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

Interview Questions and Answers - Order By Newest

Q71. What are the Wrapper classes available for primitive types ?

Ans. boolean - java.lang.Boolean
byte - java.lang.Byte
char - java.lang.Character
double - java.lang.Double
float - java.lang.Float
int - java.lang.Integer
long - java.lang.Long
short - java.lang.Short
void - java.lang.Void

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

_{Like Discuss Correct / Improve java java5 data types wrapper classes adapter design pattern rare}

Frequently asked to fresh graduates and less experienced developers.

Q72. 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

Q73. 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}

Q74. 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}

Q75. 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}

Q76. 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

Q77. Can we access instance variables within static methods ?

Core Java

Ans. Yes.we cannot access them directly but we can access them using object reference.Static methods belong to a class and not objects whereas non static members are tied to an instance. Accessing instance variables without the instance handler would mean an ambiguity regarding which instance the method is referring to and hence its prohibited.

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

_{Like Discuss Correct / Improve java oops static static methods java keywords Asked in 1 Companies}

Frequently asked to fresh graduates.

Q78. 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.

Q79. 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

Q80. What is a ConcurrentHashMap ?

Core Java

Ans. ConcurrentHashMap is a hashMap that allows concurrent modifications from multiple threads as there can be multiple locks on the same hashmap.

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

_{Like Discuss Correct / Improve java collections hashmap map concurrenthashmap concurrenthashmap concurrency general electric ge Asked in 32 Companies rare}

Q81. What are the contents of Hibernate configuration file ( hibernate.cfg.xml ) ?

Hibernate

Ans. HBM Files ( Mapping )
DB Connection ( DB Connection String , User Name , Password , Pool Size )
SQL Dialect ( SQL variant to be generated )
Show SQL ( Show / No show SQL on Console )
Auto Commit ( True / False )

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

_{Like Discuss Correct / Improve hibernate configuration barclays Asked in 11 Companies}

Q82. Difference between Predicate, Supplier and Consumer ?

Core Java

Ans. Predicate represents an anonymous function that accepts one argument and produces a result.

Supplier represents an anonymous function that accepts no argument and produces a result.

Consumer represents an anonymous function that accepts an argument and produces no result.

Sample Code for Predicate

Sample Code for Supplier

Sample Code for Consumer

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

_{Like Discuss Correct / Improve java java8 predicate consumer supplier lambda expression predicate vs consumer vs supplier expert}

Q83. What things you would care about to improve the performance of Application if its identified that its DB communication that needs to be improved ?

Solution

Ans. 1. Query Optimization ( Query Rewriting , Prepared Statements )

2. Restructuring Indexes.

3. DB Caching Tuning ( if using ORM )

4. Identifying the problems ( if any ) with the ORM Strategy ( If using ORM )

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

_{Like Discuss Correct / Improve java db database hibernate orm at&t overstock.com performance improvement architecture technical lead architect intermediate}

Q84. Which of the following Java feature promotes access protection or Hiding ?

a. Inheritance
b. Encapsulation
c. Abstraction
d. Composition

Core Java

Ans. Encapsulation

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

_{Like Discuss Correct / Improve java java concepts java features oops concepts oops features access protection information hiding}

Q85. Why Java is not considered pure OOP's language ?

Core Java

Ans. There are 2 reasons for it.

1. Usage of Primitive types - Though Java provides classes for the primitive data types but as the usage of primitives is permissible, its considered unpure OOP's language.

2. Usage of Static members - Static members belong to the class and not objects and hence not considered fit for pure OOP's programming.

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

_{Like Discuss Correct / Improve oops object oriented programming object oriented language primitive data types Asked in 2 Companies}

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

Q86. 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

Q87. Why HashTable has been deprecated ?

Core Java

Ans. HashTable has been deprecated. As an alternative, ConcurrentHashMap has been provided. It uses multiple buckets to store data and hence much better performance than HashTable. Moreover, there is already a raw type HashMap. The only difference between the HashTable and HashMap is that Hashtable is synchronized whereas HashMap is not. Most of the synchronized collections have been deprecated and their raw alternative have been presented as preferred.Synchronization has a cost. Using synchronized collection in places where there is no need of it leads to useless utilization of resources. As these collections are rarely used in a static context or shared among threads, Java might have thought it better to just provide the raw collection and let developers implement synchronization if he feels the need to do so. HashMap is now presented as the default and the preferred way of using Map with read optimized hashing, and ConcurrentHashMap has been provided for synchronized access which provides better performance than HashTable. Because of this, Java thought it right to deprecate the use of HashTable.'

Synchronization has a cost. Using synchronized collection at a place where there is hardly any need of it would means useless utilization of resources. As these collections are rarely used in static context or shared among threads, Java might have thought it better to just provide the raw collection and let developer implement synchronization if he feels the need to do so.

As HashMap has been presented as default and preferred way of using Map with read optimized hashing, and ConcurrentHashMap has been provided for synchronized access which provides better performance than HashTable, Java thought it right to deprecate the use of HashTable.

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

_{Like Discuss Correct / Improve hashtable synchronized collections Why synchronized collections have been deprecated Why HashTable has been deprecated HashTable vs HashMap expert}

Try 3 Question(s) Test

Q88. 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

Q89. 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

Q90. What is the difference between these two method declarations ?

private static void method(String[] arg)

and

private static void method(String... arg)

Core Java

Ans. First expects the argument as a string array whereas second expects variable number of string arguments or a string array.

So we can call both by providing string array as an argument but second can be called with 0 to n string arguments which cannot be done for first.

for example - We can call second method with any of following

method();
method("Hello");
method("Hello","World");
method(new String[4]);

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

_{Like Discuss Correct / Improve var args methods method declarations functions}

Q91. If arrays cannot be resized , Why is this code valid

String[] strArray = new String[2];
strArray = new String[5];

Core Java

Ans. We are not resizing the first array here but assigning the reference strArray to a new Array with size 5.

So after line 2, We have 2 arrays in memory, one with size 2 and other with size 5 with strArray referring to second array with size 5.

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

_{Like Discuss Correct / Improve arrays array initialization}

Q92. Difference between Region , Availability zone and Edge Locations ?

Amazon Web Services (AWS)

Ans. A Region is a Geographical entity like US-East , US-West etc. Each Region may have multiple availability zones where each zone comprise of 1 or more Data Center located with each other.

Edge Locations are the sites that hosts cached content for faster delivery and for saving network traffic as they feed content from sites that are local or near to consumption.

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

_{Like Discuss Correct / Improve aws region aws availability zone aws edge location region vs availabillity zone}

Q93. 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 at HCL Technologies ( Based on 3 feedback )

Q94. 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.

Q95. 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

Q96. When are static variables loaded in memory ?

Core Java

Ans. They are loaded at runtime when the respective Class is loaded.

Sample Code for static variable

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

_{Like Discuss Correct / Improve java oops static static variable memory intermediate}

Q97. Can we serialize static variables ?

Core Java

Ans. No. Only Object and its members are serialized. Static variables are shared variables and doesn't correspond to a specific object.

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

_{Like Discuss Correct / Improve serialization java oops static static variables Asked in 1 Companies intermediate rare}

Try 2 Question(s) Test

Usually asked only to fresh graduates.

Q98. What is the difference between time slicing and preemptive scheduling ?

Operating System

Ans. In preemptive scheduling, highest priority task continues execution till it enters a not running state or a higher priority task comes into existence. In time slicing, the task continues its execution for a predefined period of time and reenters the pool of ready tasks.

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

_{Like Discuss Correct / Improve operating system scheduling threads multi threading rare}

Q99. What one should take care of, while serializing the object?

Ans. One should make sure that all the included objects are also serializable. If any of the objects is not serializable then it throws a NotSerializable Exception.

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

_{Like Discuss Correct / Improve serialization java oops object expert}

Q100. 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}

Search Interview Questions

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