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Q1261. What is the POM packaging in Maven ?

Ans. pom packaging is simply a specification that states the primary artifact is not a war or jar, but the pom.xml itself.

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Q1262. Difference between Maven Project and Module ?

Maven

Ans. Maven Module has a Parent whereas Project doesnt. when we add the parent section to the pom file, it adds the module section to the parent project pom file. When we execute mvn compile / install, it basically checks that module section of the parent to identify all the modules that needs to be compiled first.

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Q1263. What is meant by following error ?

Source folder is not on the Java build class path

Core Java

Ans. It means that the respective folder is not looked upon by Java to look for java or resource files and hence not being included as part of build.It needs to be added to Java Build Path.

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Q1264. How Java is different than C/C++ in terms of memory allocation and de-allocation ?

Core Java

Ans. Java provides a faster allocation mechanism but at the cost of expensive deallocation. Deallocation in java is done by mechanism called garbage collection that runs periodically to free up unclaimed memory space , which actually slows down the application. Hence Java is usually faster if memory is not of concern and sufficiently large memory can be allocated to an application.

C/C++ on other hand have equal cost of allocation and de-allocation.

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Q1265. What is a shutdown hook ?

Core Java

Ans. Shutdown hook is a thread that is invoked implicitly by JVM just before the shut down. It is used to clean up unused resources.

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Q1266. Can we start the same thread twice ?

Core Java

Ans. No we cannot start the same thread twice. Each thread has a lifecycle.

But Yes, we can run the same code in parallel using different threads.

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Q1267. Write an Algorithm for Graph Traversal ? The Graph has a loop.

Algorithm

Ans. Please not that all such questions can be easily answered through recursion.

Simple recursive implementation could be

traverse(root);

void traverse(Element element){
if(element.hasNext()){
traverse(element.next());
} else {
System.out.println(element);
}
}

but this algo / code lead to endless loop if there is a loop in graph traversal.

So you can keep a collection to keep track of which elements have laready been traversed

static List<Elements> listOfAlreadyTraversedElements = new ArrayList<Elements>();

main(){
traverse(root);
}

void traverse(Element element){
if(element.hasNext()){
traverse(element.next());
} else {
listOfAlreadyTraversedElements.add(element);
System.out.println(element);
}
}

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Q1268. How is String class unique ?

Core Java

Ans. String class is immutable as well as final. Because of these properties , String objects offer many benefits

1. String Pool - When a string is created and if it exists in the pool, the reference of the existing string will be returned instead of creating a new object. If string is not immutable, changing the string with one reference will lead to the wrong value for the other references.

Example -

String str1 = "String1";
String str2 = "String1"; // It doesnt create a new String and rather reuses the string literal from pool

// Now both str1 and str2 pointing to same string object in pool, changing str1 will change it for str2 too

2. To Cache its Hashcode - If string is not immutable, One can change its hashcode and hence its not fit to be cached.

3. Security - String is widely used as parameter for many java classes, e.g. network connection, opening files, etc. Making it mutable might possess threats due to interception by the other code segment.

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Q1269. Explain Agile Software Development Methodology ?

Process

Ans. https://en.wikipedia.org/wiki/Agile_software_development

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Q1270. What is the most used Java Class ?

Core Java

Ans. Object class as its the parent class of all Java classes.

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Q1271. How would you count the number of words in a string consisting of uneven number of spaces between words( not dictionary words)? With and without library functions.

Core Java

Ans. package com.string;

import java.util.Scanner;

public class String13 {
public static void main(String[] args) {
System.out.println("Enter Sentence");
Scanner sc=new Scanner(System.in);
String sentence=sc.nextLine();
String[] words=sentence.split(" ");
int count=0;
for (String string : words) {
string.trim();
if(!string.equals("")){
count++;
System.out.println(string " " count);
}
}
}
}

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Q1272. How to specify the sequence in which sub modules needs to be built ?

Maven

Ans. By specifying the modules in the same sequence in the parent pom.

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Q1273. How to perform Maven Build and show Debug Information ?

Maven

Ans. Use -X option

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Q1274. Difference between JDBC and Hibernate ?

Database

Ans. JDBC is a standard Java Api for Database communication whereas Hibernate is an ORM framework that uses JDBC to connect with Database.

Hibernate is another layer of object table mapping over JDBC that provide a database independent, object oriented and an efficient way of database communication.

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Q1275. Have you ever tried mocking static methods ?

Testing

Ans. Yes, that can be done using Power Mock. Mockito doesnt provide a way to mock static methods.

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Frequently asked in Alibaba (Based on 2 feedback)

Q1276. What is the best Memory setting for JVM ?

Core Java

Ans. In Java JVM memory settings is done by use the arguments -Xms -Xmx. Use M or G after the numbers for indicating Megs and Gigs of bytes respectively. -Xms indicates the minimum and -Xmx the maximum.

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Q1277. Design an online shopping site system ?

Design

Ans. AWS Services - CloudFront for distribution / caching, EC2 for computing, EBS for block storage , S3 for object storage , RDS for database , Kinesis for streaming , CloudWatch for monitoring.

Technologies - Java for back end with Spring Boot , Angular , RxJs for front end .

Architecture - Service Oriented. Multi layer.

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Q1278. Difference between relational databases and NoSQL databases ?

Database

Ans. https://www.mongodb.com/scale/nosql-vs-relational-databases

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Q1279. How would you process a 20 gb file with an application only having access to 4gb memory ?

BigData

Ans. Load the file in chunks and then process. If we need to do analytic, we can process analytic information for those chunks and then reprocess the processed information from each chunk.

For example - we need to average all marks in the file. We can divide the file and load into 5 chunks and calculate average for each chunk. Then we can collect averages for all 5 chunks and then calculate the final average.

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Q1280. What is a web service ?

Java EE

Ans. A Web service is a service offered by one system to another, for communication over web through http. XML are JSON are usually used for sending across information from one system to another.

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Q1281. Write Delegate function of JQuery ?

JQuery

Ans. http://www.w3schools.com/jquery/event_delegate.asp

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Q1282. What is the difference between http and https ?

Java EE

Ans. https encrypts the data using SSL whereas http sends it as plain text, So https is secure protocol whereas http is not.

Moreover https connects on port 443, while HTTP is on port 80

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Q1283. Implement an LRU Cache ?

Design

Ans. https://www.programcreek.com/2013/03/leetcode-lru-cache-java/

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Q1284. Flatten a Binary Tree to Linked List

Algorithm

Ans. https://www.geeksforgeeks.org/flatten-a-binary-tree-into-linked-list/

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Q1285. How to delete duplicate elements in a table ?

Database

Ans. DELETE FROM TABLE WHERE ROW_NUM NOT IN ( SELECT MAX(ROW_ID) FROM TABLE GROUP BY DUPLICATE_FIELD )

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Q1286. Write a Program to print permutations of a String.

Core Java

Ans. public static Stream permutations(String str) {
if (str.isEmpty()) {
return Stream.of("");
}

return IntStream.range(0, str.length()).boxed()
.flatMap(i -> permutations(str.substring(0, i) str.substring(i 1)).map(t -> str.charAt(i) t));

}

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Q1287. How to create stateful Rest Services ?

Rest

Ans. There is no direct way to make stateful REST service but when first time request send to server, generate the token on server and send back to client. When every time new request is send the token is send to identify the request is coming from same client.

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Q1288. Difference between Array and ArrayList ?

Core Java

Ans. <a href="http://javahungry.blogspot.com/2015/03/difference-between-array-and-arraylist-in-java-example.html" rel="nofollow">http://javahungry.blogspot.com/2015/03/difference-between-array-and-arraylist-in-java-example.html</a>

Sample Code for ArrayList

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Q1289. Difference between Error and Exception ?

Core Java

Ans. An Error indicates serious problems that a reasonable application should not try to catch whereas

An Exception indicates conditions that a reasonable application might want to catch.

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Frequently asked in Accenture.

Q1290. What is your biggest achievement at work ?

General

Ans. [Open Ended Answer]

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