Interview Questions and Answers for 'AT' | Search Interview Question

Interview Questions and Answers - Order By Newest

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

Q41. 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.

Q42. 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}

Q43. What are concepts introduced with Java 5 ?

Core Java

Ans. Generics , Enums , Autoboxing , Annotations and Static Import.

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

_{Like Discuss Correct / Improve java java5 generics enum autoboxing annotations static import rare}

Try 1 Question(s) Test

Q44. Describe what happens when an object is created in Java ?

Core Java

Ans. 1. Memory is allocated from heap to hold all instance variables and implementation-specific data of the object and its superclasses. Implemenation-specific data includes pointers to class and method data.
2. The instance variables of the objects are initialized to their default values.
3. The constructor for the most derived class is invoked. The first thing a constructor does is call the constructor for its superclasses. This process continues until the constructor for java.lang.Object is called,as java.lang.Object is the base class for all objects in java.
4. Before the body of the constructor is executed, all instance variable initializers and initialization blocks are executed. Then the body of the constructor is executed. Thus, the constructor for the base class completes first and constructor for the most derived class completes last.

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

_{Like Discuss Correct / Improve java memory management object creation advanced ebay}

Q45. 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.

Q46. 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

Q47. What is session tracking and how do you track a user session in servlets?

Java EE

Ans. Session tracking is a mechanism that servlets use to maintain state about a series requests from the same user across some period of time. The methods used for session tracking are:

User Authentication - occurs when a web server restricts access to some of its resources to only those clients that log in using a recognized username and password

Hidden form fields - fields are added to an HTML form that are not displayed in the client's browser. When the form containing the fields is submitted, the fields are sent back to the server

URL rewriting - every URL that the user clicks on is dynamically modified or rewritten to include extra information. The extra information can be in the form of extra path information, added parameters or some custom, server-specific URL change.

Cookies - a bit of information that is sent by a web server to a browser and which can later be read back from that browser.

HttpSession- places a limit on the number of sessions that can exist in memory.

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

_{Like Discuss Correct / Improve j2ee servlets session session management web applications cookies httpsession url rewriting architecture Asked in 1 Companies}

Advanced level question usually asked to senior developers , leads and architects.

Q48. How does volatile affect code optimization by compiler?

Core Java

Ans. Volatile is an instruction that the variables can be accessed by multiple threads and hence shouldn't be cached. As volatile variables are never cached and hence their retrieval cannot be optimized.

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

_{Like Discuss Correct / Improve java java keywords volatile synchronization compiler optimization variable caching architecture Asked in 3 Companies expert}

Q49. 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.

Q50. 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.

Q51. 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

Frequently asked to fresh graduates.

Q52. What is ACID ?

Database

Ans. ACID stands for Atomicity, Consistency, Isolation, Durability is a set of properties of database transactions.

Atomicity means all or nothing. i.e parts of a transaction shouldn't commit if any one of them fails. Either the whole transaction should succeed or it should be complete rollback.

Consistency means that any transaction should lead database from one stabe state to another.

Isolation means that the execution of transaction results in a system state that would be obtained if transactions were executed serially.

Durability means that when a transaction is committed it forms the permanent state of database.

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

_{Like Discuss Correct / Improve database acid Asked in 7 Companies Intermediate}

Try 1 Question(s) Test

Q53. Can constructors be synchronized in Java ?

Core Java

Ans. No. Java doesn't allow multi thread access to object constructors so synchronization is not even needed.

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

_{Like Discuss Correct / Improve synchronization synchronize constructor java multithreading yes-no advanced Asked in 1 Companies expert rare}

Q54. what is the use of cookie and session ? and What is the difference between them ?

Java EE

Ans. Cookie and Session are used to store the user information. Cookie stores user information on client side and Session does it on server side. Primarily, Cookies and Session are used for authentication, user preferences, and carrying information across multiple requests. Session is meant for the same purpose as the cookie does. Session does it on server side and Cookie does it on client side. One more thing that quite differentiates between Cookie and Session. Cookie is used only for storing the textual information. Session can be used to store both textual information and objects.

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

_{Like Discuss Correct / Improve session session management java cookies authentication web application ebay intermediate}

Q55. 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.

Q56. 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.

Q57. 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.

Q58. 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.

Q59. 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}

Q60. Can we declare static variables as transient ?

Core Java

Ans. It's weird that compiler doesn't complain if we declare transient with static variable because it makes no sense. At least a warning message saying "transient is useless in this situation" would have helped with code cleaning.

Static variables are never serialized and transient is an indication that the specified variable shouldn't be serialized so its kind of double enforcement not to serialize.

It could be that as it makes no different to the variable behavior and hence using both keywords with a variable are permitted.

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

_{Like Discuss Correct / Improve static transient serialization Asked in 1 Companies expert rare}

Try 1 Question(s) Test

Q61. Which of the following are valid declarations

1. void method(int... x){};
2. void method(int.. x){};
3. void method(int.. .x){};
4. void method(int ...x){};
5. void method(int... x){};
6. void method(int ... x){};
7. void method(int x, int... y){};
8. void method(int... x, int y){};
9. void method(int... x,int... y){};

Core Java

Ans. 1st is a valid and standard declaration.

2nd results in compilation error as only 2 dots are there.

3rd results in compilation error as three dots are not consecutive and broken.

4 through 6 may not be standard and ideal way of declarations but they are valid and will compile and work fine.

7 is valid declaration.

8 and 9 will result in compilation error as var args can only be provided to last argument.

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

_{Like Discuss Correct / Improve var args methods functions method declaration scjp ocjp}

Q62. How is string object immutable if we can concat a string to it ?

Core Java

Ans. Because it doesn't make the change in the existing string but would create a new string by concatenating the new string to previous string. So Original string won't get changed but a new string will be created. That is why when we say

str1.concat("Hello");

It means nothing because we haven't specified the reference to the new string and we have no way to access the new concatenated string. Accessing str1 with the above code will still give the original string.

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

_{Like Discuss Correct / Improve string string immutable immutability string concat}

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

Q63. 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

Q64. Does Constructor creates the object ?

Core Java

Ans. New operator in Java creates objects. Constructor is the later step in object creation. Constructor's job is to initialize the members after the object has reserved memory for itself.

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

_{Like Discuss Correct / Improve java constructor object creation intermediate rare}

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

Q65. 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

Q66. 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

Q67. Difference between the jsp scriptlet tag and jsp declaration tag?

Java EE

Ans. The jsp scriptlet tag can only declare variables not methods whereas jsp declaration tag can declare variables as well as methods.

The declaration of scriptlet tag is placed inside the _jspService() method whereas The declaration of jsp declaration tag is placed outside the _jspService() method.

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

_{Like Discuss Correct / Improve j2ee jsp scriptlet tag declaraation tag web application}

Frequently asked to fresh graduates and less experienced.

Q68. 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

Q69. 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}

Q70. Which annotations are used in Hibernate ?

Hibernate

Ans. @Entity
@Table
@Id
@Column
@Temporal
@Basic
@Enumerated
@Access
@Embeddable
@Lob
@AttributeOverride
@Embedded
@GeneratedValue
@ElementCollection
@JoinTable
@JoinColumn
@CollectionId
@GenericGenerator
@OneToOne
@OneToMany
@ManyToOne
@ManyToMany
@NotFound

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

_{Like Discuss Correct / Improve hibernate annotations}

Search Interview Questions

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