Search Interview Questions

Ans. Polymorphism means the condition of occurring in several different forms.

Polymorphism in Java is achieved in two manners

1. Static polymorphism is the polymorphic resolution identified at compile time and is achieved through function overloading whereas

2. Dynamic polymorphism is the polymorphic resolution identified at runtime and is achieved through method overriding.

Sample Code for overloading

Sample Code for overriding

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

_{Like Discuss Correct / Improve polymorphism object oriented programming (oops) oops concepts oops concepts Asked in 108 Companies Basic frequent}

Q32. What are the benefits of Enums ?

Ans. Enums in Java are used to declare predefined objects and then reuse them. they offer many benefits

1. Enum instance are type safe and thread safe.

2. Enum instances are singleton and hence reused.

3. If we use Enums with Switch , It makes sure that the passed argument is either of its instance and hence provides a safeguard.

4. If we use Enum with Sorted Collections we can sort the elements with a predefined priorities ( as per constant declaration in enum )

5. We can use Enum as a Factory by defining its constructor.

6. We can store related constant data within enum. For example - If we know the values for the map upfront, we can alternatively use an enum.

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

_{Like Discuss Correct / Improve Asked in 6 Companies}

Q33. What is a self Join and give an example of a self Join ?

or

What is self Join and What is it's purpose ?

Database

Ans. When a Table Join itself , it's a Self Join. For example - we like to know the pair of department names where first dept has lesser employees than the later.

Select D1.name , D2.name from Dept D1, Dept D2 where D1.employee_count < D2.employee_count

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

_{Like Discuss Correct / Improve sql joins self join self-join Pair of employee names with first having lesser salary than later Pair of department names where first dept has lesser employees than the later Asked in 26 Companies basic frequent}

Q34. What is a cookie ?

Java EE

Ans. A cookie is a small piece of text stored on a user's computer by the browser for a specific domain. Commonly used for authentication, storing site preferences, and server session identification.

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

_{Like Discuss Correct / Improve cookie javascript web application session management browser j2ee Asked in 16 Companies basic frequent}

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

Q35. Difference between TreeMap and HashMap ?

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 treemap vs hashmap Asked in 31 Companies basic frequent}

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

Q36. Difference between Public, Private, Default and Protected ?

Ans. Private - Not accessible outside object scope.

Public - Accessible from anywhere.

Default - Accessible from anywhere within same package.

Protected - Accessible from object and the sub class objects.

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

_{Like Discuss Correct / Improve java oop access specifier public private default protected public vs private vs default vs protected Asked in 12 Companies basic frequent}

Frequently asked at HCL Technologies ( Based on 3 feedback )

Q37. Difference between Checked and Unchecked exceptions ?

Ans. Checked exceptions are the exceptions for which compiler throws an errors if they are not checked whereas unchecked exceptions are caught during run time only and hence can't be checked.

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

_{Like Discuss Correct / Improve java exceptions checked exceptions unchecked exceptions exception handling checked vs unchecked exceptions Asked in 39 Companies basic frequent}

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

Q38. What is a Final Variable ?

Ans. Final variable is a variable constant that cannot be changed after initialization.

Sample Code for final variable

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

_{Like Discuss Correct / Improve oops java final final variable basic interview question Asked in 12 Companies basic frequent}

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

Q39. What is a final method ?

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 Asked in 30 Companies basic frequent}

Frequently asked.

Q40. What is an Iterator?

Ans. Iterator is an interface that provides methods to iterate over any Collection.

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

_{Like Discuss Correct / Improve java collections iterator Asked in 11 Companies basic frequent}

Very frequently asked across all types of companies.

Q41. Difference between HashMap and Hashtable?

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 hashmap vs hashtable Asked in 14 Companies basic frequent}

Q42. What are transient variables in java?

Ans. Transient variables are variable that cannot be serialized.

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

_{Like Discuss Correct / Improve java serialization transient Asked in 15 Companies intermediate rare}

Q43. What is casting?

Ans. There are two types of casting, casting between primitive numeric types and casting between object references. Casting between numeric types is used to convert larger values, such as double values, to smaller values, such as byte values. Casting between object references is used to refer to an object by a compatible class, interface, or array type reference

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

_{Like Discuss Correct / Improve java data types casting type casting basic interview question Asked in 8 Companies basic frequent}

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

Q44. Difference between Overloading and Overriding ?

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 overloading vs overriding Asked in 86 Companies basic frequent}

Q45. Difference between Vector and ArrayList ?

Ans. Vectors are synchronized whereas Array lists are not.

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

_{Like Discuss Correct / Improve java basic interview question vector arraylist collections synchronization vector vs arraylist Asked in 35 Companies basic frequent}

Q46. What is the use of Transient Keyword ?

Ans. It in Java is used to indicate that a field should not be serialized.

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

_{Like Discuss Correct / Improve java oops serialization transient java keywords Asked in 39 Companies intermediate frequent}

Very Frequently asked. Usually asked along with String Class related questions.

Q47. What is an immutable class ?

Ans. Class using which only immutable (objects that cannot be changed after initialization) objects can be created.

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

_{Like Discuss Correct / Improve java oops immutable immutability immutable immutability class string class basic interview question Asked in 18 Companies Basic frequent}

Very frequently asked in phone and walk in interviews.

Q48. What are Marker Interfaces ? Name few Java marker interfaces ?

Ans. An interface without any method declaration is called as marker interface. there are 3 in-built interfaces in JVM i.e. serializable, clonable, remote

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 Asked in 21 Companies intermediate frequent}

Very frequently asked. Usually difference between String,StringBuffer and StringBuilder is asked in different variations.

Q49. Difference between StringBuffer and StringBuilder ?

Ans. StringBuffer is synchronized whereas StringBuilder is not.

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

_{Like Discuss Correct / Improve java string stringbuffer string class stringbuilder synchronized basic interview question infosys technologies Asked in 17 Companies basic frequent}

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

Q50. Explain the scenerios to choose between String , StringBuilder and StringBuffer ?

or

What is the difference between String , StringBuilder and StringBuffer ?

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 String vs StringBuffer String vs StringBuilder String vs StringBuilder vs StringBuffer StringBuffer vs stringBuilder Asked in 29 Companies basic frequent}

Try 3 Question(s) Test

Q51. Is it necessary that each try block to be followed by catch block ?

Ans. It should be followed by either catch or finally block.

Sample Code for Retry in case of exception

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

_{Like Discuss Correct / Improve java exceptions exception handling try catch finally Oracle OCA Test Asked in 3 Companies basic frequent}

Q52. What is reflection ?

Ans. It is the process of examining / modifying the behaviour of an object at runtime.

Sample Code for reflection

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

_{Like Discuss Correct / Improve java reflection reflection api ebay mindtree Asked in 29 Companies basic frequent}

Advanced level question. Recently asked in few Indian service companies ( Based on 3 inputs )

Q53. What are various types of Class loaders used by JVM ?

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 Asked in 7 Companies}

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

Q54. What is the difference between final, finally and finalize() ?

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 final vs finally vs finalize Asked in 61 Companies basic frequent}

Try 4 Question(s) Test

Frequently asked in CTS ( Based on 2 feedback )

Q55. What is the difference between comparable and comparator in java.util pkg?

Ans. Comparable interface is used for single sequence sorting i.e.sorting the objects based on single data member where as comparator interface is used to sort the object based on multiple data members.

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

_{Like Discuss Correct / Improve java java.util comparable comparator collections Asked in 23 Companies basic frequent}

Recently asked in TCS , Tech Mahindra, HCL , Accenture and Fidelity.

Q56. Explain Flow of Spring MVC ?

Spring

Ans. The DispatcherServlet configured in web.xml file receives the request.

The DispatcherServlet finds the appropriate Controller with the help of HandlerMapping and then invokes associated Controller.

Then the Controller executes the logic business logic and then returns ModeAndView object to the DispatcherServlet.

The DispatcherServlet determines the view from the ModelAndView object.

Then the DispatcherServlet passes the model object to the View.

The View is rendered and the Dispatcher Servlet sends the output to the Servlet container.

Finally Servlet Container sends the result back to the user.

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

_{Like Discuss Correct / Improve j2ee spring mvc frameworks web applications architecture Asked in 11 Companies Basic frequent}

Very frequently asked.Usually among first few questions.

Q57. What is MVC ?

Design

Ans. MVC is a Design Pattern that facilititates loose coupling by segregating responsibilities in a Web application

1. Controller receives the requests and handles overall control of the request
2. Model holds majority of the Business logic, and
3. View comprise of the view objects and GUI component

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

_{Like Discuss Correct / Improve j2ee mvc mvc design pattern design pattern struts spring web application web frameworks ebay Asked in 60 Companies basic frequent}

Q58. Advantage of Collection classes over Arrays ?

Ans. Collections are re-sizable in nature. We can increase or decrease the size as per recruitment.
Collections can hold both homogeneous and heterogeneous data's.
Every collection follows some standard data structures.
Collection provides many useful built in methods for traversing,sorting and search.

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

_{Like Discuss Correct / Improve java collections collections classes advantages of collections over arrays collections vs arrays basic interview question Asked in 6 Companies basic frequent}

Q59. What is the use of HashCode in objects ?

Ans. Hashcode is used for bucketing in Hash implementations like HashMap, HashTable, HashSet etc.

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

_{Like Discuss Correct / Improve java string hashcode hash code string comparison hashtable Asked in 17 Companies basic frequent}

Q60. What do you mean by "Java is a statically typed language" ?