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Interview Questions and Answers - Order By Rating | ||||
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Ans. Enumeration Iterator List iterator | ||||
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Like Discuss Correct / Improve  cursors  iterator | ||||
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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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Like Discuss Correct / Improve  sizeOf  size of object  sizeOf operator Asked in 1 Companies   rare | ||||
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Ans. No | ||||
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Like Discuss Correct / Improve  operator overloading Asked in 1 Companies basic | ||||
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Ans. Braces, i.e () and [] have the highest precedence | ||||
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Like Discuss Correct / Improve  java operators | ||||
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Ans. Heap memory. | ||||
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Like Discuss Correct / Improve  memory management  stack  heap  garbage collection Asked in 2 Companies | ||||
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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 | ||||
Frequently asked Generic Question. | ||||
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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 | ||||
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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 | ||||
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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 | ||||
Basic and Very Frequently asked. | ||||
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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 108 Companies Basic   frequent | ||||
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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 | ||||
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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 | ||||
Rarely asked as it was introduced with Java 8. | ||||
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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 | ||||
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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 | ||||
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Ans. No, Its an Operator. | ||||
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Like Discuss Correct / Improve  new keyword  operator | ||||
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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 | ||||
Very Frequently asked across all type of companies and across all levels. | ||||
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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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Like Discuss Correct / Improve  java   oop   access specifier   public   private   default   protected   public vs private vs default vs protected Asked in 12 Companies basic   frequent | ||||
Try 1 Question(s) Test | ||||
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 ) and Epam Systems | ||||
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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   == vs equals   equals vs == Asked in 294 Companies basic   frequent | ||||
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Frequently asked. | ||||
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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 | ||||
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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 | ||||
Frequently asked in CTS ( Based on 2 feedback ) | ||||
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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 | ||||
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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 | ||||
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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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Like Discuss Correct / Improve  java   operators   bitwise operators   binary shift   right shift | ||||
Frequently asked in Infosys and HCL Technologies ( Based on 2 feedback ) | ||||
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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 | ||||
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Ans. Postfix operators i.e () [] . is at the highest precedence. | ||||
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Like Discuss Correct / Improve  java   operators   operator precedence Asked in 2 Companies | ||||
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Ans. The = operator is right associative. | ||||
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Like Discuss Correct / Improve  java   operators   = operator | ||||
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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 | ||||
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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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Like Discuss Correct / Improve  java   code   coding   tricky questions   interesting questions   modulus operator Asked in 4 Companies   frequent | ||||
Frequently asked. | ||||
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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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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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Like Discuss Correct / Improve  java   collections   treemap   treeset   comparator Asked in 2 Companies Intermediate | ||||
Try 2 Question(s) Test | ||||