Interview Questions and Answers - Expert Level | Search Java Interview Question

Interview Questions and Answers - Expert Level - 77 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

Q3. Which are the different segments of memory ?

Core Java

^Anonymous

Ans. 1. Stack Segment - Contains primitives, Class / Interface names and references.

2. Heap Segment - Contains all created objects in runtime, objects only plus their object attributes (instance variables), Static variables are also stored in heap.

3. Code Segment - The segment where the actual compiled Java bytecodes resides when loaded

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

_{Like Discuss Correct / Improve java memory memory management stack memory heap memory code segment memory advanced NX Developer Velocity Commvault eBizprise Taiwan Tata Consultancy (TCS) Nakisa HCL Technologies Blue Coat Symantec expert frequent}

Try 6 Question(s) Test

Q4. 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}

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

Q5. 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}

Q6. 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

Q7. 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}

Q8. 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}

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

Q9. 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}

Do you think these are the Best Java Frameworks ?

OpenXava

SPRING MVC

Apache Stripes

Check everything
that is Best in Java

Click Here

Not frequently asked as it was introduced with Java 8.

Q10. Difference between final and effectively final ? Why is effectively final even required ?

Core Java

^{Admin
info@buggybread.com}

Ans. Final variable means a variable that has been declared final and hence cannot be de referenced after initialization. Effective final means a variable that has not been declared final but haven't been reassigned the value after initialization.

First is the regulation that restricts the reassignment and will raise a compilation error if we try to do so. Second is the outcome without the restriction.

Effective Final is the eventual treatment of the variable that is required for many features. For eq - Java 8 requires that local variables referenced from a lambda expression must be final or effectively final.It means all local referenced from lambda expressions must be such that their value shouldn't be changed after initialization whether declared final or not.

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

_{Like Discuss Correct / Improve java java8 java 8 final effective final final vs effective final lambda expressions expert}

Try 2 Question(s) Test

Q11. Can we declare static variables as transient ?

Core Java

^{2017-01-12 11:12:48}

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 HCL Technologies expert rare}

Try 1 Question(s) Test

Q12. Can constructors be synchronized in Java ?

Core Java

^Anonymous

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 Tieto expert rare}

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

Q13. What is database deadlock ? How can we avoid them?

Database

^{Admin
info@buggybread.com}

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 MSCI Vudu Bank Of America Sears BlueCoat Symantec expert frequent}

Q14. Difference between Predicate, Supplier and Consumer ?

Core Java

^{Admin
info@buggybread.com}

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 expert}

Q15. Which String class does not override the equals() and hashCode() methods, inheriting them directly from class Object?

Core Java

^Anonymous

Ans. java.lang.StringBuffer.

Sample Code for StringBuffer

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

_{Like Discuss Correct / Improve java object class stringbuffer expert rare}

Q16. What one should take care of, while serializing the object?

^Anonymous

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}

Q17. Are constructors inherited? Can a subclass call the parent's class constructor? When?

Core Java

^Anonymous

Ans. You cannot inherit a constructor. That is, you cannot create a instance of a subclass using a constructor of one of it's superclasses. One of the main reasons is because you probably don't want to override the superclasses constructor, which would be possible if they were inherited. By giving the developer the ability to override a superclasses constructor you would erode the encapsulation abilities of the language.

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

_{Like Discuss Correct / Improve java oops constructor inheritence expert rare}

Try 1 Question(s) Test

Q18. Difference between Factory and Abstract Factory Design Pattern ?

Design

^Anonymous

Ans. Factory Pattern deals with creation of objects delegated to a separate factory class whereas Abstract Factory patterns works around a super-factory which creates other factories.

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

_{Like Discuss Correct / Improve java design pattern factory design pattern abstract factory design pattern technical lead expert}

Q19. Can we override compareTo method for Enumerations ?

Core Java

^{Admin
info@buggybread.com}

Ans. No. compareTo method is declared final for the Enumerations and hence cannot be overriden. This has been intentionally done so that one cannot temper with the sorting order on the Enumeration which is the order in which Enum constants are declared.

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

_{Like Discuss Correct / Improve java compareto final methods enum enumeration expert}

Do you think these are the Best Java Frameworks ?

OpenXava

SPRING MVC

Apache Stripes

Check everything
that is Best in Java

Click Here

Q20. 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

Q21. Why do member variables have default values whereas local variables don't have any default value ?

Core Java

^Anonymous

Ans. member variable are loaded into heap, so they are initialized with default values when an instance of a class is created. In case of local variables, they are stored in stack until they are being used.

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

_{Like Discuss Correct / Improve java jvm memory management variables stack memory heap memory default values expert}

Q22. Will this code give error if i try to add two heterogeneous elements in the arraylist. ? and Why ?

List list1 = new ArrayList<>();
list1.add(5);
list1.add("5");

^{Admin
info@buggybread.com}

Ans. If we don't declare the list to be of specific type, it treats it as list of objects.

int 1 is auto boxed to Integer and "1" is String and hence both are objects.

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

_{Like Discuss Correct / Improve java collections arraylist list autoboxing wrapper classes expert rare}

Q23. Difference between static vs. dynamic class loading?

Core Java

^{Admin
info@buggybread.com}

Ans. static loading - Classes are statically loaded with Java new operator.

dynamic class loading - Dynamic loading is a technique for programmatically invoking the functions of a class loader at run time.

Class.forName (Test className);

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

_{Like Discuss Correct / Improve java jvm memory management class loaders classloaders static class loading static loading dynamic class loading dynamic loading IBM JDA expert frequent}

Q24. What is PermGen or Permanent Generation ?

Core Java

^{Admin
info@buggybread.com}

Ans. The memory pool containing all the reflective data of the java virtual machine itself, such as class and method objects. With Java VMs that use class data sharing, this generation is divided into read-only and read-write areas. The Permanent generation contains metadata required by the JVM to describe the classes and methods used in the application. The permanent generation is populated by the JVM at runtime based on classes in use by the application. In addition, Java SE library classes and methods may be stored here.

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

_{Like Discuss Correct / Improve java jvm memory management permgen permanent generation advanced architecture JP Morgan SAP Informatica Credit Agricole EXFO EMC Credit Agricole Cognizant (CTS) JP Morgan expert}

Q25. What is metaspace ?

Core Java

^{Admin
info@buggybread.com}

Ans. The Permanent Generation (PermGen) space has completely been removed and is kind of replaced by a new space called Metaspace. The consequences of the PermGen removal is that obviously the PermSize and MaxPermSize JVM arguments are ignored and you will never get a java.lang.OutOfMemoryError: PermGen error.

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

_{Like Discuss Correct / Improve java jvm memory management permgen permanent generation metaspace advanced architecture expert}

Q26. Can we call the garbage collector explicitly ?

Core Java

^{Admin
info@buggybread.com}

Ans. Yes, We can call garbage collector directly but it doesn't guarantees that the gc will start executing immediately. This gc( ) method appears in both Runtime and System classes of java.lang package.

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

_{Like Discuss Correct / Improve java garbage collection java memory management jvm gc yes no Hewlett Packard (HP) eGain Egen Solutions Computer Sciences Corporation (CSC) expert}

Try 1 Question(s) Test

Q27. what is covariant return type?

Core Java

^{Admin
info@buggybread.com}

Ans. co-variant return type states that return type of overriding method can be subtype of the return type declared in method of superclass. it has been introduced since jdk 1.5

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

_{Like Discuss Correct / Improve java oops inheritence overriding covariant return type jdk5 advanced Hewlett Packard (HP) The Systems Group Evergent expert}

Q28. Why String is popular HashMap key in Java?

Core Java

^{Admin
info@buggybread.com}

Ans. Since String is immutable, its hashcode is cached at the time of creation and it doesnt need to be calculated again. This makes it a great candidate for key in a Map and its processing is fast than other HashMap key objects. This is why String is mostly used Object as HashMap keys.

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 hashmap immutable immutability hashcode hash code advanced TD Bank HCL Technologies expert frequent}

Q29. What does String intern() method do?

Core Java

^{Admin
info@buggybread.com}

Ans. intern() method keeps the string in an internal cache that is usually not garbage collected.

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

_{Like Discuss Correct / Improve java string class string intern method garbage collection advanced Polaris Netflix expert}

Do you think these are the Best Java Frameworks ?

OpenXava

SPRING MVC

Apache Stripes

Check everything
that is Best in Java

Click Here

Q30. How substring() method of String class create memory leaks?

Core Java

^{Admin
info@buggybread.com}

Ans. substring method would build a new String object keeping a reference to the whole char array, to avoid copying it. Hence you can inadvertently keep a reference to a very big character array with just a one character string.

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

_{Like Discuss Correct / Improve java string class string substring memory leaks jvm memory management advanced architecture technical architect technical lead expert}

Q31. What are Default Methods ?

Core Java

^{Admin
info@buggybread.com}

Ans. With Java 8, We can provide method definitions in the Interfaces that gets carried down the classes implementing that interface in case they are not overridden by the Class. Keyword "default" is used to mark the default method.

Sample Code for interface default

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

_{Like Discuss Correct / Improve java java8 default methods DataArt Expeditors Wipro GoodData Infosys Technologies sharp software development Ensure support services expert frequent}

Q32. Does use of Final class enforces composition over Inheritance in Java ?

Core Java

^{2018-07-16 06:49:53}

Ans. Yes, to a certain extent. But the objective for Final class could be beyond just enforcing composition as certain classes might have been created without inheritance or composition in mind.

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

_{Like Discuss Correct / Improve final class composition object oriented programming (oops) oops concepts inheritance object oriented programming (oops) oops concepts composition object oriented programming (oops) oops concepts vs inheritance object oriented programming (oops) oops concepts expert}

Q33. What could be the reasons for restricting inheritance using final class ?

Core Java

^{2018-07-16 06:52:00}

Ans. 1. Enforcing composition over inheritance
2. Restricting overriding of certain methods
3. Final methods are faster than regular instance methods
4. Enforcing Immutability

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

_{Like Discuss Correct / Improve final class reasons for final class restricting inheritance object oriented programming (oops) oops concepts expert}

Q34. What will happen if there are no interfaces in Java ?

Core Java

^{2018-12-11 16:16:37}

Ans. Abstract classes can take care of that to a certain extent. Though they are little heavier than Interfaces but An abstract class with all abstract methods and no instance variables will be able to help with everything that currently an interface does.

The only problem is that a class can only extend one class whereas it can implements multiple interfaces and that is the reason Interfaces were introduced in Java, i.e to get over the problem of multiple inheritance.

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

_{Like Discuss Correct / Improve interfaces expert}

Q35. Difference between long.Class and Long.TYPE ?

^Anonymous

Ans. They both represent the long primitive type. They are exactly the same.

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

_{Like Discuss Correct / Improve java data types long.Class long.TYPE advanced expert rare}

Q36. Which memory segment loads the java code ?

Core Java

^Anonymous

Ans. Code segment.

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

_{Like Discuss Correct / Improve memory java memory management code segment code segment memory expert rare}

Q37. Can a lock be acquired on a class ?

^Anonymous

Ans. Yes, a lock can be acquired on a class. This lock is acquired on the class's Class object.

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

_{Like Discuss Correct / Improve java scheduling threads multi threading expert rare}

Q38. Difference between Factory and Builder Design Pattern ?

Design

^Anonymous

Ans. Builder pattern is the extension of Factory pattern wherein the Builder class builds a complex object in multiple steps.

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

_{Like Discuss Correct / Improve java design pattern factory design pattern builder design pattern Epam expert}

Q39. Difference between Proxy and Adapter ?

Design

^Anonymous

Ans. Adapter object has a different input than the real subject whereas Proxy object has the same input as the real subject. Proxy object is such that it should be placed as it is in place of the real subject.

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

_{Like Discuss Correct / Improve java design pattern proxy adapter expert}

Do you think these are the Best Java Frameworks ?

OpenXava

SPRING MVC

Apache Stripes

Check everything
that is Best in Java

Click Here

Q40. Difference between Adapter and Facade ?

Design

^Anonymous

Ans. The Difference between these patterns in only the intent. Adapter is used because the objects in current form cannot communicate where as in Facade , though the objects can communicate , A Facade object is placed between the client and subject to simplify the interface.

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

_{Like Discuss Correct / Improve java design pattern adapter facade expert}

Search Interview Questions

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