOP concepts in Java. These are:

Abstraction. Abstraction means using simple things to represent complexity. We all know how to turn the TV on, but we don?t need to know how it works in order to enjoy it. In Java, abstraction means simple things like objects, classes, and variables represent more complex underlying code and data. This is important because it lets avoid repeating the same work multiple times.

Encapsulation. This is the practice of keeping fields within a class private, then providing access to them via public methods. It?s a protective barrier that keeps the data and code safe within the class itself. This way, we can re-use objects like code components or variables without allowing open access to the data system-wide.

Inheritance. This is a special feature of Object Oriented Programming in Java. It lets programmers create new classes that share some of the attributes of existing classes. This lets us build on previous work without reinventing the wheel.

Polymorphism. This Java OOP concept lets programmers use the same word to mean different things in different contexts. One form of polymorphism in Java is method overloading. That?s when different meanings are implied by the code itself. The other form is method overriding. That?s when the different meanings are implied by the values of the supplied variables. See more on this below.

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Q176. What is composition ?

Core Java

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Sample Code for composition

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Q177. What is Overriding ?

Core Java

Ans. Overriding refers to the Methods with same name and parameters, such that the later over rides the former method.

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Q178. What are the characteristics of the object ?

Core Java

Ans. 1. State

Instance variable or member elements forms the object state.

2. Behavior

Member functions forms the object behavior

3. Identity

Every object has a unique identity within JVM through a unique Id.

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Q179. Which of the OOP's feature - encapsulation or abstraction - is more important ?

Core Java

Ans. Encapsulation facilitates security by hiding data and logic whereas Abstraction simplifies organization of data and related logic.

As applications scale, both concepts are required for easy management and maintenance. Encapsulation for security and criss cross communication between objects / modules will make it vulnerable. and Abstraction for better organization that enables better understanding of application code and easy maintainability.

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Q180. Which of the polymorphism type - static or runtime - is more important ?

Core Java

Ans. Method overloading / static polymorphism compared to method overriding / runtime polymorphism has very limited usage as it just opens up an alternate way of defining a different method with the same name.

Method Overriding on other hand opens up many other features like contracting , interfacing , pluging development and hence development of libraries and frameworks.

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Q181. Which of the OOP's feature is most important ?

Core Java

Ans. Encapsulation facilitate hiding and restricted access and hence more of a security feature. Encapsulation is definitely a great feature as when applications expand criss cross communication between objects / modules could lead to blunders.

Inheritance facilitates code reuse.

Polymorphism comprise of method overloaded ( which to me is negligible usage ) and method overriding. Method overriding is of great usage as it facilitates concept of interfaces and plugin development.

So it’s Security / Organization vs

Code Reuse / Support for other features like overriding vs

Contracts / Plugin Development facilitating the creation of frameworks / libraries.

Which is more important may vary from application to application , its scale , its use , its sensitivity etc.

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Q182. How to instantiate jsp variable from another jsp?

JSP

Ans. using session attribute.

session.setAttribute("userId",userId);

in first jsp

int userId=session.getAttribute("userId");

in second jsp;

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Q183. Find unique values between two arrays using single for loop ?

Core Java

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Q184. What is virtual table with respect to method overriding in Java ?

Core Java

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Q185. How is the virtual method table implemented in Java?

Core Java

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Q186. How many VTables are there for each class ?

Core Java

Ans. There is one VTable for each class.

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Q187. Can a class extend itself in Java ?

Core Java

Ans. No

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Q188. Difference between hadoop 1.x and 2.x?

Apache Hadoop

Ans. Hadoop 1.x

It supports only MapReduce (MR) processing model.
It has limited scaling of nodes. Limited to 4000 nodes per cluster.
It has single Namenode to manage the entire namespace.
It has Single-Point-of-Failure (SPOF)
Works on concepts of slots – slots can run either a Map task or a Reduce task
MR has to do both processing and cluster resource management.

Hadoop 2.x

It supports MR as well as other distributed computing models like Spark, Hama, etc
It has better scalability. Scalable up to 10000 nodes per cluster.
Works on concepts of containers. Using containers can run generic tasks.
It has Multiple Namenode servers manage multiple namespace.
YARN does cluster resource management and processing is done using different processing models.

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Q189. Difference between group and cogroup?

Apache Hadoop

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Q190. How Object-Oriented Programming is implemented in JavaScript? How they differ from other languages?

Javascript

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