Java - Interview Questions and Answers for 'Core Java' | Search Java Interview Question - javasearch.buggybread.com
Javasearch.buggybread.com
Share

Search Java Interview Questions


 2098 questions in repository.
 There are more than 200 unanswered questions.
Click here and help us by providing the answer.
Label / Company      Label / Company / Text

   



Interview Questions and Answers for 'Core Java' - 918 question(s) found - Order By Newest

next 100
Very Very frequently asked. Among the first few questions in almost all interviews.Among Top 5 frequently asked questions.
  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

 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     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      basic        frequent

Try 6 Question(s) Test


Advanced level question. Frequently asked in High end product companies. Frequently asked in Cognizant ( Based on 2 feedbacks )
  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   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      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      basic        frequent

Try 3 Question(s) Test


Frequently asked to fresh graduates and less experienced developers. Among the first few questions in many interviews.
  Q4. What are the difference between composition and inheritance in Java?Core Java
Admin
info@buggybread.com
Ans. Composition - has-a relationship between classes.
Inheritance - is-a relationship between classes.

Composition - Composing object holds a reference to composing classes and hence relationship is loosely bound.
Inheritance - Derived object carries the base class definition in itself and hence its tightly bound.

Composition - Used in Dependency Injection
Inheritance - Used in Runtime Polymorphism

Composition - Single class objects can be composed within multiple classes.
Inheritance - Single class can only inherit 1 Class.

Composition - Its the relationship between objects.
Inheritance - Its the relationship between classes.

  Sample Code for inheritance

  Sample Code for composition

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

   Like      Discuss      Correct / Improve     java   java concepts   inheritance   composition   inheritance vs composition     HCL Technologies  Tata Consultancy (TCS)  Infosys  Amazon  Source Intelligence  News UK  Starmount  MapQuest  SalesForce  Expedia  Deegit  JP Morgan  Canva  Todle  Yodle  Berkley Net  Help Scout  Partners HealthCare  Doximity  Commvault  Heroku  Starmount  Help.com  healthcare system  TU Kaiserslautern      basic        frequent

Try 5 Question(s) Test


 Q5. 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)      expert        frequent

Try 6 Question(s) Test


 Q6. Why do we need Inner classes ? Cant we just work with outer classes wherever we implement Inner classes ?Core Java
Admin
info@buggybread.com
Ans. Yes, we can substitute outer classes wherever we need to have inner classes but Inner classes have advantage in certain cases and hence preferred -

Ease - Why to implement a class outside if its objects are only intended to be part of an outer object. Its easy to define the class within another class if the use is only local.

Protection - Making a call an outer exposes a threat of it being used by any of the class. Why should it be made an outer class if its object should only occur as part of other objects.

For example - You may like to have an class address whose object should have a reference to city and by design thats the only use of city you have in your application. Making Address and City as outer class exposes City to any of the Class. Making it an inner class of Address will make sure that its accessed using object of Address.

  Sample Code for 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   objects   technical lead      intermediate

Try 1 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( )

 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      expert


 Q8. What are points to consider in terms of access modifier when we are overriding any method?Core Java
Admin
info@buggybread.com
Ans. 1. Overriding method can not be more restrictive than the overridden method.

reason : in case of polymorphism , at object creation jvm look for actual runtime object. jvm does not look for reference type and while calling methods it look for overridden method.

If by means subclass were allowed to change the access modifier on the overriding method, then suddenly at runtime when the JVM invokes the true objects version of the method rather than the reference types version then it will be problematic

2. In case of subclass and superclass define in different package, we can override only those method which have public or protected access.

3. We can not override any private method because private methods can not be inherited and if method can not be inherited then method can not be overridden.

  Sample Code for Overriding

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

   Like      Discuss      Correct / Improve     java   overriding   access specifier   inheritence   oops   polymorphism   runtime polymorphism     Genpact

Try 2 Question(s) Test


 Q9. What are different ways to create String Object? Explain.Core Java
Admin
info@buggybread.com
Ans.
String str = new String("abc");
String str1 = "abc";


When we create a String using double quotes, JVM looks in the String pool to find if any other String is stored with same value. If found, it just returns the reference to that String object else it creates a new String object with given value and stores it in the String pool.

When we use new operator, JVM creates the String object but dont store it into the String Pool. We can use intern() method to store the String object into String pool or return the reference if there is already a String with equal value present in the pool.

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

   Like      Discuss      Correct / Improve     java   string class   string   jvm   memory management   string pool     GuideWire  NTT Data  Fractal Analytics      basic        frequent

Try 3 Question(s) Test



Do you think these are the Best Java Frameworks ?

OpenXavaSPRING MVCApache StripesCheck everything
that is Best in Java

Click Here



 Q10. 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      basic        frequent


 Q11. What is the difference between declaration, instantiation and initialization ?Core Java2016-05-26 14:17:48

Ans. Declaration is intimation to the compiler about the nature of Data a reference is going to hold.

For example - List myList;

Instantiation is reservation of memory.

For example

myList = new ArrayList();

Initialization or construction is setting the default values for member elements.

For example

myList = new ArrayList(mySet);

** Example 2nd is both for instantiation as well as initialization. The only difference is that 2nd will initialized the member elements to their default values whereas 3rd will initialized it with the elements from set.


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

   Like      Discuss      Correct / Improve     declaration   instantiation   initialization   construction      basic        frequent


 Q12. What are the common uses of "this" keyword in java ?Core Java
Anonymous
Ans. "this" keyword is a reference to the current object and can be used for following -

1. Passing itself to another method.

2. Referring to the instance variable when local variable has the same name.

3. Calling another constructor in constructor chaining.

  Sample Code for this keyword

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

   Like      Discuss      Correct / Improve     java   this   object reference   constructor chaining      intermediate        rare

Try 3 Question(s) Test


 Q13. Does garbage collection guarantee that a program will not run out of memory?Core Java
Anonymous
Ans. Garbage collection does not guarantee that a program will not run out of memory. It is possible for programs to use up memory resources faster than they are garbage collected. It is also possible for programs to create objects that are not subject to garbage collection

 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   advanced

Try 1 Question(s) Test


Frequently asked.
 Q14. If you are given a choice to use either ArrayList and LinkedList, Which one would you use and Why ?Core Java
Admin
info@buggybread.com
Ans. ArrayList are implemented in memory as arrays and hence allows fast retrieval through indices but are costly if new elements are to be inserted in between other elements. LinkedList allows for constant-time insertions or removals using iterators, but only sequential access of elements
1. Retrieval - If Elements are to be retrieved sequentially only, Linked List is preferred.
2. Insertion - If new Elements are to be inserted in between other elements , Array List is preferred.
3. Search - Binary Search and other optimized way of searching is not possible on Linked List.
4. Sorting - Initial sorting could be pain but lateral addition of elements in a sorted list is good with linked list.
5. Adding Elements - If sufficiently large elements needs to be added very frequently ,Linked List is preferable as elements don't need consecutive memory location.

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

   Like      Discuss      Correct / Improve     java   collections   list   arraylist   linkedlist   difference between   architecture   data structure   ebay      basic        frequent

Try 2 Question(s) Test


  Q15. 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      expert        frequent

Try 1 Question(s) Test


 Q16. Which of the following combination of keywords is illegal in Java ?

a. static and transient
b. transient and final
c. static and synchronized
d. abstract and final
Core Java
Anonymous
Ans. abstract and final

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

   Like      Discuss      Correct / Improve     java   java keywords     VirtusaPolaris  IVTL InfoView Technologies      basic


 Q17. What are different types of classes ?Core Java

Ans. There are different verticals in which Java Classes can be classified.

1. Access - Public , Private , default or Protected.

2. Packaging - System, library or User Defined

3. Structure - Outer or Inner

4. Object Derivation - Abstract Class or Concrete Class.

5. Object Creation - Normal, Singleton , Doubleton , Immutable or Enum.

6. Functionality - String , Util , Stream etc.

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

   Like      Discuss      Correct / Improve     classes   different types of classes     iFactor

Try 1 Question(s) Test


 Q18. How can we run a java program without making any object?Core Java
Anonymous
Ans. By putting code within static method. With Java 6 and earlier versions, even static block can be used.

  Sample Code for static block

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

   Like      Discuss      Correct / Improve     java   oops   static   static method   static block     American Express  Cognizant (CTS)      basic        frequent

Try 1 Question(s) Test


Very frequently asked to Fresh graduates.
  Q19. 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   abstraction   basic interview question     Synechron  Amazon  HCL Technologies  Tata Consultancy (TCS)  Wipro  Infosys Technologies  3DPLM Software Solutions      basic        frequent

Try 2 Question(s) Test



Do you think these are the Best Java Frameworks ?

OpenXavaSPRING MVCApache StripesCheck everything
that is Best in Java

Click Here



 Q20. Can we use both "this()" and "super()" in a constructor ?Core Java
Anonymous
Ans. No, because both this and super should be the first statement.

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

   Like      Discuss      Correct / Improve     java   oops  this   super   constructor      intermediate        rare

Try 2 Question(s) Test


Very frequently asked. Favorite question in Walk in Drive of many Indian service companies. Frequently asked in HCL Technologies.
  Q21. 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  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      basic        frequent

Try 4 Question(s) Test


 Q22. Why every object constructor automatically call super() in Object before its own constructors?Core Java
Admin
info@buggybread.com
Ans. Derived object carries the body of its class as well as the body of the parent class. Its body ( member elements ) is initialized using its own class constructor whereas the body ( member elements ) carried from the parent class are initialized using super class constructor. So In order to initialize the elements of the parent class before its own elements are even initialized, super is called.

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

   Like      Discuss      Correct / Improve     java   oops   constructor   super   inheritance   inheritence     Itech      intermediate


 Q23. Describe what happens when an object is created in Java ?Core Java
Anonymous
Ans. 1. Memory is allocated from heap to hold all instance variables and implementation-specific data of the object and its superclasses. Implemenation-specific data includes pointers to class and method data.
2. The instance variables of the objects are initialized to their default values.
3. The constructor for the most derived class is invoked. The first thing a constructor does is call the constructor for its superclasses. This process continues until the constructor for java.lang.Object is called,as java.lang.Object is the base class for all objects in java.
4. Before the body of the constructor is executed, all instance variable initializers and initialization blocks are executed. Then the body of the constructor is executed. Thus, the constructor for the base class completes first and constructor for the most derived class completes last.

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

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


Very frequently asked. Favorite question in Walk in Drive of many Indian service companies.
  Q24. Difference between TreeMap and HashMap ?Core Java
Anonymous
Ans. They are different the way their elements are stored in memory. TreeMap stores the Keys in order whereas HashMap stores the key value pairs randomly.

  Sample Code for treemap

  Sample Code for hashmap

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

   Like      Discuss      Correct / Improve     java   collections   map   treemap   hashmap     Amber Road  CTS (Cognizant)  ION Trading  DataMetica  Accenture  The Advisory Board Company  BidGely  Infosys  Tata Consultancy (TCS)  HCL Technologies  Wipro  Booking.com  MakeMyTrip  Garena Online  Garmin  ION Trading  Accuity  Palantir Technologies  Books International  Wealthfront  Marin Software  Garmin  IBM  Global Logic  Fiserv  Cumulus Systems  CCTS  UST Global      basic        frequent

Try 1 Question(s) Test


Very frequently asked across all types of companies.
  Q25. 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 India  JPMorgan Chase  Priceline.com      basic        frequent

Try 2 Question(s) Test


 Q26. What will this code print ?

String a = new String ("TEST");
String b = new String ("TEST");
if(a == b) {
System.out.println ("TRUE");
} else {
System.out.println ("FALSE");
}
Core Java
Anonymous
Ans. FALSE. == operator compares object references, a and b are references to two different objects, hence the FALSE. .equals method is used to compare string object content.

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

   Like      Discuss      Correct / Improve     string   string class   java   ==   object references   coding      basic        frequent

Try 1 Question(s) Test


Advanced level question usually asked in High end product companies. Have been asked in Google and Amazon (Based on 1 Feedback)
  Q27. Describe, in general, how java's garbage collector works ?Core Java
Anonymous
Ans. The Java runtime environment deletes objects when it determines that they are no longer being used. This process is known as garbage collection. The Java runtime environment supports a garbage collector that periodically frees the memory used by objects that are no longer needed. The Java garbage collector is a mark-sweep garbage collector that scans Java dynamic memory areas for objects, marking those that are referenced. After all possible paths to objects are investigated, those objects that are not marked (i.e. are not referenced) are known to be garbage and are collected.

 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   advanced     LinkedIn  Infosys  Google  Netflix  Amazon  Huawei Technologies  JP Morgan  enGenius  CitiusTech  Goldman Sachs  Bank Of America India  Salesforce  Addteq  Criteo  Capgemini  Horizon Solutions      intermediate        frequent

Try 4 Question(s) Test


Frequently asked. Favorite question in Walk in Drive of many Indian service companies.
  Q28. What are the methods of Object Class ?Core Java
Anonymous
Ans. clone() - Creates and returns a copy of this object.

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

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

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

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

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

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

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

   Like      Discuss      Correct / Improve     java   oops   object class     Capgemini  NIIT Technologies   Virtusa  Goldman Sachs  PwC  Citi  Expeditors  SoftFluent  LinkedIn  Amadeus  Navteq  PLC Systems  Axtria Associate  Netcracker Technology  Altisource      basic        frequent

Try 1 Question(s) Test


 Q29. 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   string pool   garbage collection   advanced     General Motors  Amura Marketing Technologies  Bloomberg  Innovive      Expert



Do you think these are the Best Java Frameworks ?

OpenXavaSPRING MVCApache StripesCheck everything
that is Best in Java

Click Here



Very frequently asked. Favorite question in Walk in Drive of many Indian service companies.
  Q30. 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  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      Basic        frequent

Try 1 Question(s) Test


Not frequently asked as it was introduced with Java 8.
 Q31. 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


Frequently asked to fresh graduates and less experienced.
 Q32. 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 and using class name only , void means it doesnt return anything , String args[] is the array of argument that this method receives.

2. If I use Main , it will compile correctly as Java will treat it as just another method but 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


 Q33. 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


 Q34. Which keyword is used to provide explicit access of a code block to single thread ?

a. Transient
b. Final
c. Explicit
d. Synchronized
Core Java
Anonymous
Ans. Synchronized

  Sample Code for Synchronized

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

   Like      Discuss      Correct / Improve     java   threads   multithreading     Infoview  HCL Technologies      basic


 Q35. Enums cannot be declared ..

a. private
b. public
c. static
d. final
Core Java
Anonymous
Ans. final

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

   Like      Discuss      Correct / Improve     java   enum


 Q36. Can you give a real world example of Encapsulation and Abstraction ?Core Java2016-05-29 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  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


 Q37. What are concepts introduced with Java 5 ?Core Java
Anonymous
Ans. Generics , Enums , Autoboxing , Annotations and Static Import.

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

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

Try 1 Question(s) Test


  Q38. What is a String Pool ?Core Java
Anonymous
Ans. String pool (String intern pool) is a special storage area in Java heap. When a string is created and if the string already exists in the pool, the reference of the existing string will be returned, instead of creating a new object and returning its reference.

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

   Like      Discuss      Correct / Improve     java   oops   string   string class   string pool   heap memory     SAS Institute  Ariba  GuideWire  Harbinger  Oracle  Virtusa  Knoa  Polaris  GuideWire  HCL Technologies  Tata Consultancy (TCS)  Infosys  Technologent  MphasiS  Harbinger Group  Kony  Evergent  NTT Data  VMware  Markit  Ariba  Tech Mahindra  Bureau Veritas  InfoStretch  PTC Software  Mindtree  Centre for Internet and Society (CIS)  Trimax IT Infrastructure & Services      intermediate        frequent

Try 2 Question(s) Test


Very frequently asked. Usually asked in different variants like Diff between StringBuffer , String Builder ; Difference between StringBuilder and String class; Choice between these classes etc.
  Q39. What is the difference between StringBuffer and String class ?Core Java
Anonymous
Ans. A string buffer implements a mutable sequence of characters. A string buffer is like a String, but can be modified. At any point in time it contains some particular sequence of characters, but the length and content of the sequence can be changed through certain method calls.

The String class represents character strings. All string literals in Java programs, such as "abc" are constant and implemented as instances of this class; their values cannot be changed after they are created.

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

   Like      Discuss      Correct / Improve     java   string   stringbuffer   frequently asked     BlackRock  Synechron  RedMane Technology  Velopsys Technologies   American Express  Sophos  QualiTest  ebay  Infosys Technologies      basic        frequent

Try 1 Question(s) Test



Do you think these are the Best Java Frameworks ?

OpenXavaSPRING MVCApache StripesCheck everything
that is Best in Java

Click Here



 Q40. 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


Very Frequently asked to fresh graduates and less experienced. Favorite question in Walk in drives.
  Q41. 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 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


  Q42. 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  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


 Q43. Difference between object instantiation and construction ?Core Java
Anonymous
Ans. Though It's often confused with each other, Object Creation ( Instantiation ) and Initialization ( Construction ) are different things in Java. Construction follows object creation.

Object Creation is the process to create the object in memory and returning its handler. Java provides New keyword for object creation.

Initialization is the process of setting the initial / default values to the members. Constructor is used for this purpose. If we don't provide any constructor, Java provides one default implementation to set the default values according to the member data types.

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

   Like      Discuss      Correct / Improve     java   oops   constructor   object instantiation


 Q44. Can we access instance variables within static methods ?Core Java
Anonymous
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     Oracle


Very frequently asked in phone and walk in interviews.
  Q45. 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 Technologies  Amdocs  Ericsson  Oracle  Avaya  Copart  Innoplexus  Volvo Information Technology      intermediate        frequent

Try 1 Question(s) Test


Advanced level question. Recently asked in few Indian service companies ( Based on 3 inputs )
 Q46. What are various types of Class loaders used by JVM ?Core Java
Admin
info@buggybread.com
Ans. Bootstrap - Loads JDK internal classes, java.* packages.

Extensions - Loads jar files from JDK extensions directory - usually lib/ext directory of the JRE

System - Loads classes from system classpath.

 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   bootstrap   extensions   system  classloaders   advanced   technical lead   technical architect     Deloitte  Mindtree  Accenture  Synechron  IBM


 Q47. Difference Between this() and super() ?
Core Java
Admin
info@buggybread.com
Ans. 1.this is a reference to the current object in which this keyword is used whereas super is a reference used to access members specific to the parent Class.

2.this is primarily used for accessing member variables if local variables have same name, for constructor chaining and for passing itself to some method whereas super is primarily used to initialize base class members within derived class constructor.

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

   Like      Discuss      Correct / Improve     java   oops   class   objects   inheritence   constructor   this   super

Try 1 Question(s) Test


 Q48. 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


 Q49. What is a stream and what are the types of Streams and classes of the Streams?Core Java
Admin
info@buggybread.com
Ans. A Stream is an abstraction that either produces or consumes information. There are two types of Streams :

Byte Streams: Provide a convenient means for handling input and output of bytes.

Character Streams: Provide a convenient means for handling input & output of characters.

Byte Streams classes: Are defined by using two abstract classes, namely InputStream and OutputStream.

Character Streams classes: Are defined by using two abstract classes, namely Reader and Writer.

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

   Like      Discuss      Correct / Improve     java   file io   streams   byte stream   character stream



Do you think these are the Best Java Frameworks ?

OpenXavaSPRING MVCApache StripesCheck everything
that is Best in Java

Click Here



 Q50. What are the Disadvantages of using Collection Classes over Arrays ?Core Java
Admin
info@buggybread.com
Ans. Collections can only hold objects, It can't hold primitive data types.

Collections have performance overheads as they deal with objects and offer dynamic memory expansion. This dynamic expansion could be a bigger overhead if the collection class needs consecutive memory location like Vectors.

Collections doesn't allow modification while traversal as it may lead to concurrentModificationException.

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

   Like      Discuss      Correct / Improve     java   collections   collections classes   disadvantages of collections over arrays   collections vs arrays


 Q51. What is Generalization and Specialization in terms of casting ?Core Java
Admin
info@buggybread.com
Ans. Generalization or UpCasting is a phenomenon where a sub class is prompted to a super class, and hence becomes more general. Generalization needs widening or up-casting. Specialization or DownCasting is a phenomenon where a super class is narrowed down to a sub class. Specialization needs narrowing or down-casting.

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

   Like      Discuss      Correct / Improve     java   data types   casting   up casting   downcasting   generalization   specialization     Tata Consultancy (TCS)  VirtusaPolaris


Advanced level question usually asked to senior developers , leads and architects.
 Q52. 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


 Q53. How compiler handles the exceptions in overriding ?Core Java
Admin
info@buggybread.com
Ans. 1)The overriding methods can throw any runtime Exception , here in the case of runtime exception overriding method (subclass method) should not worry about exception being thrown by superclass method.

2)If superclass method does not throw any exception then while overriding, the subclass method can not throw any new checked exception but it can throw any runtime exception

3) Different exceptions in java follow some hierarchy tree(inheritance). In this case , if superclass method throws any checked exception , then while overriding the method in subclass we can not throw any new checked exception or any checked exception which are higher in hierarchy than the exception thrown in superclass method

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

   Like      Discuss      Correct / Improve     java   overriding   exceptions   inheritence   inheritance   oops


 Q54. Similarity and Difference between static block and static method ?Core Java
Admin
info@buggybread.com
Ans. Both belong to the class as a whole and not to the individual objects. Static methods are explicitly called for execution whereas Static block gets executed when the Class gets loaded by the JVM.

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

   Like      Discuss      Correct / Improve     java   oops   static   static method   static block   difference between   similarity      basic        frequent

Try 1 Question(s) Test


 Q55. 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


Frequently asked to fresh graduates and less experienced.
 Q56. Difference between Compositions and Inheritance ?Core Java
Admin
info@buggybread.com
Ans. Inheritance means a object inheriting reusable properties of the base class. Compositions means that an abject holds other objects.

In Inheritance there is only one object in memory ( derived object ) whereas in Composition , parent object holds references of all composed objects.

From Design perspective - Inheritance is "is a" relationship among objects whereas Composition is "has a" relationship among objects.

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

   Like      Discuss      Correct / Improve     java   oops   oops concepts   inheritance   composition   difference between   basic interview question      basic        frequent

Try 2 Question(s) Test


 Q57. Difference between Static and Singleton Class ?Core Java2016-11-30 21:00:43

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

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

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

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

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

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

   Like      Discuss      Correct / Improve     Static Class  Singleton  Static Class vs Singleton     Netflix  EPAM  Ebay      Intermediate        frequent


 Q58. 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


 Q59. 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 ?

OpenXavaSPRING MVCApache StripesCheck everything
that is Best in Java

Click Here



Very Frequently asked.
 Q60. Explain throw, throws , try and catch in Java ?Core Java
Admin
info@buggybread.com
Ans. throw is used to re throw an exception.

throws is used to declare that the method throws the respective exceptions.

try block is used to identify if the respective block has thrown any exception.

catch is used to catch the exception that has been thrown by the respective try block.

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

   Like      Discuss      Correct / Improve     java   exception handling   throw   throws   try   catch     Vidram Solutions  Cognizant (CTS)      basic        frequent


Not frequently asked as it was introduced with Java 8.
 Q61. What is StringJoiner ?Core Java
Admin
info@buggybread.com
Ans. StringJoiner is a util method to construct a string with desired delimiter. This has been introduced with wef from Java 8.

Sample Code

StringJoiner strJoiner = new StringJoiner(".");
strJoiner.add("Buggy").add("Bread");
System.out.println(strJoiner); // prints Buggy.Bread


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

   Like      Discuss      Correct / Improve     java   java8   java 8   string   stringjoiner


Very Frequently asked. Have been asked in HCL Technologies very frequently ( based on 2 feedback ). Among first few questions in many interviews.
  Q62. 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 ).

 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  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)      basic        frequent


 Q63. Which of the following can be marked static ?

a. Methods , Variables and Initialization Blocks.
b. Methods , Variables , Initialization Blocks and Outer Classes and nested Classes.
c. Methods , Variables , Initialization Blocks and Outer Classes.
d. Methods , Variables , Initialization Blocks and nested Classes
Core Java
Anonymous
Ans. Methods , Variables , Initialization Blocks and nested Classes

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

   Like      Discuss      Correct / Improve     oops   java   static   nested classes   static nested classes

Try 2 Question(s) Test


 Q64. Which of the following collections stores its elements in insertion Order ?

a. HashMap
b. TreeMap
c. LinkedHashMap
d. LinkedMap
Core Java
Anonymous
Ans. LinkedHashMap

  Sample Code for LinkedHashMap

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

   Like      Discuss      Correct / Improve     linkedhashmap   collections   java   map


 Q65. In what order the elements of a HashSet are retrieved ?

a. Random Order
b. Insertion Order
c. Natural Sorting Order
d. Inverse Natural Sorting Order
Core Java
Anonymous
Ans. Random Order

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

   Like      Discuss      Correct / Improve     collections   set   hashset   java

Try 1 Question(s) Test


 Q66. Collections.sort can only be performed on ..

a. Set
b. List
c. Map
d. Any Collection implementation
Core Java
Anonymous
Ans. List

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

   Like      Discuss      Correct / Improve     collections   java   sorting

Try 2 Question(s) Test


 Q67. Which of the following is false about main method ?

a. It should be declared public and static
b. it should have only 1 argument of type String array
c. We can override main method
d. We can overload main method
Core Java
Anonymous
Ans. We can override main method

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

   Like      Discuss      Correct / Improve     java   main method


 Q68. Which of the following is false about Constructors ?

a. Constructor can be overloaded
b. A no argument constructor is provided by the compiler if we declare only constructors with arguments.
c. Constructors shouldn't have any return types , not even void.
d. If super is not explicitly called, still super() is intrinsically added by the compiler.
Core Java
Anonymous
Ans. A no argument constructor is provided by the compiler if we declare only constructors with arguments.

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

   Like      Discuss      Correct / Improve     java   oops   constructor

Try 2 Question(s) Test


 Q69. Which of the following doesn't extend Collection interface ?

a. Set
b. List
c. Map
d. Queue
Core Java
Anonymous
Ans. Map

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

   Like      Discuss      Correct / Improve     java   collections   collection interface



Do you think these are the Best Java Frameworks ?

OpenXavaSPRING MVCApache StripesCheck everything
that is Best in Java

Click Here



 Q70. 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


 Q71. Which of the following Java feature promotes access protection or Hiding ?

a. Inheritance
b. Encapsulation
c. Abstraction
d. Composition
Core Java
Anonymous
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


 Q72. enums are intrinsically ..

a. private
b. public
c. static
d. final
Core Java
Anonymous
Ans. static

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

   Like      Discuss      Correct / Improve     java   enum


 Q73. Difference between parameters and arguments ?Core Java
Admin
info@buggybread.com
Ans. Parameters are the variables that the method is expected to receive along with the method call. Arguments are the values which are passed on while calling the methods.

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

   Like      Discuss      Correct / Improve     parameter   argument  method   function  java      basic


 Q74. In which cases , moving methods to utility class could be useful ?Core Java

Ans. It could be worthy to move a method to util class if the method needs to be shared, doesn't require polymorphic behavior and need not be overridden in special cases.

Don't belong to one group through is-a relationship ( You can share through parent class method )

Don't implement a specific interface ( java 8 default methods )

Doesn't involve complex computing as you will be loosing the benefit of object state with just static method.

Doesn't require polymorphic behavior as static methods don't participate in runtime polymorphism.

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

   Like      Discuss      Correct / Improve     utility classes   util classes   static methods   application design        rare


 Q75. 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     BSL Information Technology  Data64


 Q76. What are constructors and Destructors in Java ?Core Java2016-06-03 10:09:28

Ans. Constructors are used for initializing the object state once it is initialized and memory has been reserved for it.

Destructor is used to de-allocate memory allocated by objects.

There are no destructors in Java. Alternatively, Java provides Automatic garbage collection i.e automatically releasing the un-referenced memory.


  Sample Code for constructor

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

   Like      Discuss      Correct / Improve     constructors  destructors     Quinnox  Tribro

Try 1 Question(s) Test


 Q77. What is the difference between the following two code lines ?

1. new OuterClass().new InnerClass();

2. new OuterClass.InnerClass();
Core Java2016-06-30 14:45:37

Ans. In first case we are trying to initialize Inner class object using the instance of Outer Class whereas in second case we are trying to initialize the Inner class object directly using the Outer class name.

In second case , Inner class is "static inner class" as we cannot access "non static inner class" using Classname alone.

In first case, the inner class could be either "static inner class" or "non static inner class".

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

   Like      Discuss      Correct / Improve     inner classes  inner class   static inner class   new operator


 Q78. Why HashTable has been deprecated ?Core Java2016-07-08 10:01:58

Ans. HashTable has been Deprecated as an alternative ConcurrentHashMap has been provided which 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 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


 Q79. What are the different uses of Interfaces in Java ?Core Java2016-07-20 15:14:43

Ans. 1. Regulation / Enforcement / Policy / Contract , It's primary use

2. Use as a collection of utility methods(since java 8 through default methods)

3. Collecting constants together, As Interface are lighter, it makes sense to use them instead of classes if no getters and setters required.

4. Creation of Custom Annotations

5. Special services like marker interface

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

   Like      Discuss      Correct / Improve     interfaces   uses of interfaces in java     BMC Software



Do you think these are the Best Java Frameworks ?

OpenXavaSPRING MVCApache StripesCheck everything
that is Best in Java

Click Here



Basic and Very Frequently asked.
  Q80. What is Polymorphism in Java ?Core Java2016-11-06 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  oops concepts     Credit Suisse  Unbounded Solutions  Microsoft   Google  Purch  HCL Technologies  Tata Consultancy (TCS)  Wipro  Mathworks  Accenture  ZonOff  ZapCom  Addteq  Priceline.com  Acute Informatics  Trimax IT Infrastructure & Services   USAA      Basic        frequent

Try 2 Question(s) Test


 Q81. Why two types of memory - stack and heap are required by Java ?Core Java2016-12-21 13:08:55

Ans. Because of the life cycle requirement for different type of values in java.

variables initialized and used in functions needs to be destructed with the execution of function and hence kept in stack. Same is applicable for the object references initialized within the method. If objects would have been created in stack, they wouldnt have been passed around across methods and hence they are created on heap.

So anything that is required beyond the scope of a method or function is kept on heap which is usually garbage collected by Java.

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

   Like      Discuss      Correct / Improve     memory management  heap  stack

Try 1 Question(s) Test


 Q82. What do you look for when you do code review ?Core Java2016-12-28 13:59:38

Ans. Modularity - First sign of good code is whether it has been segregated into methods and classes appropriately. I dont mind it in excess because I believe that is forward looking strategy as applications tends to expand and eventually become hard to read.

Self Explanatory - Variables and methods should be named in a way that the code should be self explanatory even without comments. Use of Constant variables to explain use of literal.

Proper Code Reuse - If there is anything being reused , it should be moved to parent classes / methods.

Proper composition calls - Composed hierarchy should not be access in just single line. One or two levels is ok but having multiple levels make it hard to read and debug.

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

   Like      Discuss      Correct / Improve     code review  clean code


 Q83. What are different types of variables a class can have ?Core Java2017-01-07 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


 Q84. Can we have multiple main methods in a single class ?Core Java2017-01-12 11:00:02

Ans. We can overload the main method by specifying different argument types. For example -

2 main methods with different arguments is perfectly legal

public static void main();
public static void main(String[] args);

The following are not legal as compiler will complain of duplicate methods

public static void main(String[] args);
public static void main(String[] args);

Even The following are not legal as we cannot overload on return types

public static String main(String[] args);
public static void main(String[] args);

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

   Like      Discuss      Correct / Improve     main method     HCL Technologies  SapientNitro


 Q85. Which elements of a class are ignored during serialization ?Core Java2017-01-12 11:08:21

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     HCL Technologies      intermediate        frequent

Try 1 Question(s) Test


 Q86. Can we declare static variables as transient ?Core Java2017-01-12 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


 Q87. Which of the following are valid declarations

1. void method(int... x){};
2. void method(int.. x){};
3. void method(int.. .x){};
4. void method(int ...x){};
5. void method(int... x){};
6. void method(int ... x){};
7. void method(int x, int... y){};
8. void method(int... x, int y){};
9. void method(int... x,int... y){};
Core Java2017-05-22 21:22:57

Ans. 1st is a valid and standard declaration.

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

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

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

7 is valid declaration.

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

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

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


 Q88. What is the difference between these two method declarations ?

private static void method(String[] arg)

and

private static void method(String... arg)
Core Java2017-05-23 08:41:54

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


  Q89. What are the different types of inner classes ?Core Java
Anonymous
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     Infosys  Tata Consultancy (TCS)  HCL Technologies  IBM  IBM India  Gateway Media      basic        frequent

Try 1 Question(s) Test



Do you think these are the Best Java Frameworks ?

OpenXavaSPRING MVCApache StripesCheck everything
that is Best in Java

Click Here



Very Frequently asked across all type of companies and across all levels.
  Q90. 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  Deegit  Cerner      basic        frequent

Try 1 Question(s) Test


 Q91. What are the Wrapper classes available for primitive types ?Core Java
Anonymous
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


 Q92. Does Constructor creates the object ?Core Java
Anonymous
Ans. New operator in Java creates objects. Constructor is the later step in object creation. Constructor's job is to initialize the members after the object has reserved memory for itself.

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

   Like      Discuss      Correct / Improve     java   constructor   object creation      intermediate        rare


  Q93. Does Java support Multiple Inheritance ?Core Java
Anonymous
Ans. Java doesn't support multiple inheritance. Interfaces does't facilitate inheritance and hence implementation of multiple interfaces doesn't make multiple inheritance.

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

   Like      Discuss      Correct / Improve     java   oop   oop concepts   inheritence   multiple inheritence   basic interview question     Credit Suisse  Sun Microsystems  VMware  NSEiT  Exterro  theScore  JP Morgan  Computrade Israel      basic        frequent

Try 1 Question(s) Test


Very frequently asked. Favorite question in Walk in Drive of many Indian service companies.
  Q94. 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  Forte Group  Mastercard      basic        frequent

Try 1 Question(s) Test


 Q95. 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


Very frequently asked. Favorite question in Walk in Drive of many Indian service companies.
  Q96. What is a final method ?Core Java
Anonymous
Ans. Its a method which cannot be overridden. Compiler throws an error if we try to override a method which has been declared final in the parent class.

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

   Like      Discuss      Correct / Improve     java   oops   final   final method     Oracle  Intertek  HCL Technologies  Tata Consultancy (TCS)  Accenture   IBM  Goldman Sachs   TrueCar   Intertek RedMane   Antra      basic        frequent

Try 1 Question(s) Test


 Q97. 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


 Q98. 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


 Q99. There are two objects a and b with same hashcode. I am inserting these two objects inside a hashmap.

hMap.put(a,a);
hMap.put(b,b);

where a.hashCode()==b.hashCode()

Now tell me how many objects will be there inside the hashmap?
Core Java
Anonymous
Ans. There can be two different elements with the same hashcode. When two elements have the same hashcode then Java uses the equals to further differentation. So there can be one or two objects depending on the content of the objects.

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

   Like      Discuss      Correct / Improve     java   hashcode   map   hashmap   object reference   advanced



Do you think these are the Best Java Frameworks ?

OpenXavaSPRING MVCApache StripesCheck everything
that is Best in Java

Click Here



Frequently asked to fresh graduates and less experienced developers.
 Q100. Explain multithreading in Java ?Core Java
Anonymous
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     Hamsini ECommerce   Cognizant (CTS)  Cumulus Systems  Cognizant (CTS)      intermediate        frequent

Try 1 Question(s) Test


next 100


Subscribe to Java News and Posts. Get latest updates and posts on Java from Buggybread.com
Enter your email address:
Delivered by FeedBurner



comments powered by Disqus
 

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

Any input from you will be highly appreciated and It will unlock the application for 10 more requests.

Company Name:
Questions Asked:
         

X Close this

X Close this

Help Us Improve.
Please share your
interview experience.

Company Name:   


Questions Asked: