Frequently asked Interview Questions and Answers

Interview Questions and Answers - Order By Newest

Q31. What is casting?

Ans. There are two types of casting, casting between primitive numeric types and casting between object references. Casting between numeric types is used to convert larger values, such as double values, to smaller values, such as byte values. Casting between object references is used to refer to an object by a compatible class, interface, or array type reference

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

_{Like Discuss Correct / Improve java data types casting type casting basic interview question Asked in 8 Companies basic frequent}

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

Q32. What are the methods of Object Class ?

Core Java

Ans. clone() - Creates and returns a copy of this object.

equals() - Indicates whether some other object is "equal to" this one.

finalize() - Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.

getClass() - Returns the runtime class of an object.

hashCode() - Returns a hash code value for the object.

toString() - Returns a string representation of the object.

notify(), notifyAll(), and wait() - Play a part in synchronizing the activities of independently running threads in a program.

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

_{Like Discuss Correct / Improve java oops object class Asked in 16 Companies basic frequent}

Try 1 Question(s) Test

Almost sure to be asked in every company using any Dependency Injection framework ( Spring, Guice etc )

Q33. 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.

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

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

Usually asked in relation to casting and ClassCastException.

Q34. What is instanceOf operator ? Explain it's use ?

Core Java

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();
}

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

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

Q35. 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 among first few questions.

Q36. 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

Q37. 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}

Advanced level question frequently asked in US based companies. Recently asked in EMC and Intuit.

Q38. Can you provide some implementation of a Dictionary having large number of words ?

Solution

Ans. Simplest implementation we can have is a List wherein we can place ordered words and hence can perform Binary Search.

Other implementation with better search performance is to use HashMap with key as first character of the word and value as a LinkedList.

Further level up, we can have linked Hashmaps like ,

hashmap {
a ( key ) -> hashmap (key-aa , value (hashmap(key-aaa,value)
b ( key ) -> hashmap (key-ba , value (hashmap(key-baa,value)
....................................................................................
z( key ) -> hashmap (key-za , value (hashmap(key-zaa,value)
}

upto n levels ( where n is the average size of the word in dictionary.

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

_{Like Discuss Correct / Improve java collections hashmap binary search search algorithm advanced architecture data structure Asked in 6 Companies frequent}

Try 1 Question(s) Test

Frequently asked to fresh graduates and less experienced.

Q39. Why do we write public static void main ? Can we use some other syntax too for main ?

Core Java

Ans. 1. public is the access modifier that makes the method accessible from anywhere, static is the keyword that makes it accessible even without creating any object, void means it doesn't return anything , String args[] is the array of argument that the method receives.

2. If we use main without the string args , it will compile correctly as Java will treat it as just another method. It wont be the method "main" which Java looks for when it looks to execute the class and hence will throw

Error: Main method not found in class , please define the main method as:
public static void main(String[] args)

3. Main is not a keyword but a special string that Java looks for while initiating the main thread.

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

_{Like Discuss Correct / Improve java main method Asked in 4 Companies basic frequent}

Try 1 Question(s) Test

Q40. What are the benefits of using Spring Framework ?

Spring

Ans. Spring enables developers to develop enterprise-class applications using POJOs. The benefit of using only POJOs is that you do not need an EJB container product.

Spring is organized in a modular fashion. Even though the number of packages and classes are substantial, you have to worry only about ones you need and ignore the rest.

Spring does not reinvent the wheel instead, it truly makes use of some of the existing technologies like several ORM frameworks, logging frameworks, JEE, Quartz and JDK timers, other view technologies.

Testing an application written with Spring is simple because environment-dependent code is moved into this framework. Furthermore, by using JavaBean-style POJOs, it becomes easier to use dependency injection for injecting test data.

Spring is web framework is a well-designed web MVC framework, which provides a great alternative to web frameworks such as Struts or other over engineered or less popular web frameworks.

Spring provides a convenient API to translate technology-specific exceptions (thrown by JDBC, Hibernate, or JDO, for example) into consistent, unchecked exceptions.

Lightweight IoC containers tend to be lightweight, especially when compared to EJB containers, for example. This is beneficial for developing and deploying applications on computers with limited memory and CPU resources.

Spring provides a consistent transaction management interface that can scale down to a local transaction

Sample Code for spring

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

_{Like Discuss Correct / Improve java spring framework mvc spring container architecture technical architect java architect technical lead ioc Asked in 2 Companies basic frequent}

Q41. Difference between Static and Singleton Class ?

Core Java

Ans. 1. Static class is a class which cannot be instantiated and all its members are static whereas Singleton is the class that only permit creation of single object and then the object is reused.

2. As there is no object in Static class, it cannot participate in runtime Polymorphism.

3. As Static class doesnt allow creating objects and hence it cannot be serialized.

4. Static class body is initialized eagerly at application load time whereas Singleton object can be initiated eagerly using static blocks or lazily on first need.

5. Its not recommended to use pure static class as it fails to use many OOPs concepts.

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

_{Like Discuss Correct / Improve Static Class Singleton Static Class vs Singleton Asked in 3 Companies Intermediate frequent}

Very frequently asked in companies using SOA.

Q42. What are RESTful Web Services ?

Rest

Ans. REST or Representational State Transfer is a flexible architecture style for creating web services that recommends the following guidelines -

1. http for client server communication,
2. XML / JSON as formatiing language ,
3. Simple URI as address for the services and,
4. stateless communication.

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

_{Like Discuss Correct / Improve java web services rest java j2ee architecture Asked in 14 Companies intermediate frequent}

Frequently asked to experienced developers. Recently asked in many US interviews.

Q43. What is database deadlock ? How can we avoid them?

Database

Ans. When multiple external resources are trying to access the DB locks and runs into cyclic wait, it may makes the DB unresponsive.

Deadlock can be avoided using variety of measures, Few listed below -

Can make a queue wherein we can verify and order the request to DB.

Less use of cursors as they lock the tables for long time.

Keeping the transaction smaller.

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

_{Like Discuss Correct / Improve java database architecture Asked in 7 Companies expert frequent}

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

Q44. 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

Frequently asked Generic Question.

Q45. Why do you want to work for our company ?

General

Ans. [Open Ended Answer]

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

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

_{Like Discuss Correct / Improve Asked in 42 Companies frequent}

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

Q46. 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

Q47. 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

Q48. 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.

Q49. 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

Q50. 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

Frequently asked to fresh graduates and less experienced.

Q51. 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

Q52. Can we overload main method in Java ?

Core Java

Ans. Yes, but the overloaded main methods without single String[] argument doesn't get any special status by the JVM. They are just another methods that needs to be called explicitly.

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

_{Like Discuss Correct / Improve java main method overloading yes-no Asked in 6 Companies intermediate frequent}

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

Q53. 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}

Q54. 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.

Q55. 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

Q56. 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.

Q57. 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

Q58. 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}

Q59. 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.

Q60. 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}

Search Interview Questions

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