Frequently asked Interview Questions and Answers

Interview Questions and Answers - Order By Newest

Very Frequently asked across all type of companies and across all levels.

Q41. Difference between Public, Private, Default and Protected ?

Core Java

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.

Help us improve. Please let us know the company, where you were asked this question :

_{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

Q42. What will this code print ?

String a = new String ("TEST");
String b = new String ("TEST");
if(a == b) {
System.out.println ("TRUE");
} else {
System.out.println ("FALSE");
}

Core Java

Ans. FALSE. == operator compares object references, a and b are references to two different objects, hence the FALSE. .equals method is used to compare string object content.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve string string class java == object references coding Asked in 2 Companies basic frequent}

Try 1 Question(s) Test

Frequently asked question for intermediate developers. Frequently asked in HCL Technologies and EPAM.

Q43. What is Volatile keyword used for ?

Core Java

Ans. Volatile is a declaration that a variable can be accessed by multiple threads and hence shouldnt be cached.

Sample Code for volatile

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java oops synchronization volatile java keywords Asked in 42 Companies intermediate frequent}

Try 1 Question(s) Test

Q44. Difference between SAX and DOM Parser ?

Xml

Ans. A DOM (Document Object Model) parser creates a tree structure in memory from an input document whereas A SAX (Simple API for XML) parser does not create any internal structure.

A SAX parser serves the client application always only with pieces of the document at any given time whereas A DOM parser always serves the client application with the entire document no matter how much is actually needed by the client.

A SAX parser, however, is much more space efficient in case of a big input document whereas DOM parser is rich in functionality.

Use a DOM Parser if you need to refer to different document areas before giving back the information. Use SAX is you just need unrelated nuclear information from different areas.

Xerces, Crimson are SAX Parsers whereas XercesDOM, SunDOM, OracleDOM are DOM parsers.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java xml parsers sax dom parser difference architecture technical lead technical architect markup language sax vs dom Asked in 14 Companies frequent}

Try 1 Question(s) Test

Very frequently asked.Usually among first few questions.

Q45. What is MVC ?

Design

Ans. MVC is a Design Pattern that facilititates loose coupling by segregating responsibilities in a Web application

1. Controller receives the requests and handles overall control of the request
2. Model holds majority of the Business logic, and
3. View comprise of the view objects and GUI component

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve j2ee mvc mvc design pattern design pattern struts spring web application web frameworks ebay Asked in 60 Companies basic frequent}

Try 1 Question(s) Test

Frequently asked to fresh graduates and less experienced.

Q46. Difference between Composition and Inheritance ?

Core Java

Ans. Inheritance means a object inheriting reusable properties of the base class. Compositions means that an abject holds other objects.

In Inheritance there is only one object in memory ( derived object ) whereas in Composition , parent object holds references of all composed objects.

From Design perspective - Inheritance is "is a" relationship among objects whereas Composition is "has a" relationship among objects.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java oops oops concepts inheritance object oriented programming (oops) oops concepts composition object oriented programming (oops) oops concepts difference between basic interview question Asked in 12 Companies basic frequent}

Try 2 Question(s) Test

Q47. How to find whether a given integer is odd or even without use of modulus operator in java?

Core Java

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 ");
}
}

Help us improve. Please let us know the company, where you were asked this question :

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

Q48. What do you look for when you do code review ?

Core Java

Ans. Modularity - First sign of good code is whether it has been segregated into methods and classes appropriately. I dont mind it in excess because I believe that is forward looking strategy as applications tends to expand and eventually become hard to read.

Self Explanatory - Variables and methods should be named in a way that the code should be self explanatory even without comments. Use of Constant variables to explain use of literal.

Proper Code Reuse - If there is anything being reused , it should be moved to parent classes / methods.

Proper composition calls - Composed hierarchy should not be access in just single line. One or two levels is ok but having multiple levels make it hard to read and debug.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve code review clean code Asked in 1 Companies intermediate frequent}

Frequently asked to fresh graduates and less experienced developers.

Q49. Explain multithreading in Java ?

Core Java

Ans. 1. Multithreading provides better interaction with the user by distribution of task

2. Threads in Java appear to run concurrently, so it provides simulation for simultaneous activities.The processor runs each thread for a short time and switches among the threads to simulate sim-ultaneous execution (context-switching) and it make appears that each thread has its own processor.By using this feature, users can make it appear as if multiple tasks are occurring simultaneously when, in fact, each is running for only a brief time before the context is switched to the next thread.

3. We can do other things while waiting for slow I/O operations.In the java.iopackage, the class InputStreamhas a method, read(), that blocks until a byte is read from the stream or until an IOExceptionis thrown. The thread that executes this method cannot do anything elsewhile awaiting the arrival of another byte on the stream.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java threads multi threading concurrency multithreading Asked in 5 Companies intermediate frequent}

Try 1 Question(s) Test

Q50. What are wrapper classes ?

Core Java

Ans. They are wrappers to primitive data types. They allow us to access primitives as objects.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java data types wrapper classes Asked in 3 Companies basic frequent}

Very frequently asked. Usually asked in different variants like Diff between StringBuffer , String Builder ; Difference between StringBuilder and String class; Choice between these classes etc.

Q51. What is the difference between StringBuffer and String class ?

Core Java

Ans. A string buffer implements a mutable sequence of characters. A string buffer is like a String, but can be modified. At any point in time it contains some particular sequence of characters, but the length and content of the sequence can be changed through certain method calls.

The String class represents character strings. All string literals in Java programs, such as "abc" are constant and implemented as instances of this class; their values cannot be changed after they are created.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java string stringbuffer frequently asked Asked in 18 Companies basic frequent}

Try 1 Question(s) Test

Q52. What is JDBC? Describe the steps needed to execute a SQL query using JDBC.

Database

Ans. The JDBC is a pure Java API used to execute SQL statements. It provides a set of classes and interfaces that can be used by developers to write database applications.

The steps needed to execute a SQL query using JDBC:

1. Open a connection to the database.
2. Execute a SQL statement.
3. Process th results.
4. Close the connection to the database.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java jdbc db connectivity Asked in 2 Companies basic frequent}

Q53. How to implement an immutable class ?

Core Java

Ans. We can make a class immutable by

1. Making all methods and variables as private.

2. Setting variables within constructor.

Public Class ImmutableClass{

private int member;
ImmutableClass(int var){
member=var;
}
}

and then we can initialize the object of the class as

ImmutableClass immutableObject = new ImmutableClass(5);

Now all members being private , you cant change the state of the object.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java oops immutable immutability immutable immutability class technical lead Asked in 5 Companies intermediate frequent}

Try 2 Question(s) Test

Frequently asked to fresh graduates.

Q54. What is a Deadlock ?

Operating System

Ans. When two threads are waiting each other and cant precede the program is said to be deadlock.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java threads multi threading operating system deadlock concurrency Asked in 23 Companies basic frequent}

Frequently asked to fresh graduates.

Q55. Explain Thread States ?

Operating System

Ans. Runnable - waiting for its turn to be picked for execution by the thread schedular based on thread priorities.

Running - The processor is actively executing the thread code. It runs until it becomes blocked, or voluntarily gives up its turn.

Waiting: A thread is in a blocked state while it waits for some external processing such as file I/O to finish.

Sleeping - Java threads are forcibly put to sleep (suspended) with Thread.sleep. they can resume using Thread.resume method.

Blocked on I/O - Will move to runnable after I/O condition like reading bytes of data etc changes.

Blocked on synchronization - Will move to Runnable when a lock is acquired.

Dead - The thread is finished working.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java threads multi threading scheduling thread states basic interview question Asked in 1 Companies basic frequent}

Try 2 Question(s) Test

Frequently asked. Among first few questions in the J2EE segment of interview.

Q56. What is deployment descriptor ?

or

What is the use of deployment descriptor ?

Java EE

Ans. Deployment Descriptor which is usually web.xml is used to specify the classes, resources and configuration of the application and how the web server uses them to serve web requests.This file is usually added to WEB-INF folder and contains following

* Servlet entries and url mapping
* Plugins
* Some info regarding authentication / filters
* Landing Page
* Event Handlers

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve web.xml servlets deployment descriptor Asked in 15 Companies basic frequent}

Try 1 Question(s) Test

Q57. Difference beween HashSet and TreeSet ?

Core Java

Ans. 1. HashSet doesnt maintain its elements in any specific order and is all random whereas TreeSet maintains elements in natural order 9 order defined by the equals method of TreeSet element type )

2. TreeSet doesnt allow null elements whereas HashMap does.

3. As TreeSet orders elements and is hence insertion is comparatively slower.

4. HashSet performs basic operations like add(), remove(), contains(), size() etc. in a constant size time. A TreeSet performs these operations at the order of log(n) time.

5. HashMap in Java internally backs a HashSet. A NavigableMap backs a TreeSet internally.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve collections hashset treeset set hashet vs treeset Asked in 4 Companies Basic frequent}

Try 1 Question(s) Test

Frequently asked in high end product companies. Frequently asked in Deloitte.

Q58. How is Hashmap internally implemented in Java ?

Core Java

Ans. https://medium.com/javarevisited/internal-working-of-hashmap-in-java-97aeac3c7beb#:~:text=HashMap%20internally%20uses%20HashTable%20implementation,the%20entries%20into%20the%20map.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve hashmap collections hashmap internal implementation Asked in 20 Companies expert frequent}

Q59. Which elements of a class are ignored during serialization ?

Core Java

Ans. 1. Objects are serialized and not classes and hence Static variables are ignored.

2. Transient is an explicit declaration to ignore the variable during serialization and hence transient instance variables are ignored too.

3. Base class instance variables if the base class hasn't been declared serializable.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve serialization Asked in 1 Companies intermediate frequent}

Try 1 Question(s) Test

Q60. What is the difference between Graph's Breadth first and Depth First algorithm ?

Algorithm

Ans. In Breadth first algorithm, all the adjacent nodes of the starting node is visited first and then the same rule is followed while moving inwards whereas

In Depth first algorithm, all the nodes of a single traversal path are visited first till a cycle or an end is found.

For example , given the following entries of adjacent nodes

1,2
1,3
1,6
2,4
2,5
3,6

The Breadth first path would be

1,2,3,6,4,5

and Depth first path would be

1,2,4,5,3,6

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve graph traversal breadth first vs depth first frequent}

Q61. What are the different types of inner classes ?

Core Java

Ans. Simple Inner Class,
Local Inner Class,
Anonymous Inner Class,
Static Nested Inner Class.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java inner classes classes Asked in 6 Companies basic frequent}

Try 1 Question(s) Test

Frequently asked in Indian Service Companies. Tech Mahindra ( Based on 3 inputs ) and Infosys ( 3 inputs )

Q62. What is the difference between List, Set and Map ?

or

What are the different Java Collections Interfaces ?

Core Java

Ans. List - Members are stored in sequence in memory and can be accessed through index.
Set - There is no relevance of sequence and index. Sets doesn't contain duplicates whereas multiset can have duplicates.
Map - Contains Key , Value pairs.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java collections list set map list vs set vs map Asked in 8 Companies basic frequent}

Try 1 Question(s) Test

Q63. Does Java support Multiple Inheritance ?

Core Java

Ans. Java doesn't support multiple inheritance. Interfaces does't facilitate inheritance and hence implementation of multiple interfaces doesn't make multiple inheritance.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java oop oop concepts inheritence multiple inheritence basic interview question Asked in 10 Companies basic frequent}

Try 1 Question(s) Test

Frequently asked at HCL Technologies ( Based on 3 feedback )

Q64. Difference between Checked and Unchecked exceptions ?

Core Java

Ans. Checked exceptions are the exceptions for which compiler throws an errors if they are not checked whereas unchecked exceptions are caught during run time only and hence can't be checked.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java exceptions checked exceptions unchecked exceptions exception handling checked vs unchecked exceptions Asked in 39 Companies basic frequent}

Try 1 Question(s) Test

Very frequently asked. Favorite question in Walk in Drive of many Indian service companies.

Q65. What is a Final Variable ?

Core Java

Ans. Final variable is a variable constant that cannot be changed after initialization.

Sample Code for final variable

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve oops java final final variable basic interview question Asked in 12 Companies basic frequent}

Try 1 Question(s) Test

Q66. Difference between Abstract and Concrete Class ?

Core Java

Ans. Abstract classes are only meant to be sub classed and not meant to be instantiated whereas concrete classes are meant to be instantiated.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java oops abstract classes Abstract vs Concrete Class Asked in 1 Companies basic frequent}

Q67. Difference between Vector and ArrayList ?

Core Java

Ans. Vectors are synchronized whereas Array lists are not.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java basic interview question vector arraylist collections synchronization vector vs arraylist Asked in 35 Companies basic frequent}

Q68. What is the use of Transient Keyword ?

Core Java

Ans. It in Java is used to indicate that a field should not be serialized.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java oops serialization transient java keywords Asked in 39 Companies intermediate frequent}

Try 2 Question(s) Test

Very Frequently asked. Usually asked along with String Class related questions.

Q69. What is an immutable class ?

Core Java

Ans. Class using which only immutable (objects that cannot be changed after initialization) objects can be created.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java oops immutable immutability immutable immutability class string class basic interview question Asked in 18 Companies Basic frequent}

Try 2 Question(s) Test

Frequently asked to fresh graduates and less experienced.

Q70. Which of the following is tightly bound ? Inheritance or Composition ?

Core Java

Ans. Inheritance.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve inheritance object oriented programming (oops) oops concepts java oops composition object oriented programming (oops) oops concepts Asked in 1 Companies basic frequent}

Search Interview Questions

Help us and Others Improve. Please let us know the questions asked in any of your previous interview.