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Interview Questions and Answers - Order By Rating

   
  Q271. Difference between jar , war and ear ?Java EE
Ans. Jar is Java Archieve i.e compressed Class or Class / Java files.

War comprises of compressed Servlet class files,JSP FIles,supporting files, GIF and HTML files.

Ear comprise of compressed Java and web module files ( was files ).

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   Like         Discuss         Correct / Improve     java   j2ee   jar   web development   war   ear   build management   release management     Asked in 12 Companies      basic        frequent

  Q272. What is Jenkins ?Jenkins
Ans. It is a continuous integration tool written in Java.

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   Like         Discuss         Correct / Improve     java   jenkins     Asked in 6 Companies      Basic        frequent

Very Frequently asked. Have been asked in HCL Technologies very frequently ( based on 3 feedback ). Among first few questions in many interviews.
  Q273. Differences between abstract class and interface ?Core Java
Ans. Abstract classes can have both abstract methods ( method declarations ) as well as concrete methods ( inherited to the derived classes ) whereas Interfaces can only have abstract methods ( method declarations ).

A class can extend single abstract class whereas it can implement multiple interfaces.

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   Like         Discuss         Correct / Improve     java   classes   abstract class   interfaces   abstract class vs interface   abstract classes vs interfaces     Asked in 82 Companies      basic        frequent

 Q274. Which takes more memory - float or Float ?Core Java
Ans. float is a native data type whereas Float is a class. A Float object will always take more memory than float variable as there are metadata overheads with the objects.

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   Like         Discuss         Correct / Improve     java   data type   float     Asked in 3 Companies      basic        frequent

 Q275. Difference between Stack and Heap memory ?Core Java
Ans. Stack memory areas is used to hold method and local variables while objects are always allocated memory in the heap. The heap memory is shared between multiple threads whereas Stack memory isn't.

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   Like         Discuss         Correct / Improve     java   memory management   stack memory   heap memory   difference between   ebay     Asked in 2 Companies      intermediate        frequent
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 Q276. What is collision in hash collections ?Core Java
Ans. Collision is the situation when two different elements have the same Hash Code.

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   Like         Discuss         Correct / Improve     java   collections   collision   hashcode  hash code   hash collections   ebay     Asked in 1 Companies      intermediate        frequent

 Q277. Which of the collections allows null as the key ?

a. HashTable
b. HashMap
c. TreeMap
d. LinkedHashMap		Core Java
Ans. HashMap

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   Like         Discuss         Correct / Improve     java   collections   map  hashtable     Asked in 2 Companies      basic        frequent

  Q278. Explain Application / Server architecture being used in your project ?

or

Explain your project architecture ?
Ans. We are using cluster of Web servers and Application servers. Load Balancer is used to manage the load between them. Down the layer we have middleware server and then DB server to access database.

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   Like         Discuss         Correct / Improve     architecture   production support   java   servers   application support     Asked in 7 Companies        frequent

 Q279. Difference between prefix and postfix increment operator ?
Ans. Prefix operator performs the increment and then assignment whereas its inverse for postfix operator.

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   Like         Discuss         Correct / Improve     prefix increment operator   postfix increment operator   operators   java      basic        frequent

 Q280. Which java frameworks have you used ?General
Ans. I have primarily worked on Web applications and hence worked on Struts , Spring , Hibernate, JSF ( Java Server Faces ) , Velocity etc.

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   Like         Discuss         Correct / Improve     elsevier   frameworks   java frameworks   general question     Asked in 3 Companies      basic        frequent

Almost sure to be asked in every company using any Dependency Injection framework ( Spring, Guice etc )
  Q281. What is Dependency Injection or IOC ( Inversion of Control ) ?Design
Ans. It is a Design Pattern that facilitates loose coupling by sending the dependency information ( object references of dependent object ) while building the state of the object. Objects are designed in a manner where they receive instances of the objects from other pieces of code, instead of constructing them internally and hence provide better flexibility.

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   Like         Discuss         Correct / Improve     design patterns   ioc ( Inversion of Control )  dependency injection     Asked in 83 Companies      intermediate        frequent

  Q282. Explain the challenging problems you faced recently and how you overcame it ?General
Ans. [Open Ended Answer]

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   Like         Discuss         Correct / Improve     elsevier   open ended questions   overstock.com   cerner     Asked in 15 Companies        frequent

 Q283. Explain TDD or Test Driven Design ?Design
Ans. TDD is a development process that involves short iterations: first an automated test case is written. Then, the code is written to pass that test, and finally one refactors the new code to acceptable standards.

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   Like         Discuss         Correct / Improve     elsevier   test driven design ( TDD )   software development methodologies     Asked in 3 Companies        frequent

Frequently asked in face to face interviews.
  Q284. Write a program to print fibonacci series.Core Java
Ans. int count = 15;
int[] fibonacci = new int[count];
fibonacci[0] = 0;
fibonacci[1] = 1;
for(int x=2; x < count; x++){
fibonacci[x] = fibonacci[x-1] + fibonacci[x-2];
}

for(int x=0; x< count; x++){
System.out.print(fibonacci[x] + " ");
}

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   Like         Discuss         Correct / Improve     ebay   fibonacci series     Asked in 66 Companies      basic        frequent

  Q285. How are values passed in Java ? By value or reference ?Core Java
Ans. Java only provides pass by value.

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   Like         Discuss         Correct / Improve     ebay   pass by value   pass by reference   method call   methods   functions   function call     Asked in 10 Companies      basic        frequent

 Q286. What is the use of Synchronized block ?Core Java
Ans. The goal of a synchronised block is to achieve mutual exclusion i.e at one time, the segment of the code should be executed by single thread only and hence the lock needs to be retrieved before executing the segment and then released.

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   Like         Discuss         Correct / Improve     synchronized block   synchronized   synchronization   multithreading   threads   mutual exclusion   concurrency     Asked in 4 Companies      intermediate        frequent
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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.
  Q287. 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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   Like         Discuss         Correct / Improve     inheritance  object oriented programming (oops)  oops concepts  oops concepts  java concepts  code reuse  code re-use   classes  derived classes     Asked in 14 Companies      basic        frequent

 Q288. What is a Java Bean ? How is it different from other Java classes ?
Ans. A Java bean is a class which abides by following conventions:

Core of the object is member elements and not operations ( methods )

Member Elements can be accessed by getters (and setters if those properties are not read-only).

serializable.

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   Like         Discuss         Correct / Improve     java bean   javabean   pojo   classes      basic        frequent

 Q289. Write code for singleton classDesign
Ans. http://javasearch.buggybread.com/CodeSnippets/searchCodeSamples.php?keyword=singleton+class&category=code

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   Like         Discuss         Correct / Improve     singleton  code  coding  design pattern     Asked in 1 Companies      Intermediate        frequent

 Q290. 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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Very frequently asked to fresh graduates. Frequently asked in NSEiT and Accenture India
 Q291. Write a program to Generate prime numbers till a given numberCore Java
Ans. public class Main {
public static void main(String args[]) {
int number = 2;
int count = 0;
long sum = 0;
int givenNumber = 1000;
while (count < givenNumber) {
if (isPrimeNumber(number)) {
sum = number;
count;
}
number;
}
System.out.println(sum);
}
private static boolean isPrimeNumber(int number) {
for (int i = 2; i <= number / 2; i) {
if (number % i == 0) {
return false;
}
}
return true;
}
}

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   Like         Discuss         Correct / Improve     generate prime numbers  code  coding     Asked in 5 Companies      basic        frequent

 Q292. What will the following code print ?

Integer a = 100, b =100;
Integer c = 1000, d = 1000;
System.out.println(a == b);
System.out.println(c ==d);		Core Java
Ans. false
false

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   Like         Discuss         Correct / Improve     object equality  code  coding        frequent

  Q293. 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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   Like         Discuss         Correct / Improve     multiple inheritance  object oriented programming (oops)  oops concepts   inheritance  object oriented programming (oops)  oops concepts   oops concept     Asked in 10 Companies        frequent

  Q294. What is a Destructor ? Do we have Destructors in Java ?Core Java
Ans. Destructor is used to de-allocate memory allocated by objects.

There are no destructors in Java. Alternatively, Java provides Automatic garbage collection i.e automatically releasing the un-referenced memory.

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Frequently asked.
 Q295. What should a class do if its implementing an interface ?Core Java
Ans. It should either implement all interface methods or declare unimplemented methods as abstract.

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   Like         Discuss         Correct / Improve     interfaces     Asked in 1 Companies      Basic        frequent
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 Q296. What should a class do if its extending an abstract class ?Core Java
Ans. It should either implement the abstract methods or re-declare them abstract.

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   Like         Discuss         Correct / Improve     abstract class     Asked in 2 Companies      Basic        Frequent

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