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

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Q121. What is the difference between namenode and datanode in Hadoop?

Ans. NameNode stores MetaData (No of Blocks, On Which Rack which DataNode is stored etc) whereas the DataNode stores the actual Data.

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Q122. Can we extend an Enum ?

Core Java

Ans. No. Enums are final by design.

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Q123. Will this code compile ?

public class BuggyBread1{
abstract public void test();
}

Core Java

Ans. No. It will give the compilation error saying "The abstract method test in type BuggyBread1 can only be defined by an abstract class".

We need to declare the class abstract for it to have any abstract method.

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Q124. Is this Polymorphism ?

Map<String, List<String>> inventoryManagerCountMap = new HashMap<String, ArrayList<String>>();

Core Java

Ans. No. This will result in compilation error as Polymorphism cannot be performed on Object types.

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Q125. What is the difference between Data Type and Data Structure ?

Core Java

Ans. Data type: a set of values together with operations on that type
Data structure: a physical implementation of a data type

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Q126. Do you see Class as a Data Type or Data Structure ?

Ans. Class can be better seen as Data Type. This could be implemented as a Data Structure too in some cases.

One thing worth understanding here is that Data type and Data structure are conceptual things. Class could be implementation of either of these.

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Q127. Which of the following is not the difference between Singleton and Static class ( Class with static members only ) ?

a. Only one object can be created for Singleton class whereas No objects are created for static class.
b. Singleton class instance is initiated using new keyword whereas static class instance is created using static method.
c. Singleton class can be serialized whereas Static class cannot be.
d. Singleton Class can participate in runtime Polymorphism whereas Static class cannot.

Ans. Singleton class instance is initiated using new keyword whereas static class instance is created using static method.

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Q128. Which is the default Input Formats defined in Hadoop ?

a. SequenceFileInputFormat
b. ByteInputFormat
c. KeyValueInputFormat
d. TextInputFormat

Ans. TextInputFormat

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Q129. Which of the following is not an input format in Hadoop ?

a. TextInputFormat
b. ByteInputFormat
c. SequenceFileInputFormat
d. KeyValueInputFormat

Ans. ByteInputFormat

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Q130. Which of the following is a valid flow in Hadoop ?

a. Input -> Reducer -> Mapper -> Combiner -> -> Output
b. Input -> Mapper -> Reducer -> Combiner -> Output
c. Input -> Mapper -> Combiner -> Reducer -> Output
d. Input -> Reducer -> Combiner -> Mapper -> Output

Ans. Input -> Mapper -> Combiner -> Reducer -> Output

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Q131. MapReduce was devised by ...

a. Apple
b. Google
c. Microsoft
d. Samsung

Ans. Google

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Q132. Which of the following is not a phase of Reducer ?

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

Ans. Map

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Q133. 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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Q134. 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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Q135. 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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Q136. 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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Q137. 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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Q138. 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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Q139. 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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Q140. 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.

Q141. 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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Q142. 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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Q143. 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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Q144. What are the two main components of Hadoop System ?

BigData

Ans. Distributed file system and Map Reduce system.

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Q145. 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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Q146. 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.

Q147. What are the principle concepts of Object Oriented Programming ?

Core Java

Ans. Abstraction Polymorphism Inheritance Encapsulation

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Q148. 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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Q149. 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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Q150. 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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