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Q151. Why do you want to leave your current job ?

Ans. The most effective and acceptable reasons for leaving your current job should be positive e.g. moving forward in your life or career

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Q152. Explain Java collections

Core Java

Ans. Collection is a container which is used to store and manipulate the group of objects

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Q153. Have you ever built an automation suite to test a cron job or command line application ?

Testing

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Q154. What is your role in current project ?

General

Ans. Possible Answer - Java Developer

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Q155. Difference between Arrays and LinkedList ?

Data Structure

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Q156. Why do we need to close the Scanner ?

Core Java

Ans. For releasing input stream reference (System.in), you should close scanner.

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Q157. What will the following code return

list.stream().collect(Collectors.groupingBy(ClassA::getElement1,
Collectors.averagingDouble(ClassA::getElement2)));

Core Java

Ans. Map<DataType1,DataType2> where DataType1 is the data type of element1 ( returned by getelement1 method ) and DataType2 is the data type of element2 ( returned by getElement2 method )

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Q158. What are we doing here

list.stream().collect(Collectors.groupingBy(ClassA::getElement1,
Collectors.averagingDouble(ClassA::getelement2)));

Core Java

Ans. We are averaging elements of a collection by element1 grouped by element1

* list is the reference of collection
* element1 is the member element returned by getElement1 method of ClassA
* element2 is the member element returned by getElement2 method of ClassA

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Q159. Can you explain following exception

java.lang.ArithmeticException: Non-terminating decimal expansion; no exact representable decimal result.

Core Java

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Q160. How Reflection can break any design pattern ?

Design

Ans. Using java reflection api, we can tweak into a class and modify it's runtime behavior and hence modify the pattern it might be using.

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Q161. What is a weak reference ?

Core Java

Ans. A weak reference is a reference that gets removed on the next garbage collection cycle.

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Q162. What will the following code print and Why

class Class1 {
static{
System.out.println("Wow");
}
public static final int xyz=1;
}

class Class2{
public static void main(String[] args) {
System.out.println(String.valueOf(Class1.xyz));
}
}

Core Java

Ans. 1

Reason being that Class1.xyz is replaced with 1 during pre compilation only and a reference to Class1 is never made.

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Q163. Which are the thread safe / synchronized / concurrent classes in java collections ?

Core Java

Ans. Stack
Properties
Vector
BlockingQueue
ConcurrentMap
ConcurrentNavigableMap

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Q164. Write code for serialization.

Core Java

Ans. // Java code for serialization and deserialization
// of a Java object
import java.io.*;

class Demo implements java.io.Serializable
{
   public int a;
   public String b;

   // Default constructor
   public Demo(int a, String b)
   {
      this.a = a;
      this.b = b;
   }

}

class Test
{
   public static void main(String[] args)
   {
      Demo object = new Demo(1, "geeksforgeeks");
      String filename = "file.ser";

      // Serialization
      try
      {
         //Saving of object in a file
         FileOutputStream file = new FileOutputStream(filename);
         ObjectOutputStream out = new ObjectOutputStream(file);

         // Method for serialization of object
         out.writeObject(object);

         out.close();
         file.close();

         System.out.println("Object has been serialized");

      }

      catch(IOException ex)
      {
         System.out.println("IOException is caught");
      }

      Demo object1 = null;

      // Deserialization
      try
      {
         // Reading the object from a file
         FileInputStream file = new FileInputStream(filename);
         ObjectInputStream in = new ObjectInputStream(file);

         // Method for deserialization of object
         object1 = (Demo)in.readObject();

         in.close();
         file.close();

         System.out.println("Object has been deserialized ");
         System.out.println("a = " object1.a);
         System.out.println("b = " object1.b);
      }

      catch(IOException ex)
      {
         System.out.println("IOException is caught");
      }

      catch(ClassNotFoundException ex)
      {
         System.out.println("ClassNotFoundException is caught");
      }

   }
}

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Q165. What is Web Server and explain its types?

Server

Ans. A program that uses HTTP for serving files that create web pages for users in response to their requests that are sent by the HTTP clients of their computer is called as a web server.

Web - Server Types

Apache HTTP Server by the Apache Software Foundation
Internet Information Service from Microsoft
Sun Java System Web Server
Jigsaw Server.

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Q166. Explain Binary Search

Algorithm

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Q167. How can we make objects if the constructor is private ?

Core Java

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Q168. Can we modify a list while iterating it ?

Core Java

Ans. No,we cannot.I t will give concurrentModificationExceptin error. It can be resolved by using ConcurrentClasses like ConcurrentHashMap,CopyOnWriteArrayList,BlockingQueue etc which are fail-safe and wont give exception.

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Q169. When do you use a Vector?

Core Java

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Q170. How do you define a functional interface?

Core Java

Ans. Create interface with the only one non-overriding abstract method and annotate it with @FunctionalInterface

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Q171. Can you give a real life example of synchronization

Core Java

Ans. Intersection with traffic light

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Q172. In the Following code which foo will get called.

foo(Integer i){
}

foo(String s){
}

public static void main(){
passing foo(null);
}

Core Java

Ans. ambiguity error

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Q173. What is composition ?

Core Java

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Sample Code for composition

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Q174. How cloud computing is different than virtualization ?

Server

Ans. A Virtualization is software that virtualizes your hardware into multiple machines while Cloud computing is the combination of multiple hardware devices. In Virtualization, a user gets dedicated hardware while in Cloud computing multiple hardware devices provide one login environment for the user.

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Q175. What are the benefits of cloud computing ?

Server

Ans. Primary benefits of cloud computing include –

Data backup and storage
Reduced costs of managing and maintaining IT systems
Powerful server capability and scalability
Better productivity and collaboration efficiency
Access to automatic updates

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Q176. What are the reasons to choose between reserved and on demand instances ?

Server

Ans. In terms of compute options and configurations, Reserved Instances and On Demand instances are the same. The only difference between the two is that a Reserved Instance is one you rent (reserved) for a fixed duration, and in return you receive a discount on the base price of an On Demand instance.

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Q177. What is an applet ?

Java EE

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Q178. Which collection stores element in insertion order ?

Core Java

Ans. LinkedList maintains the insertion order in collection.

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Q179. What is collection framework in Java ?

Core Java

Ans. The Java collections framework (JCF) is a set of classes and interfaces that implement commonly reusable collection data structures. Although referred to as a framework, it works in a manner of a library. The JCF provides both interfaces that define various collections and classes that implement them.

Sample Code for Map

Sample Code for HashMap

Sample Code for Treemap

Sample Code for set

Sample Code for hashset

Sample Code for treeset

Sample Code for list

Sample Code for arraylist

Sample Code for linkedlist

Sample Code for queue

Sample Code for priorityqueue

Sample Code for concurrenthashmap

Sample Code for vector

Sample Code for stack

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Q180. how does abstraction help your application ?

Core Java

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