Core java - Interview Questions and Answers for 'Abs' | Search Java Interview Question

Core java - Interview Questions and Answers for 'Abs' - 174 question(s) found - Order By Newest

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 )

Q1. Difference between == and .equals() ?

Core Java

^Anonymous

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

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

_{Like Discuss Correct / Improve java string comparison string object class == equals object equality operator Ebay Cerner GuideWire Expeditors Associate Revature SAIC ValueLabs Realty Redefined Bank Of America Capgemini HCL Technologies Goldman Sachs Symmetric Corp Backstop Solutions Frontier IQOR Science Vanguard eClinicalWorks Experticity Blue Cross and Blue Shield of Kansas ComTrade Banja Luka Overstock.com Intrasoft International IBM Apex Systems infoview technologies Ebix Cumulus Systems Nakisa United HealthGroup (UHG) Sopra Steria TrueCaller Mphasis Amdocs T & A Hr Solutions End2End Catalyst Code Garage Tech IQuest Management Consultants Indianmesh pvt ltd Netsmartz Meander Software UrbanPro.com Netrovert Software T & A Hr Solutions Zscaler Maven Wave Partners Basware India Emerson GCE solutions SmartData Enterprise Shivark Virtual Academy FinXera Sampoorna Consultants Samridhi KKA Technologies bebo technologies Closeloop Technologies DamcoSoft Swar Yantra Technologies SK VedaInfo Universal Trantor Software IT HAT Consulting Kindlebit Solutions Mann McGlynn AmrtData Enterprises Riconz Technologies Embryo Software Solution Corporate Stalwarts Varite Mirror Consultancy Service Wing Global IT Service Regence Adpearance IGNW Centizen Flexton Syntel Kaiser Permanente SkiData New Relic McKesson Finastra Pivotal UST Global Morgan Stanley Kroger Genesys Guardian Life SynergisticIT Leidos Expeditors Associate Polycom Compass Point ClickCare Expedia Equal Experts Dimentrix Intellect Design Arena Epam Systems Qualys Instacart ThoughtWorks Maxgen Technologies Aayansh Germinate Principal Financial Group NineScript Technologies Nihilent infrasoft technologies e-Zest Solutions Krawler Inc FundTech BNT SOFT SAPsphinx Infotech KinderTouch Accede Software Solutions LeadLake Emerson Xoriant Citrix Anonymous Content GS Lab Thermax Saama Technologies Fresherworld.com Nityo Infotech Sanofi Innoplexus Sears IT & Management Services National Stock Exchange of India Accelya Kale Tudip Technologies ITSource Technologies Sela Technology Solutions Eternus Solutions Raja Software Labs Leo TechnoSoft Shubham Housing Development Finance Serene Corporation Leo Technosoft Questionpro Sparken IT Solutions Capsilon JetSynthesys MangoSpring Subway Arezzo Sky Lenco Diagnostic Laboratories Finlogic Technologies Maxxton Cerillion Applus+ XOYAL Acloudzyn Technologies ITYX Tej IT Solutions Transworld Compressor Technologies Deskera Ebaotech Kahuna Systems Kimaya Infotech SSP Technology Boston Byte Bonellisoft Rack Infotech Intellection Software and Technologies OMVSAB IT Solutions ProductDossier Soft Infology Systems Plus Transformations StackMint HeadInfotech India EffortSys KasNet Technologies Java City iSynergy TechSys Unisoft Technologies Servient ThinkQuotient Software Medline Industries Ascent Cyber Solutions Proto-T Solutions Tinker Technologies Censhare Proto-T Solutions Henx International Technologies AlightHub Consulting Services Perpetual Infotech BestoSys Infiniti Infosystems Torqus Spectrum Tech System OreInfo Sanvi Softech Neptune Solutions XTime Web Hub Technology Coin Technologies Paramount Pictures Rocklike DMS Implant Technosoft Solutions Nabla Infotech Predikly Godwit Technologies Kanaka Consulting Aarnum Technologies Ganesh Kapure Abhinav Digicompsoft Services Shoffex.com Online Training Solutions A Plus Tree OMM Software Innovation Tanish Infotech Solution Zinist Software Mobile Sutra Playpixel Infosystem SunGuard Nihilent Siemens PLM Software Maxgen Technologies Nitor Infotech Mediaocean Yagna iQ Sigma Systems Ethon The Permanente Medical Group Reliance Industries MindCraft Software ABM Knowledgeware Trutech Web Solutions Nikhil R Gupta & Associates eMeasurematics NovelERP Solutions Web Element Solutions HDFC Bank Qualcomm Intellect Design Arena Diebold Nixdorf Sharekhan Pepperfry IRIS Business Services Wind World ZEDO Loylty Rewardz Mngt C2L Biz Chenoa Information Services Insolutions Global Vakrangee Softwares Celusion Technologies Currencies Direct Zenith System Solutions Base Information Management Exponentia DataLabs Realty Redefined Constaccent Neoquant Solutions Aureus Analytics Planfirma Technologies Pawaa Software iBhejo Fairfax County Virginia American Conservation Experience Hari Krishna Exports Core Education & Technologies Nishat Mills Industrial Market Place Krisnela Technologies Swissclear Global Samyak Software Professional Access Nexstep Infotech Concerto Software Viral Technologies Silverwing Technologies Gcom Software Inc Accel Frontline Atom Technologies Blue Star Infotech Cynapse Datamatics Global Services Flytxt Mobile Solutions Persistent Systems Onmobile Global Trianz Sasken WNS Global Services Tavant technology Edz Infomatics basic frequent}

Try 6 Question(s) Test

Advanced level question. Frequently asked in High end product companies. Frequently asked in Cognizant and Deloitte ( Based on 2 feedback )

Q2. Why is String immutable in Java ?

Core Java

^Anonymous

Ans. 1. String Pool - When a string is created and if it exists in the pool, the reference of the existing string will be returned instead of creating a new object. If string is not immutable, changing the string with one reference will lead to the wrong value for the other references.

Example -

String str1 = "String1";
String str2 = "String1"; // It doesn't create a new String and rather reuses the string literal from pool

// Now both str1 and str2 pointing to same string object in pool, changing str1 will change it for str2 too

2. To Cache its Hashcode - If string is not immutable, One can change its hashcode and hence it's not fit to be cached.

3. Security - String is widely used as parameter for many java classes, e.g. network connection, opening files, etc. Making it mutable might possess threats due to interception by the other code segment.

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

_{Like Discuss Correct / Improve java oops string string class immutable immutability advanced Barclays Jungo Cloudera Allston Man Group Prokarma Optimus Gamesys ABS TransPerfect Fidelity Deloitte Zalando Cognizant (CTS) Zeta Interactive SuccessFactors
EchoStar InterGlobe Technologies HCL Technologies Intuit JP Morgan Optimus Information Faichi Solutions Blip Adobe Subex Limited Remo Software Allstate IBM Bizmatics Bytecode Cyber Security Calsoft Systems IDS Infotech Nakisa HSBC expert frequent}

Try 4 Question(s) Test

Very frequently asked in different variations. Frequently asked in Deloitte ( 2 feedback ) , HCL Tech ( 3 feedback ) and Coginizant (CTS)

Q3. Explain the scenerios to choose between String , StringBuilder and StringBuffer ?

or

What is the difference between String , StringBuilder and StringBuffer ?

Core Java

^Anonymous

Ans. If the Object value will not change, use String Class because a String object is immutable.

If the Object value can change and will only be modified from a single thread, use StringBuilder because StringBuilder is unsynchronized(means faster).

If the Object value may change, and can be modified by multiple threads, use a StringBuffer because StringBuffer is thread safe(synchronized).

Sample Code for String

Sample Code for StringBuffer

Sample Code for StringBuilder

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

_{Like Discuss Correct / Improve java string class string stringbuilder stringbuffer Cognizant (CTS) San Jose State University (SJSU) HCL Technologies Deloitte Sophos Hitachi JPMorgan Chase IBM Kony Labs Keystone ebay TIAA Financial Services Ancestry Rakuten Accenture Accenture India QualiTest Group CDK Global InfoGain Mindfire Solutions Shopify Tk20 AppKnox RedMane Technology Fidelity travelex basic frequent}

Try 3 Question(s) Test

Q4. What do you mean by "Java is a statically typed language" ?

Core Java

^{Admin
info@buggybread.com}

Ans. It means that the type of variables are checked at compile time in Java.The main advantage here is that all kinds of checking can be done by the compiler and hence will reduce bugs.

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

_{Like Discuss Correct / Improve java statically typed language variable declaration Vanguard Viasat Natrix Technology HCL Technologies Accenture Accenture India Infosys basic frequent}

Q5. Why Char array is preferred over String for storing password?

Core Java

^{Admin
info@buggybread.com}

Ans. String is immutable in java and stored in String pool. Once it's created it stays in the pool until unless garbage collected, so even though we are done with password it's available in memory for longer duration and there is no way to avoid it. It's a security risk because anyone having access to memory dump can find the password as clear text.

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

_{Like Discuss Correct / Improve java string class string immutable immutability string pool garbage collection advanced General Motors Amura Marketing Technologies Bloomberg Innovive Expert}

Very frequently asked to Fresh graduates.

Q6. What is the difference between Encapsulation and Abstraction?

Core Java

^Anonymous

Ans. 1.Abstraction solves the problem at design level while encapsulation solves the problem at implementation level

2.Abstraction is used for hiding the unwanted data and giving relevant data. while Encapsulation means hiding the code and data into a single unit to protect the data from outside world.

3. Abstraction lets you focus on what the object does instead of how it does it while Encapsulation means hiding the internal details or mechanics of how an object does something.

4.For example: Outer Look of a Television, like it has a display screen and channel buttons to change channel it explains Abstraction but Inner Implementation detail of a Television how CRT and Display Screen are connect with each other using different circuits , it explains Encapsulation.

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

_{Like Discuss Correct / Improve java oops oops concepts encapsulation object oriented programming (oops) oops concepts abstraction basic interview question Synechron Amazon HCL Technologies Tata Consultancy (TCS) Wipro Infosys Technologies 3DPLM Software Solutions Ojas Innovative Technologies John Deere Mastek basic frequent}

Try 2 Question(s) Test

Frequently asked in Infosys and HCL Technologies ( Based on 2 feedback )

Q7. What are different ways of object creation in Java ?

Core Java

^{Admin
info@buggybread.com}

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

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

_{Like Discuss Correct / Improve java oops object creation new operator class.forname cloning ebay Intelligrape Infosys Polaris British Telecom (BT) Vyom Labs Deutsche Bank HCL Technologies Genpact Thomson Reuters expert}

Q8. What is a Lambda Expression ? What's its use ?

Core Java

^{Admin
info@buggybread.com}

Ans. Its an anonymous method without any declaration.

Lambda Expression are useful to write shorthand Code and hence saves the effort of writing lengthy Code.

It promotes Developer productivity, Better Readable and Reliable code.

Sample Code for lambda

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

_{Like Discuss Correct / Improve java java8 lambda expression architecture Axxess CACI ZonOff Dell India Wellington Management N26 Lithium Technologies DST Systems Overstock Sofi JP Morgan HCL Technologies Infosys Wipro Accenture Accenture India Eurofins Yodlee AvenData GmbH Sapient Global Markets Walmart Ebay Goldman Sachs Foundation Software HSBC Holdings Wells Fargo Marlabs ZooPlus Elastic Path CardConnect WealthFront WorldAware SpredFast Mobileum eGym EnelX Kroger GFT Technoligies Tyro Payments Mindtree KocharTech Bharti Airtel Tech Mahindra Patni Computers L&T Infotech Mphasis Mindtree Hexaware Collabera 3i Infotech IGate Kpit Technologies NIIT Technologies Trianz Persistent Systems IT Asset 1-800 contacts expert frequent}

Try 1 Question(s) Test

Very frequently asked. Favorite question in Walk in Drive of many Indian service companies. Frequently asked in HCL Technologies, TCS and Accenture.

Q9. What is the difference between final, finally and finalize() ?

Core Java

^{Admin
info@buggybread.com}

Ans. final - constant variable, objects cannot be de-referenced, restricting method overriding, restricting class sub classing.

finally - handles exception. The finally block is optional and provides a mechanism to clean up regardless of what happens within the try block. Use the finally block to close files or to release other system resources like database connections, statements etc.

finalize() - method helps in garbage collection. A method that is invoked before an object is discarded by the garbage collector, allowing it to clean up its state.

Sample Code for final

Sample Code for finally

Sample Code for finalize

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

_{Like Discuss Correct / Improve java oops final finally finalize Thomson Reuters WITS Antra Jive MorningStar VanGuard Alcatel Lucent Morningstar A9.com EPAM Nuance SirsiDynix NCR VanGuard Proofpoint Interview Disney Orbitz Worldwide GFI Informatique Canon WITS Simba Technologies Marlabs American Well Global Relay L&T Infotech HCL Technologies Tata Consultancy (TCS) Wipro Infosys Accenture Accenture India Jive Salesforce Deegit NTT DATA Proofpoint Morningstar Bank Of America Manhattan Associates Optum NorthPoint Nok Nok Labs Simba Technologies
Rhino Africa Solutionreach V Soft Consulting EBay Cognizant (CTS) IBM ExactTargetKewill CV Holdings Symphony Cubic Web solutions Star International FatWire Mindteck Dark Horse TrueCaller marlabs Proofpoint basic frequent}

Try 4 Question(s) Test

Do you think these are the Best Java Frameworks ?

OpenXava

SPRING MVC

Apache Stripes

Check everything
that is Best in Java

Click Here

Q10. Explain OOPs

or

Explain OOPs Principles

or

Explain OOPs Concepts

or

Explain OOPs features

or

Tell me something about OOPs

Core Java

^{2017-06-13 08:25:45}

Ans. OOPs or Object Oriented Programming is a Programming model which is organized around Objects instead of processes. Instead of a process calling series of processes, this model stresses on communication between objects. Objects that all self sustained, provide security by encapsulating it's members and providing abstracted interfaces over the functions it performs. OOP's facilitate the following features

1. Inheritance for Code Reuse
2. Abstraction for modularity, maintenance and agility
3. Encapsulation for security and protected
4. Polymorphism for flexibility and interfacing

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

_{Like Discuss Correct / Improve oops oops features Trimax IT Infrastructure & Services Aricent HCL Technologies Tata Consultancy (TCS) Infosys Cognizant (CTS) Capgemini Blue Coat Symantec Deegit Cerner Verizon Ancestry Accenture Accenture India Lexis Nexis Elsevier Overstock Sofi DeCurtis Appirio GlobalLogic Robert Bosch Lexicon IT Teleperformance Ranosys Technologies InfoObjects LoginRadius Pixere GirnarSoft In Time Tec Konstant Infosolutions Axtria Infostretch TatavaSoft E2logyCroods Consolidates Elegant MicroWeb IndiaNIC Infotech Surekha Technologies Amnex InfoTechnologies Wishtree Technologies Apttus Majesco Techsosys Virtusa Gruppo Banca Sella eNoah Volante Technologies Karomi Urjanet Full Creative Uniphore Software Systems Revature Saggezza DXC Technology QBurst Kott Software Petrolink Services RapidValue Solutions Speridian Technologies Fingent Marlabs Ixigo.com Bravura Solutions Amdocs GSPANN Technologies Healthkart Hughes Systique Prospecta Fidelity Mediology Software Ksolves InfoGain Mindfire Solutions Hays R Systems Netrix Technology HexaView PayTM Suncore Microsystem Remaxys ANR Software Impetus Technologies WittyBrains InnovationM Diction Technology Bhavna Corp Bristlecone Fiserv Quovantis Technologies InnovationM Intelligrape Software PayCraft Nearbuy WSE Group Grappus MAQ Software JellyFish Technologies SysArc Infomatix MetricStream Delhivery Atidan Experis NICE Dark Horse IT VizExperts CatalystOne Syntel BlackNGreen InnoEye Technologies Java R&D QA InfoTech HARMAN Eli Global Damco Solutions LensKart 360 Degree FlipKart Egen Solutions AppzCloud Technologies TechAhead Yamaha Motor Solutions Quovantis Technologies Adobe Samsung Noida Lab Lybrate Novelvox HSBC Holdings Fluid AI Nelito System GoldenSource Naaptol Ashtech Infotech Mobicule Future Group Calypso Technology Skillnet Solutions 3i Infotech Nucsoft InteractCRM Aurionpro Solutions Hexaware Technologies Ness Technologies Cigniti Inc ValueLabs Magnaquest Mphasis IVY Comptech Medlife.com ServiceNow Acclaris Reliance Jio Infocomm Bentley Systems Erricson Worldwide Hyland Xpanxion Cerner Codeclouds IT Solutions Procentris Cleocotech International Divergent Soft Lab Endevor IT Solution Impetus Infotech India Bhaskar Technologies SeroSoft Solutions Retina Software General Atomics B3 - Brain Behind Brand Oni Enterprises Amal Infosystems Future Focus Infotech Celcom Technologies Globez Professional Solutions Harjai Computers Pazzo Solutions Data-Core Systems Sampoorna Computer People Trowano Avenues ezyreach.in Sandeep Dwellers Interra Information Technologies Sellcraft Global Solutions RJS Tech Solutions WSE Group Magna India Educiting Technologies Continental Automotive Components India IBM India Asap Info Systems Capgemini Smart Move Career Consultants Aeronube Technologies Skywings Advisors Diverse Lynx ProCreations Kolkata Tickto Solutions Fresher Jobs SMVA Consultants Ixoraa Enterprises ILabz Technology 2Coms Consulting Talent Flix Nat IT Solved Kopal Consultants LLP Rebaca Technologies Techs To Suit Inc Soffront Software eDot Health Solutions MSH Talent Solutions Techathon Networks LLP Vara United Crossover for work Wedoria Technologies Golden Opportunities Minivet System Maitretech JS Tech Alliance BirjaSoft Technologies BirlaSoft AwzPact Technologies and Services MaxGen Technologies Manker Consultancy Services I Quest Consultants ACE Group Seven Consultancy WTM It Limited P R Software DezVen Software Solution Aliens Group EXL Tech Solutions AcompWorld Technosoft Eulogik xtranet technologies Java RnD travelex basic frequent}

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

Q11. What is the difference between ArrayList and LinkedList ?

Core Java

^{admin
info@buggybread.com}

Ans. Underlying data structure for ArrayList is Array whereas LinkedList is the linked list and hence have following differences -

1. ArrayList needs continuous memory locations and hence need to be moved to a bigger space if new elements are to be added to a filled array which is not required for LinkedList.

2. Removal and Insertion at specific place in ArrayList requires moving all elements and hence leads to O(n) insertions and removal whereas its constant O(1) for LinkedList.

3. Random access using index in ArrayList is faster than LinkedList which requires traversing the complete list through references.

4. Though Linear Search takes Similar Time for both, Binary Search using LinkedList requires creating new Model called Binary Search Tree which is slower but offers constant time insertion and deletion.

5. For a set of integers you want to sort using quicksort, it's probably faster to use an array; for a set of large structures you want to sort using selection sort, a linked list will be faster.

Sample Code for ArrayList

Sample Code for LinkedList

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

_{Like Discuss Correct / Improve collections java data structures arraylist linkedlist Deutsche Bank Overstock.com HCL Technologies Infosys EBay The Advisory Board Company Accuity JC Penney Cerner Chase Amazon Deloitte Deegit Tata Consultancy Cognizant (CTS) IBM Accenture Accenture India Mindtree ESRI QwikCilver Solutions TMC Bonds GumGum EMC Yelp Classteacher Learning System FactSet Simply Hired SalesForce Royall & Company Indeed eClinicalWorks TravelClick State Farm Manhattan Associates GoEuro Veeva Systems Ness Technologies Marlabs Rolta Volante Technologies Happiest Minds Technologies Coviam Velocify zanox SimplyHired IDBI Intech Wissen Infotech Nike OnDot PexSupply Pramati Technologies Credit Agricole Mastek Six Dee Telecom Accuity Kellton Tech conduent citrix NEC Technologies General Atomics Basic frequent}

Try 1 Question(s) Test

Basic and Very Frequently asked.

Q12. What is Polymorphism in Java ?

Core Java

^{2016-11-06 09:10:54}

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

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

_{Like Discuss Correct / Improve polymorphism object oriented programming (oops) oops concepts oops concepts Credit Suisse Unbounded Solutions Microsoft Google Purch HCL Technologies Tata Consultancy (TCS) Wipro Mathworks Accenture Accenture India ZonOff ZapCom Addteq Priceline.com Acute Informatics Trimax IT Infrastructure & Services USAA HCL Technologies FDM Group AppEnsure Inov8 TIAA Revature Lockheed Martin ScotiaBank Algorhythm Tech Aurus Xpanxion Bitwise Pune GS Labs Bitwise India CRIF Saggezza Synchrony Micro Focus Mindtree Zycus Capgemini ZapCom Group Infosys Technologies SLK Group Intuit Bangalore Quickr Comviva Technology Altimetrik IDEALINVENT Technologies Kewill coMakeIT Vekomy Technologies Eze Software State Farm Rolta State Street High Radius Cerner TIBCO 3i Infotech Goldman Sachs ITC abhra InteractCRM Polaris Naggaro Siemens Hexaware Technologies Skillnet solutions Logixal Solutions Mumbai Naaptol Mumbai Logixal Solutions NSETECH Mastek Mumbai AppAmplify Noida HexaView Technologies Wipro Wittybrains Software Technologies Meenakshi Noida Eastern Software Systems Noida MediaAgility Gurgaon Daffodil Software Oracle Gurgaon Kellton Tech Gurgaon Bharti Airtel Gurgaon IHS Markit Gurgaon Sinew Gurgaon Grappus Gurgaon Erricson Gurgaon Deloitte Accenture Accenture India Tech Mahindra Patni Computers L&T Infotech Mphasis Mindtree Hexaware Collabera 3i Infotech IGate Kpit Technologies NIIT Technologies Trianz Persistent Systems IT Asset FIA-US VanGuard General Atomics Basic frequent}

Try 2 Question(s) Test

Q13. How does making string as immutable helps with securing information ? How does String Pool pose a security threat ?

Core Java

^{2017-06-22 11:32:57}

Ans. String is widely used as parameter for many java classes, e.g. network connection, opening files, etc. Making it mutable might possess threats due to interception by the other code segment or hacker over internet.

Once a String constant is created in Java , it stays in string constant pool until garbage collected and hence stays there much longer than what's needed. Any unauthorized access to string Pool pose a threat of exposing these values.

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

_{Like Discuss Correct / Improve Security String pool string immutable immutability expert rare}

Very frequently asked across all types of companies.

Q14. Difference between HashMap and Hashtable?

Core Java

^Anonymous

Ans. Hashtable is synchronized whereas HashMap is not.HashMap allows null values whereas Hashtable doesnt allow null values.

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

_{Like Discuss Correct / Improve java collections hashmap map hashtable basic interview question ebay tcs hcl technologies infosys technologies Morgan Stanley Yahoo Q3 Technologies PriceLine Solution Rally Coupang HCL Technologies Tata Consultancy (TCS) Infosys Technologies Accenture Accenture India JPMorgan Chase Priceline.com basic frequent}

Try 2 Question(s) Test

Frequently asked in all types of companies especially Indian Services companies. Frequently asked in CTS (Based on 2 feedback)

Q15. What is the use of hashcode in Java ?

Core Java

^Anonymous

Ans. Hashcode is used for bucketing in Hash implementations like HashMap, HashTable, HashSet etc. The value received from hashcode() is used as bucket number for storing elements. This bucket number is the address of the element inside the set/map. when you do contains() then it will take the hashcode of the element, then look for the bucket where hashcode points to and if more than 1 element is found in the same bucket (multiple objects can have the same hashcode) then it uses the equals() method to evaluate if object are equal, and then decide if contain() is true or false, or decide if element could be added in the set or not.

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

_{Like Discuss Correct / Improve java collections hashcode advanced hashtable Cognizant (CTS) Compro Technologies VigLink Proofpoint Accolite Foot Locker IMC Trading LG Mobile Phones Probity Soft EPPS Infotech AbeBooks LiquidNet Google Girmiti Software Hashcode IT Solutions Aurionpro Solutions Insonix Genpact Trentor CatalystOne Solutions RedBlink Bayatree Infocom Security Weaver Steg Technologies Roshi Software Solutions DreamSoft4u Decipher Zone Softwares Precise Automation & Robotics Componence Dainik Navajyoti Bodacious IT Hub Naggaro intermediate frequent}

Try 1 Question(s) Test

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

Q16. How does volatile affect code optimization by compiler?

Core Java

^{Admin
info@buggybread.com}

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 Embedded security Driver engineer Sokrati expert}

Frequently asked to fresh graduates and less experienced.

Q17. Why do we write public static void main ? Can we use some other syntax too for main ?

Core Java

^{Admin
info@buggybread.com}

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 Cognizant (CTS) Computer Solutions & Software International (CSSI) Telcoinabox IBM Pune basic frequent}

Try 1 Question(s) Test

Q18. What are the advantages and disadvantages of static variables and static methods ?

Core Java

^{Admin
info@buggybread.com}

Ans. Advantages

Can do meta object operations ( like validating something before creating objects , keep count of number of objects )

Can do operations which have nothing to do with objects but still you want them to be tied to Class.

Disadvantages

Commonly used to static variables sometime leads to problems due to access by different objects.

Are not tied to objects so doesn't reflect pure Object Oriented approach.

Needs to be synchronized so as to avoid update conflicts by mutiple objects and threads.

Some limitation in testing as not all frameworks have facility to mock them. Powermock has but Mockito doesnt

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

_{Like Discuss Correct / Improve java static static variables static methods}

Very Frequently asked. Have been asked in HCL Technologies very frequently ( based on 3 feedback ). Among first few questions in many interviews.

Q19. Differences between abstract class and interface ?

Core Java

^{Admin
info@buggybread.com}

Ans. Abstract classes can have both abstract methods ( method declarations ) as well as concrete methods ( inherited to the derived classes ) whereas Interfaces can only have abstract methods ( method declarations ).

A class can extend single abstract class whereas it can implement multiple interfaces.

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

_{Like Discuss Correct / Improve java classes abstract class interfaces GlobalLogic HCL Technologies Tata Consultancy (TCS) Infosys Wipro Mindtree CapitalOne Accenture Accenture India IBM India Infoview Technologies Salesforce AT&T United Health Group (UHG) Verilogue Amazon Expeditors Syntel SalesForce Cornerstone OnDemand Expedia OLA NSF International Copper Mobile Think Future Technologies MorphoTrust Global Healthcare Prodigious Internet Brands SciQuest arvato Systems iCIMS Ideas2IT virtusa polaris Vitech Systems Cognizant (CTS) Speridian Technologies Ojas Innovative Technologies SWC Technology Partners Cricbuzz Jean Martin Capgemini Virtusa ECI Telecom Aptify Crossover ample softech Metanoia software solutions Overstock.com Unic Sol India Experis India Intellect Design Arena Sarathi Softech Transorg Analytics Cibersites India Resource Weaver Indium Software Kone Elevator Merkur Gaming Prama Hikvision Gurucul Solutions e-Zest Solutions ReadMind Info Services Equator Business Solutions basic frequent}

Do you think these are the Best Java Frameworks ?

OpenXava

SPRING MVC

Apache Stripes

Check everything
that is Best in Java

Click Here

Q20. Can you give a real world example of Encapsulation and Abstraction ?

Core Java

^{2016-05-29 13:47:31}

Ans. Car Engine is an example of encapsulation and abstraction. You ignite the car using an interface called starter and least bothered about how the tire actually moves (This is abstraction). The engine encapsulates the complete process to itself only and doesn't allow you to start the other components like the radiator etc ( this is excapsulation )

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

_{Like Discuss Correct / Improve encapsulation object oriented programming (oops) oops concepts abstraction oops oops features java features MAQ Software Daffodil Software Quickstart Global Alliance Global Services InfoStretch Intelligrape Prowareness Support.com Cognizant (CTS) BNT SOFT Clairvoyant TechnoSolutions Suyati Technologies 3DPLM Software Solutions}

Q21. How is string object immutable if we can concat a string to it ?

Core Java

^{2017-08-08 09:50:28}

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.

Q22. Difference between Public, Private, Default and Protected ?

Core Java

^Anonymous

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 basic interview question HCL Technologies Tata Consultancy (TCS) IBM Wipro Deegit Argonne National Laboratory Motorola Mobility Accenture Accenture India Deegit Cerner basic frequent}

Try 1 Question(s) Test

Very Frequently asked to fresh graduates and less experienced. Favorite question in Walk in drives. Frequently asked in Indian Services companies.

Q23. Difference between Overloading and Overriding ?

Core Java

^Anonymous

Ans. Overloading - Similar Signature but different definition , like function overloading.

Overriding - Overriding the Definition of base class in the derived class.

Sample Code for overloading

Sample Code for overriding

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

_{Like Discuss Correct / Improve java oops overloading overriding oops concepts basic interview question PC Technology Cognizant (CTS) Donlen hybris Software RedMane Allerin Technologies Gemalto Allerin Technologies HCL Technologies Tata Consultancy (TCS) Accenture Accenture India Infosys Technologies Polaris United Healthcare India IBM India Xchanging American Express Antra Flipp Computer Sciences Corporation (CSC) Garmin NetSuite Donlen Hudsons Bay Techlogix SevOne Synactive Oodles Technologies FDM Group Marlabs RedMane Technology Faichi Solutions TD Tech Mahindra Shutterfly Luxoft PC Technology CCC Information Services State Farm Raja Software Mastek EPAM Morgan Stanley SummitWorks Sony Citibank Emtec LowerMyBills Consilience Xavor AllState FasTrak AmTrust Financial Walt Disney Ultramain Systems International Turnkey Systems Knoldus Software CA Technologies Amdocs FDM Group Hybris Fidelity United Health Group (UHG) Bluewhale Solutions Pegasystems Revature
Innoplexus Vanguard AptSource Perficient Grapecity Subex QuintilesIMS NimbleUser Expeditors Associate Sapient HR Cloud Summitworks Jabong.com Kony Labs Price Waterhouse Coopers (PWC) basic frequent}

Try 1 Question(s) Test

Q24. What things should be kept in mind while creating your own exceptions in Java?

Core Java

^{Admin
info@buggybread.com}

Ans. All exceptions must be a child of Throwable.

If you want to write a checked exception that is automatically enforced by the Handle or Declare Rule, you need to extend the Exception class.

You want to write a runtime exception, you need to extend the RuntimeException class.

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

_{Like Discuss Correct / Improve java exceptions exception handling user defined exceptions throwable architecture library development technical architect technical lead}

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

Q25. What is a Final Variable ?

Core Java

^Anonymous

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 IBM Goldman Sachs TrueCar Intertek RedMane Antra HCL Technologies Tata Consultancy (TCS) Accenture Accenture India Forte Group Mastercard basic frequent}

Try 1 Question(s) Test

Q26. Can we serialize static variables ?

Core Java

^Anonymous

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 Deloitte intermediate rare}

Try 2 Question(s) Test

Q27. Difference between Vector and ArrayList ?

Core Java

^Anonymous

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 Oracle Lab49 Infosys Wipro Zoho HCL Technologies Tata Consultancy (CTS) BirlaSoft Emory Xplana British Telecom (BT) Apex Systems Capgemini Accenture Accenture India 3dplm Software Solution AppKnox eIntern Landmark Information Group ESystems Orbitz Worldwide HARMAN Starmount iConsultus KARYA Technologies Smart Chip Cuelogic Technologies Kronos Trigent Software Deloitte ACI Worldwide Unisys Tavant Technologies Referance data basic frequent}

Very frequently asked in phone and walk in interviews.

Q28. What are Marker Interfaces ? Name few Java marker interfaces ?

Core Java

^Anonymous

Ans. These are the interfaces which have no declared methods.Serializable and cloneable are marker interfaces.

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

_{Like Discuss Correct / Improve java oops interfaces marker interface serializable clonable Qualtech Consultants Computer Sciences Corporation (CSC) Addteq Infosys Synechron Amdocs JPMorgan Chase Qualtech Consultants Velopsys HCL Technologies Tata Consultancy (TCS) Accenture Accenture India Erricson Technologies Amdocs Ericsson Oracle Avaya Copart Innoplexus Volvo Information Technology intermediate frequent}

Try 1 Question(s) Test

Q29. What are the disadvantages of using arrays ?

Core Java

^{Admin
info@buggybread.com}

Ans. Arrays are of fixed size and have to reserve memory prior to use. Hence if we don't know size in advance arrays are not recommended to use.

Arrays can store only homogeneous elements.

Arrays store its values in contentious memory location. Not suitable if the content is too large and needs to be distributed in memory.

There is no underlying data structure for arrays and no ready made method support for arrays, for every requriment we need to code explicitly

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

_{Like Discuss Correct / Improve java arrays disadvantages of arrays arrays memory arrays vs variables}

Do you think these are the Best Java Frameworks ?

OpenXava

SPRING MVC

Apache Stripes

Check everything
that is Best in Java

Click Here

Q30. Why do we need Thread class even in case we execute thread using runnable interface ?

Core Java

^{Admin
info@buggybread.com}

Ans. Thread class holds the definition of start method ( This is the method that starts execution of new thread and then calls run method within the scope of new thread ). Interfaces don't hold any definition and so does runnable. So it makes it necessary the usage of Thread class , whatever implementation you choose.

When your class extends the thread class, it carries the definition of start method from parent Thread class onto itself and hence new yourClass.start() helps starting a new thread and then executing run method in that new thread scope.

When you implement runnable interface , you are just making it sure to the JVM that you have implemented the required method ( run() ) which the Thread start method will look for upon executing start method.

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

_{Like Discuss Correct / Improve java threads multithreading runnable interface thread class}

Q31. Which of the following Java feature promotes Code Re usability ?

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

Core Java

^Anonymous

Ans. Inheritance

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

_{Like Discuss Correct / Improve java java concepts java features code reusability}

Q32. Why HashTable has been deprecated ?

Core Java

^{2016-07-08 10:01:58}

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

Q33. What are different types of variables a class can have ?

Core Java

^{2017-01-07 16:58:43}

Ans. 1. Method local variables - These are declared and defined within a method ( instance or static methods ) and their scope is limited to the method itself. They are destructed once the execution of method completes. They are stored in stack memory.

2. Instance variables - These are declared as non static variables as part of the class.They are initialized as part of object creation ( constructor ) and are destructed by java's garbage collection mechanism and hence stored in heap.

3. Static variables - These are declared with the static keyword and are part of the class. They are initialized at the time of class loading and are destructed by java's garbage collection mechanism and hence stored in heap.

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

_{Like Discuss Correct / Improve java variables}

Q34. If an Abstract class has only abstract methods, What's the difference between such a class and an interface ?

Core Java

^{2017-05-07 07:26:29}

Ans. Such a class still can have member elements which can be inherited and hence facilitate code reuse. Moreover Abstract class can have non final static elements whereas interfaces are only allowed to have static final elements.

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

_{Like Discuss Correct / Improve abstract class interfaces Tata Consultancy (TCS) Infosys Basic}

Q35. When we say final x = 10, is the reference final or the value ?

Core Java

^{2017-07-29 13:27:04}

Ans. final keyword have meaning only to referenced and not the value. It means that the specified reference cannot be dereferenced. It doesn't control the value assigned to the memory that's being referenced. This is the reason that final object references doesn't mean that the object is immutable but means that the reference cannot be changed to point to new object.

In case of primitive types too, when we assign a reference to another, values are passed and not the object reference, and hence a new placeholder is created in memory with the same value. That is why final to that context means that you cannot change the assigned memory and there is no way we can have that memory place have another value.

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

_{Like Discuss Correct / Improve final keyword final variables references}

Q36. When are static variables loaded in memory ?

Core Java

^Anonymous

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}

Q37. Can we use null as a key for a map collection ?

Core Java

^Anonymous

Ans. Yes , for HashMap. HashMap implements Map interface. HashMap allows one null key and any number of null values.

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

_{Like Discuss Correct / Improve java collections hashmap map hashtable yes-no BlackBerry}

Q38. Difference between Abstract and Concrete Class ?

Core Java

^Anonymous

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 basic interview question Goldman Sachs basic frequent}

Frequently asked question for intermediate developers.

Q39. What is Volatile keyword used for ?

Core Java

^Anonymous

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 ABC Ltd Ciena Xchanging Square Infoview Technologies HCL Technologies EPAM GrubHub TeleMessage TRUSTe Informatica Square Medidata Solutions Yellow Pages eQ Technologic Sutra Analytics CustomerXPs Globant BB Holdings Rakuten Booking.com BlackRock Qualcomm LSI Corporation ARM Holdings SpaceX Toshiba Peapod Amadeus Apptio Tivo EchoStar HomeAway Syscom Technologies Aversan Symantec Samsung India Axtria Qualcomm CGI Group TrustArc Square intermediate frequent}

Try 1 Question(s) Test

Do you think these are the Best Java Frameworks ?

OpenXava

SPRING MVC

Apache Stripes

Check everything
that is Best in Java

Click Here

Q40. What is the use of Transient Keyword ?

Core Java

^Anonymous

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 Cognizant (CTS) The Advisory Board Company HCL Technologies Tata Consultancy (TCS) Accenture Accenture India Mphasis L&T Infotech Patni SecurView Morgan Stanley American Express Natrix Technology Intellect Design Arena Calypso Technology Deloitte CRIF eQ Technologic SQLI J-Labs U.S. Bank US Bank Next Insurance Personal Capital Global Healthcare Exchange Mastek Toshiba Zilingo Tivo OnDot Systems Infinera NXP Semiconductors Walmart Specbee Autosar Finoit TechnoGen Samsung India intermediate frequent}

Try 2 Question(s) Test

Search Interview Questions

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