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Interview Questions and Answers for 'Atos' - 70 question(s) found - Order By Newest

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Very frequently asked. Among first few questions in almost all interviews. Among Top 5 frequently asked questions. Frequently asked in Indian service companies (HCL,TCS,Infosys,Capgemini etc based on multiple feedback )
  Q1. Difference between == and .equals() ?Core Java
Anonymous
Ans. "equals" is the method of object class which is supposed to be overridden to check object equality, whereas "==" operator evaluate to see if the object handlers on the left and right are pointing to the same object in memory.

x.equals(y) means the references x and y are holding objects that are equal. x==y means that the references x and y have same object.

Sample code:

String x = new String("str");
String y = new String("str");

System.out.println(x == y); // prints false
System.out.println(x.equals(y)); // prints true

  Sample Code for equals

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   Like         Discuss         Correct / Improve     java   string comparison   string   object class   ==    equals   object equality  operator     Asked in 289 Companies      basic        frequent

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Frequently asked in Infosys and HCL Technologies ( Based on 2 feedback )
 Q2. What are different ways of object creation in Java ?Core Java
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Ans. Using new operator - new xyzClass()

Using factory methods - xyzFactory.getInstance( )

Using newInstance( ) method - (Class.forName(xyzClass))emp.newInstance( )

By cloning an already available object - (xyzClass)obj1.clone( )

  Sample Code for object initialization using clone

  Sample Code for object initialization using getInstance

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   Like         Discuss         Correct / Improve     java   oops   object creation   new operator   class.forname   cloning   ebay     Asked in 9 Companies      expert


Frequently asked.
 Q3. If you are given a choice to use either ArrayList and LinkedList, Which one would you use and Why ?Core Java
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Ans. ArrayList are implemented in memory as arrays and hence allows fast retrieval through indices but are costly if new elements are to be inserted in between other elements. LinkedList allows for constant-time insertions or removals using iterators, but only sequential access of elements

1. Retrieval - If Elements are to be retrieved sequentially only, Linked List is preferred.

2. Insertion - If new Elements are to be inserted in between other elements , Linked List is preferred.

3. Search - Binary Search and other optimized way of searching is not possible on Linked List.

4. Sorting - Initial sorting could be pain but lateral addition of elements in a sorted list is good with linked list.

5. Adding Elements - If sufficiently large elements needs to be added very frequently ,Linked List is preferable as elements don't need consecutive memory location.

  Sample Code for ArrayList

  Sample Code for LinkedList

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   Like         Discuss         Correct / Improve     java   collections   list   arraylist   linkedlist   difference between   architecture   data structure   ebay     Asked in 2 Companies      basic        frequent

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Frequently asked question in companies using Hibernate.
  Q4. What is Lazy Initialization in Hibernate ?Hibernate
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Ans. It's a feature to lazily initialize dependencies , relationship and associations from the Database. Any related references marked as @OneToMany or @ManyToMany are loaded lazily i.e when they are accessed and not when the parent is loaded.

  Sample Code for Lazy Initialization

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   Like         Discuss         Correct / Improve     hibernate   lazy loading hibernate   lazy initialization hibernate   architecture     Asked in 77 Companies      Basic        frequent

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  Q5. Explain OOPs

or

Explain OOPs Principles

or

Explain OOPs Concepts

or

Explain OOPs features

or

Tell me something about OOPs
Core Java2017-06-13 08:25:45

Ans. OOPs or Object Oriented Programming is a Programming model which is organized around Objects instead of processes. Instead of a process calling series of processes, this model stresses on communication between objects. Objects that all self sustained, provide security by encapsulating it's members and providing abstracted interfaces over the functions it performs. OOP's facilitate the following features

1. Inheritance for Code Reuse
2. Abstraction for modularity, maintenance and agility
3. Encapsulation for security and protection
4. Polymorphism for flexibility and interfacing

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   Like         Discuss         Correct / Improve     oops  oops features     Asked in 236 Companies      basic        frequent


Very frequently asked. Favorite question in Walk in Drive of many Indian service companies.
  Q6. What is the difference between ArrayList and LinkedList ?Core Java
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Ans. Underlying data structure for ArrayList is Array whereas LinkedList is the linked list and hence have following differences -

1. ArrayList needs continuous memory locations and hence need to be moved to a bigger space if new elements are to be added to a filled array which is not required for LinkedList.

2. Removal and Insertion at specific place in ArrayList requires moving all elements and hence leads to O(n) insertions and removal whereas its constant O(1) for LinkedList.

3. Random access using index in ArrayList is faster than LinkedList which requires traversing the complete list through references.

4. Though Linear Search takes Similar Time for both, Binary Search using LinkedList requires creating new Model called Binary Search Tree which is slower but offers constant time insertion and deletion.

5. For a set of integers you want to sort using quicksort, it's probably faster to use an array; for a set of large structures you want to sort using selection sort, a linked list will be faster.

  Sample Code for ArrayList

  Sample Code for LinkedList

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   Like         Discuss         Correct / Improve     collections   java   data structures   arraylist   linkedlist     Asked in 61 Companies      Basic        frequent

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Basic and Very Frequently asked.
  Q7. What is Polymorphism in Java ?Core Java2016-11-06 09:10:54

Ans. Polymorphism means the condition of occurring in several different forms.

Polymorphism in Java is achieved in two manners

1. Static polymorphism is the polymorphic resolution identified at compile time and is achieved through function overloading whereas

2. Dynamic polymorphism is the polymorphic resolution identified at runtime and is achieved through method overriding.

  Sample Code for overloading

  Sample Code for overriding

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   Like         Discuss         Correct / Improve     polymorphism  object oriented programming (oops)  oops concepts  oops concepts     Asked in 107 Companies      Basic        frequent

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Very Frequently asked. Have been asked in HCL Technologies very frequently ( based on 3 feedback ). Among first few questions in many interviews.
  Q8. Differences between abstract class and interface ?Core Java
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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     Asked in 65 Companies      basic        frequent


Very Frequently asked across all type of companies and across all levels.
  Q9. Difference between Public, Private, Default and Protected ?Core Java
Anonymous
Ans. Private - Not accessible outside object scope.

Public - Accessible from anywhere.

Default - Accessible from anywhere within same package.

Protected - Accessible from object and the sub class objects.

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 Q10. What is the difference between the following two code lines ?

1. new OuterClass().new InnerClass();

2. new OuterClass.InnerClass();
Core Java2016-06-30 14:45:37

Ans. In first case we are trying to initialize Inner class object using the instance of Outer Class whereas in second case we are trying to initialize the Inner class object directly using the Outer class name.

In second case , Inner class is "static inner class" as we cannot access "non static inner class" using Classname alone.

In first case, the inner class could be either "static inner class" or "non static inner class".

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   Like         Discuss         Correct / Improve     inner classes  inner class   static inner class   new operator


Usually asked in relation to casting and ClassCastException.
 Q11. What is instanceOf operator ? Explain it's use ?Core Java2017-06-12 07:58:22

Ans. The operator instanceOf is used to verify if the specified object is the instance of specified class or interface.

Syntax if(x instanceOf ABC)

where x is an object reference and ABC could be a class name or interface name. The above statement will be true if x holds an object that is an instance of ABC or any of the child class of ABC or if x holds an object that implements ABC.

instanceOf operator is used to verify in case of downcasting. For ex -

DerivedClass extends BaseClass

x is the reference of BaseClass but holds DerivedClass object ( Polymorphism )

There is an operation that is defined in Derived Class, let's say derivedClassMethod()

We cannot call derivedClassMethod() directly using x as x is reference of BaseClass and not DerivedClass and hence can only access methods that are defined in BaseClass and overridden in derived class.

Though we can cast it to DerivedClass as following
((DerivedClass)x).derivedClassMethod();

But it may throw ClassCastException in case x doesn't hold an instance of DerivedClass at that point.

So before casting it to DerivedClass we may like to make sure that it is an instance of DerivedClass and hence won't throw ClassCastException.

So we make a check for it

if(x instanceOf DerivedClass) {
((DerivedClass)x).derivedClassMethod();
}

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   Like         Discuss         Correct / Improve     instanceOf  instanceOf operator  Why we need instanceOf operator  use of instanceOf operator     Asked in 2 Companies      Intermediate        frequent


 Q12. How to find whether a given integer is odd or even without use of modulus operator in java?Core Java
Admin
info@buggybread.com
Ans. public static void main(String ar[])
{
int n=5;
if((n/2)*2==n)
{
System.out.println("Even Number ");
}
else
{
System.out.println("Odd Number ");
}
}

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   Like         Discuss         Correct / Improve     java   code   coding   tricky questions   interesting questions   modulus operator     Asked in 4 Companies        frequent


 Q13. What are the design considerations while making a choice between using interface and abstract class ?Core Java
Anonymous
Ans. Keep it as a Abstract Class if its a "Is a" Relationsship and should do subset/all of the functionality. Keep it as Interface if its a "Should Do" relationship.

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   Like         Discuss         Correct / Improve     java   oops   abstract classes   interfaces   advanced     Asked in 3 Companies


 Q14. According to Java Operator precedence, which operator is considered to be with highest precedence?Core Java
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Ans. Postfix operators i.e () [] . is at the highest precedence.

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 Q15. Difference between new operator and Class.forName().newInstance() ?
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Ans. new operator is used to statically create an instance of object. newInstance() is used to create an object dynamically ( like if the class name needs to be picked from configuration file ). If you know what class needs to be initialized , new is the optimized way of instantiating Class.

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   Like         Discuss         Correct / Improve     java   oops   object instantiation   object creation   class.forname   newinstance   new operator   difference between   advanced      intermediate


 Q16. What is comparator interface used for ?Core Java
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Ans. The purpose of comparator interface is to compare objects of the same class to identify the sorting order. Sorted Collection Classes ( TreeSet, TreeMap ) have been designed such to look for this method to identify the sorting order, that is why class need to implement Comparator interface to qualify its objects to be part of Sorted Collections.

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Frequently asked.
  Q17. What is an Iterator?Core Java
Anonymous
Ans. Iterator is an interface that provides methods to iterate over any Collection.

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   Like         Discuss         Correct / Improve     java   collections   iterator     Asked in 11 Companies      basic        frequent


Frequently asked in CTS ( Based on 2 feedback )
  Q18. What is the difference between comparable and comparator in java.util pkg?Core Java
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Ans. Comparable interface is used for single sequence sorting i.e.sorting the objects based on single data member where as comparator interface is used to sort the object based on multiple data members.

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   Like         Discuss         Correct / Improve     java   java.util   comparable   comparator   collections     Asked in 23 Companies      basic        frequent


 Q19. Difference between Class#getInstance() and new operator ?
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Ans. Class.getInstance doesn't call the constructor whereas if we create an object using new operator , we need to have a matching constructor or copiler should provide a default constructor.

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   Like         Discuss         Correct / Improve     java   constructor   object creation   default constructor   getinstance   new operator


 Q20. What is the difference between >> and >>>?
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Ans. Both bitwise right shift operator ( >> ) and bitwise zero fill right shift operator ( >>> ) are used to shift the bits towards right. The difference is that >> will protect the sign bit whereas the >>> operator will not protect the sign bit. It always fills 0 in the sign bit.

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 Q21. Which Java operator is right associative?Core Java
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Ans. The = operator is right associative.

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 Q22. What are few iterator classes provided by Java ?
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Ans. http://www.buggybread.com/2015/01/java-iterator-classes-and-interfaces.html

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   Like         Discuss         Correct / Improve     java   collections   iterator


 Q23. In which cases isn't instanceof operator a bad practice?Core Java
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Ans. To avoid ClassCastException.

Though the following code will compile fine but will result in ClassCastException during runtime.

Fruit fruit = new Apple();
Banana banana = Banana(fruit); // ClassCastException


This code will not give compile time error as Banana and Fruit are related as Banana either extends or implement Fruit, So downcasting is acceptable. With this code we assume that the Fruit handler will have the Apple object at that point, violating which the code will throw the exception.

This exception can be avoided by following code.

Fruit fruit = new Apple();
if(fruit instanceOf Banana){
Banana banana = Banana(fruit); // ClassCastException
}

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 Q24. Difference between prefix and postfix increment operator ?
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Ans. Prefix operator performs the increment and then assignment whereas its inverse for postfix operator.

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 Q25. What are fail-fast Iterators ?Core Java2016-06-09 09:27:36

Ans. Fail-fast iterators detect illegal concurrent modification during iteration and fail quickly and cleanly rather than risking arbitrary, non deterministic behavior at an undetermined time in future. Example could be of an Iterator failing if it smells ConcurrentModificationException.

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   Like         Discuss         Correct / Improve     fail-fast Iterators  Iterators     Asked in 5 Companies      intermediate


 Q26. Write code to check if an integer is odd or even using ternary operator

Ans. http://javasearch.buggybread.com/CodeSnippets/searchCodeSamples.php?&category=code&searchOption&keyword=963

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   Like         Discuss         Correct / Improve     ternary operator  code  coding


 Q27. Is Iterator a class ?

Ans. No, iterator is an interface that is used to parse through the elements of a Collection

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 Q28. What is Associativity while evaluating a Java statement ?Core Java

Ans. Associativity determines whether an expression is evaluated left-right or right-left. When an expression has two operators with the same precedence, the expression is evaluated according to its associativity.

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 Q29. Is New Keyword a method Name ?Core Java2016-06-12 20:15:01

Ans. No, Its an Operator.

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Rarely asked as it was introduced with Java 8.
 Q30. What is the use of :: operator wef from Java 8 ?Core Java2016-07-25 13:27:57

Ans. We can refer to a function using this operator like System.out.println(intList.stream().reduce(Math::max).get());

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   Like         Discuss         Correct / Improve     :: operator   lambda expression  java 8


 Q31. What is the difference between = and == in Java ?Core Java2016-09-02 08:12:45

Ans. = is the assignment operator that assigns the result of the expression on the right to the variable on the left, whereas

== is the operator to check object equality to see if the reference on left and right are pointing to the same object. For primitive types, its used to check if both variables holds the same value.

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   Like         Discuss         Correct / Improve     =  ==  assignment operator  object equality  difference between      Basic


 Q32. How is == operator different for objects and primitive types ? Core Java2016-09-02 08:14:44

Ans. For objects or references, == operator check if the reference on left and right points to the same object.

For primitive types or variables, == operator check if the variable on left and right holds the same value.

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   Like         Discuss         Correct / Improve     ==  object equality  operator      Basic


 Q33. Explain what happens when insertion is performed in case of ArrayList and LinkedList.Data Structure2017-10-26 15:52:53

Ans. Array List works on Array and when we add an element in middle of the list, Array List need to update the index of all subsequent elements. I the capacity is full, it even may need to move the whole list to a new memory location . Linked List works on Double linked list algorithm and all it has to do is to adjust the address of the previous and next elements.

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   Like         Discuss         Correct / Improve     arraylist vs linkedlist  collections  list     Asked in 2 Companies


 Q34. How Spliterator in Java 8 different than iterator ?Core Java2016-11-24 09:44:49

Ans. Though there are many differences the way internally they both iterates the collections and streams respectively, but the main difference in performance that is achieved by spliterator as it can iterate Streams in Parallel whereas iterator only iterates collections sequentially.

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   Like         Discuss         Correct / Improve     java8  java 8  spliterator  java 8 streams  streams


 Q35. Which is better in terms of performance - Iterator or Spliterator ?Core Java2016-11-24 09:46:26

Ans. Spliterator has better performance potential than iterators but only if the potential is used. Spliterator can iterate streams in parallel as well as in sequence whereas iterator can only iterate in sequence.

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   Like         Discuss         Correct / Improve     iterator  collections  streams  parallel streams  Spliterator


Frequently asked Generic Question.
  Q36. Why do you want to work for our company ?General2016-11-30 21:01:09

Ans. [Open Ended Answer]

Usually answered stating your keen interest in the role offered and challenges and opportunities the role offers.

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   Like         Discuss         Correct / Improve          Asked in 42 Companies        frequent


  Q37. Difference between Array and ArrayList ?Core Java2016-12-15 14:13:12

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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   Like         Discuss         Correct / Improve     array  arraylist     Asked in 11 Companies      basic        frequent


 Q38. Which type of memory is cleaned / recovered by garbage collection - stack or heap ?Core Java2016-12-21 13:09:29

Ans. Heap memory.

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   Like         Discuss         Correct / Improve     memory management  stack  heap  garbage collection     Asked in 2 Companies


 Q39. Which operators in Java have highest precedence ?Core Java2017-01-07 17:00:43

Ans. Braces, i.e () and [] have the highest precedence

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 Q40. Does java supports operator overloading ?Core Java2017-01-09 09:40:40

Ans. No

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   Like         Discuss         Correct / Improve     operator overloading     Asked in 1 Companies      basic


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