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

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Q131. Which of the following is not a phase of Reducer ?

a. Map
b. Reduce
c. Shuffle
d. Sort

Ans. Map

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Q132. How many instances of Job tracker can run on Hadoop cluster ?
a. 1
b. 2
c. 3
d. 4

Ans. 1

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Q133. Which of the following is not the Dameon process that runs on a hadoop cluster ?

a. JobTracker
b. DataNode
c. TaskTracker
d. TaskNode

Ans. TaskNode

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Q134. What is an instance variable?

a. An instance or object of an class
b. The field of an object
c. Any variable of a class
d. None of the above

Ans. The field of an object

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Q135. Which of the following do you think is the primary reason you would never use a static class even the application doesn't need multiple requests or threads ?

a. Serialization
b. Runtime Polymorphism
c. Lazy Loading
d. Memory

Ans. Runtime Polymorphism

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Q136. What is a Sequence File?

a. A Sequence File contains a binary encoding of an arbitrary number of homogeneous writable objects.
b. A Sequence File contains a binary encoding of an arbitrary number key-value pairs. Each key must be the same type. Each value must be of same type.
c. A Sequence File contains a binary encoding of an arbitrary number of heterogeneous writeable objects.
d. A Sequence File contains a binary encoding of an arbitrary number of Writable Comparable objects, in sorted order.

Ans. A Sequence File contains a binary encoding of an arbitrary number key-value pairs. Each key must be the same type. Each value must be of same type.

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Q137. What is the input to the Reduce function ?

a. One Key and One Value
b. Multiple Keys and Multiple associated Values
c. Multiple Keys and One associated values with each
d. One key and associated values.

Ans. One key and associated values.

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Q138. Which of the following is the implementation language for Map Reduce Framework ?

a. Big Data
b. Hadoop
c. Java
d. C++

Ans. Java

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Q139. Will a for loop like following throw a compilation error ? for(;;);

Ans. No. It will result in infinite loop

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Must know at all levels. Among Top 10 frequently asked questions in Java. Very frequently asked to fresh graduates or less experienced professionals.

Q140. What is Inheritance ?

Core Java

Ans. Its a facility for code reuse and independent extension wherein a derived class inherits the properties of parent class.

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Q141. How is static and dynamic polymorphism achieved in Java ?

Core Java

Ans. Static polymorphism is the polymorphic resolution identified at compile time and is achieved through function overloading whereas dynamic polymorphism is the polymorphic resolution identified at runtime and is achieved through method overriding.

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Q142. How is multiple inheritance implemented in Java ?

Core Java

Ans. There was no multiple inheritance in java before version 8 as implementing multiple interfaces cannot be termed as inheritance.

With Java 8 , came the concept of default methods wherein the class implementing the interface carries the default implementation from the interface and hence facilitating multiple inheritance.

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Q143. What are the two main components of Hadoop System ?

BigData

Ans. Distributed file system and Map Reduce system.

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Q144. What is Hadoop Framework ?

BigData

Ans. Hadoop is an open source framework , written in java by apche software foundation. This framework is used to write applications to process vast amount of data. Processing happens in parallel on large clusters which could have 1000 of computers. It processes data in a very reliable and fault tolerant manner.

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Q145. What is the use of Combiners ?

BigData

Ans. Combiners are used to increase the efficiency of a Map Reduce program. They are used to aggregate intermediate map output locally on individual mapper outputs. Combiners can help you reduce the amount of data that needs to be transferred across to the reducers.

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Very Frequently asked to fresh graduates and less experienced.

Q146. What are the principle concepts of Object Oriented Programming ?

Core Java

Ans. Abstraction Polymorphism Inheritance Encapsulation

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Q147. What is multilevel inheritance ?

Core Java

Ans. Multi Level Inheritance is multi level hierarchy of classes. Here is the example - http://www.buggybread.com/2015/09/java-se-class-diagram-classes-that_603.html

Class RoleList extends ArrayList which in turn extends AbstractList which in turn extends AbstractCollection.

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Q148. Does default methods introduce multiple inheritance and the Diamond problem in Java 8 ?

Core Java

Ans. Default methods results in multiple inheritance of behavior and not of state. In case we try to implement multiple interfaces with default method having same name and signature, and don't override it in implementation class, it will throw an error.

For example -

interface MyInterface {
public void default myMethod(){
}
}

interface MyInterface2 {
public void default myMethod(){
}
}

class MyClass implements MyInterface,MyInterface2 {
}

This code will compilation error "Duplicate Default Method"

if we specify the definition of myMethod() in myClass, compiler won't complain and there is no conflict and MyClass can use overridden definition. But if we don't override myMethod() in MyClass, Java would be in conflict as to what definition should be carried to MyClass and hence throws compilation error.

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Q149. Can we access private members of the parent class ? i.e Are private members of the class visible in the derived class ?

Core Java

Ans. No, If both Parent and Derived are outer classes.

public class Vehicle {
private static String manufacturingDate = "2016";
}

public class Car extends Vehicle{
public static void main(String args[]){
System.out.println(manufacturingDate); // error - The field Vehicle.manufacturingDate is not visible
}
}

Yes, If derived is the inner class of Parent.

public class Vehicle {
private static String manufacturingDate = "2016";
static public class Car extends Vehicle{
public static void main(String args[]){
System.out.println(manufacturingDate); // no problem
}
}
}

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Q150. Difference between multiple and multi level inheritance ?

Core Java

Ans. Multiple Inheritance refers to the concept of a class inheriting multiple classes. Example - Class C extends Class A ,Class B. This is not allowed in Java.

Multilevel Inheritance refers to the concept of Inheritance in a chain. Example - Class B extends Class A, Class C extends Class B. This is permitted in Java.

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Q151. Can you name some of the Java frameworks in different domains ?

Frameworks

Ans. Web Framework - Spring , Struts, Play
Dependency Injection frameworks - Google Guice , PicoContainer and Dagger
ORM Framework - Hibernate
Big Data / ETL Frameworks - Apche Hadoop , Apache Crunch, Apache Spark.
View Frameworks - JSF , Apache Wicket,jtwig.
Java Gui Frameworks - SWT , AWT, JavaFX
Testing - Junit, Mockito, PowerMock, EasyMock, JMock, JMockit
Rest Web services - Jersey , Restlet , RestX, RestEasy ,Restfulie

Here is the big list for reference - http://javasearch.buggybread.com/home2.php?keyword=

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Q152. What are the core OOPs concepts ?

Core Java

Ans. Abstraction, Encapsulation, Polymorphism , Composition and Inheritance

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Q153. How are the concept of Association related to Composition and Inheritance ?

Core Java

Ans. Composition and Inheritance are the different types of Associations for Classes.

Composition is a has-a association between classes.
Inheritance is a is-a association between classes.

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Q154. how many reducer task runs on a hadoop cluster ?

BigData

Ans. Generally one reducer runs for all mappers, but it can be increased as per requirements.

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Q155. Is it a good design practice to have programming constructs like if and loops in constructor ?

Design

Ans. I would avoid that. If we need to initialize member elements differently on the basis of some condition, I would prefer having overloaded constructors. I don't see a need to have a loop for initializing member elements unless the count of elements is huge and they all need to be initialized with common value.

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Q156. What are the counter controlled repetitions in java ?

Core Java

Ans. Counter controlled repetitions are the loops that are controlled with the use of counters or the loops where the number of repetitions are known in advance. for loop in java is the counter controlled repetition.

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Q157. Which of the two - compile time and run time polymorphism - requires signature of the method to be different ?

Core Java

Ans. runtime polymorphism or method overriding doesn't require method name and signature to be different whereas compile time polymorphism or method overloading requires method name to be same but the signature to be different.

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Q158. What is "dynamic method dispatch" in java ?

Core Java

Ans. dynamic method dispatch is a process in which a call to an
overridden method is resolved at runtime rather than at compile-time. This is used to achieve runtime polymorphism in java.

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Q159. How do you take screenshot in selenium?

Selenium

Ans. TakeScreenshot th = TakeScreenshot(driver); //Enable the driver object to take screenshot

File src = th.getScreenShotAs(OutputType.FILE);

FileUtils.copyFilesrc("locationWhereUWantToPlaceTheScreenshot.jpg");

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Q160. What is dynamic dispatch in Java ?

Core Java

Ans. Dynamic dispatch in java is also known as runtime polymorphism.It is a process in which a call to an overriden method is resolved at runtime.

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