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Interview Questions and Answers for 'Atos' - 51 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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Frequently asked in Infosys and HCL Technologies ( Based on 2 feedback )
 Q2. What are different ways of object creation in Java ?Core Java
Admin
info@buggybread.com
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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Frequently asked question in companies using Hibernate.
  Q3. What is Lazy Initialization in Hibernate ?Hibernate
Admin
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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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Very Frequently asked. Have been asked in HCL Technologies very frequently ( based on 3 feedback ). Among first few questions in many interviews.
  Q4. 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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 Q5. 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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Usually asked in relation to casting and ClassCastException.
 Q6. 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     Trimax IT Infrastructure & Services   ultramain      Intermediate        frequent


Very Frequently asked across all type of companies and across all levels.
  Q7. 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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 Q8. According to Java Operator precedence, which operator is considered to be with highest precedence?Core Java
Admin
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Ans. Postfix operators i.e () [] . is at the highest precedence.

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 Q9. Difference between new operator and Class.forName().newInstance() ?
Admin
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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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 Q10. How to find whether a given integer is odd or even without use of modulus operator in java?Core Java
Admin
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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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 Q11. What is comparator interface used for ?Core Java
Admin
info@buggybread.com
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.
  Q12. What is an Iterator?Core Java
Anonymous
Ans. Iterator is an interface that provides methods to iterate over any Collection.

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Frequently asked in CTS ( Based on 2 feedback )
  Q13. What is the difference between comparable and comparator in java.util pkg?Core Java
Admin
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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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 Q14. 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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 Q15. 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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 Q16. Which Java operator is right associative?Core Java
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Ans. The = operator is right associative.

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 Q17. 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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 Q18. In which cases isn't instanceof operator a bad practice?Core Java
Admin
info@buggybread.com
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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 Q19. 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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 Q20. 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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 Q21. 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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 Q22. 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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 Q23. 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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 Q24. 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.
 Q25. 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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 Q26. 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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 Q27. 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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 Q28. 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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 Q29. 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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Frequently asked Generic Question.
  Q30. 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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 Q31. 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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 Q32. Does java supports operator overloading ?Core Java2017-01-09 09:40:40

Ans. No

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 Q33. Is there a way to know size of an object in Java ?Core Java2017-01-12 11:14:59

Ans. No, Java doesn't have a sizeOf operator. In C / C++ , its required to determine how much memory allocation is required which is not the case with Java. Java handles memory allocation and deallocation intrinsically.

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 Q34. What are the cursors available in Java ?Core Java2017-01-15 14:55:22

Ans. Enumeration
Iterator
List iterator

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 Q35. Explain dot(.) operator ?Core Java2017-01-19 13:53:35

Ans. Its used to access the object properties using the object reference or class properties using the Class Name. Moreover its used to access the classes and Interfaces of a package.

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 Q36. What are the different operators in Java ?Core Java2017-01-28 15:15:36

Ans. && - AND
|| - OR
! - LOGICAL NOT

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 Q37. What is the difference between && and & in Java ?Core Java2017-02-03 08:30:47

 This question is still unanswered. Can you please provide an answer.


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 Q38. What is the precedence of operators in Java ?Core Java2017-03-01 09:42:52

Ans. http://introcs.cs.princeton.edu/java/11precedence/

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 Q39. What is a mutator in Java?Core Java2017-03-10 09:45:05

Ans. Mutator is another name for setter methods, i.e the method allows for mutating the property of an object and eventually the state of the object.

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 Q40. What is the difference between Enumeration and Iterator ?Core Java2017-05-07 15:22:08

Ans. Enumeration can iterate only legacy collections like Vector , HashTable and Stack whereas Iterator can iterate both legacy and non legacy collections.

Enumeration is less safer than Iterator

Enumeration is fail safe whereas Iterator is fail fast

Iterator allows for removal of element while traversal whereas Enumeration doesn't have remove method.

Enumerations were introduced in Java 1 whereas Iterators were introduced with Java 2

Enumerations have methods like hasMoreElements and nextElement whereas Iterators have methods like hasNext, next and remove

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