Interview Questions and Answers for 'Io' | Search Interview Question - javasearch.buggybread.com
Javasearch.buggybread.com

Search Interview Questions


 More than 3000 questions in repository.
 There are more than 900 unanswered questions.
Click here and help us by providing the answer.
 Have a video suggestion.
Click Correct / Improve and please let us know.
Label / Company      Label / Company / Text

   



Interview Questions and Answers - Order By Newest

   next 30
  Q31. What is casting?Core Java
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

 Q32. Can we use both "this()" and "super()" in a constructor ?Core Java
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     Asked in 1 Companies      intermediate        rare
Try 2 Question(s) Test

Very frequently asked. Favorite question in Walk in Drive of many Indian service companies.
  Q33. Difference between TreeMap and HashMap ?Core Java
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
Try 1 Question(s) Test

 Q34. What are concepts introduced with Java 5 ?Core Java
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

 Q35. Describe what happens when an object is created in Java ?Core Java
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

 Q36. What is session tracking and how do you track a user session in servlets?Java EE
Ans. Session tracking is a mechanism that servlets use to maintain state about a series requests from the same user across some period of time. The methods used for session tracking are:

User Authentication - occurs when a web server restricts access to some of its resources to only those clients that log in using a recognized username and password

Hidden form fields - fields are added to an HTML form that are not displayed in the client's browser. When the form containing the fields is submitted, the fields are sent back to the server

URL rewriting - every URL that the user clicks on is dynamically modified or rewritten to include extra information. The extra information can be in the form of extra path information, added parameters or some custom, server-specific URL change.

Cookies - a bit of information that is sent by a web server to a browser and which can later be read back from that browser.

HttpSession- places a limit on the number of sessions that can exist in memory.

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

   Like         Discuss         Correct / Improve     j2ee   servlets   session   session management   web applications   cookies   httpsession   url rewriting   architecture     Asked in 1 Companies

Advanced level question usually asked to senior developers , leads and architects.
 Q37. How does volatile affect code optimization by compiler?Core Java
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     Asked in 3 Companies      expert

 Q38. How to find whether a given integer is odd or even without use of modulus operator in java?Core Java
Ans. public static void main(String ar[])
{
int n=5;
if((n/2)*2==n)
{
System.out.println("Even Number ");
}
else
{
System.out.println("Odd Number ");
}
}

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

   Like         Discuss         Correct / Improve     java   code   coding   tricky questions   interesting questions   modulus operator     Asked in 4 Companies        frequent

Advanced level question frequently asked in US based companies. Recently asked in EMC and Intuit.
  Q39. Can you provide some implementation of a Dictionary having large number of words ? Solution
Ans. Simplest implementation we can have is a List wherein we can place ordered words and hence can perform Binary Search.

Other implementation with better search performance is to use HashMap with key as first character of the word and value as a LinkedList.

Further level up, we can have linked Hashmaps like ,

hashmap {
a ( key ) -> hashmap (key-aa , value (hashmap(key-aaa,value)
b ( key ) -> hashmap (key-ba , value (hashmap(key-baa,value)
....................................................................................
z( key ) -> hashmap (key-za , value (hashmap(key-zaa,value)
}

upto n levels ( where n is the average size of the word in dictionary.

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

   Like         Discuss         Correct / Improve     java   collections   hashmap   binary search   search algorithm   advanced   architecture   data structure     Asked in 6 Companies        frequent
Try 1 Question(s) Test

Frequently asked to fresh graduates and less experienced.
 Q40. Why do we write public static void main ? Can we use some other syntax too for main ?Core Java
Ans. 1. public is the access modifier that makes the method accessible from anywhere, static is the keyword that makes it accessible even without creating any object, void means it doesn't return anything , String args[] is the array of argument that the method receives.

2. If we use main without the string args , it will compile correctly as Java will treat it as just another method. It wont be the method "main" which Java looks for when it looks to execute the class and hence will throw

Error: Main method not found in class , please define the main method as:
public static void main(String[] args)

3. Main is not a keyword but a special string that Java looks for while initiating the main thread.

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

   Like         Discuss         Correct / Improve     java   main method     Asked in 4 Companies      basic        frequent
Try 1 Question(s) Test

Frequently asked to fresh graduates.
 Q41. What is ACID ?Database
Ans. ACID stands for Atomicity, Consistency, Isolation, Durability is a set of properties of database transactions.

Atomicity means all or nothing. i.e parts of a transaction shouldn't commit if any one of them fails. Either the whole transaction should succeed or it should be complete rollback.

Consistency means that any transaction should lead database from one stabe state to another.

Isolation means that the execution of transaction results in a system state that would be obtained if transactions were executed serially.

Durability means that when a transaction is committed it forms the permanent state of database.

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

   Like         Discuss         Correct / Improve     database  acid     Asked in 7 Companies      Intermediate
Try 1 Question(s) Test

 Q42. Can constructors be synchronized in Java ?Core Java
Ans. No. Java doesn't allow multi thread access to object constructors so synchronization is not even needed.

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

   Like         Discuss         Correct / Improve     synchronization   synchronize   constructor   java   multithreading   yes-no   advanced     Asked in 1 Companies      expert        rare

 Q43. What are the benefits of using Spring Framework ?Spring
Ans. Spring enables developers to develop enterprise-class applications using POJOs. The benefit of using only POJOs is that you do not need an EJB container product.

Spring is organized in a modular fashion. Even though the number of packages and classes are substantial, you have to worry only about ones you need and ignore the rest.

Spring does not reinvent the wheel instead, it truly makes use of some of the existing technologies like several ORM frameworks, logging frameworks, JEE, Quartz and JDK timers, other view technologies.

Testing an application written with Spring is simple because environment-dependent code is moved into this framework. Furthermore, by using JavaBean-style POJOs, it becomes easier to use dependency injection for injecting test data.

Spring is web framework is a well-designed web MVC framework, which provides a great alternative to web frameworks such as Struts or other over engineered or less popular web frameworks.

Spring provides a convenient API to translate technology-specific exceptions (thrown by JDBC, Hibernate, or JDO, for example) into consistent, unchecked exceptions.

Lightweight IoC containers tend to be lightweight, especially when compared to EJB containers, for example. This is beneficial for developing and deploying applications on computers with limited memory and CPU resources.

Spring provides a consistent transaction management interface that can scale down to a local transaction

  Sample Code for spring

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

   Like         Discuss         Correct / Improve     java   spring framework   mvc   spring container   architecture   technical architect   java architect   technical lead  ioc     Asked in 2 Companies      basic        frequent

Almost sure to be asked in every company using any Dependency Injection framework ( Spring, Guice etc )
  Q44. What is Dependency Injection or IOC ( Inversion of Control ) ?Design
Ans. It is a Design Pattern that facilitates loose coupling by sending the dependency information ( object references of dependent object ) while building the state of the object. Objects are designed in a manner where they receive instances of the objects from other pieces of code, instead of constructing them internally and hence provide better flexibility.

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

   Like         Discuss         Correct / Improve     design patterns   ioc ( Inversion of Control )  dependency injection     Asked in 83 Companies      intermediate        frequent

 Q45. Can we declare static variables as transient ?Core Java
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     Asked in 1 Companies      expert        rare
Try 1 Question(s) Test

 Q46. 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 Java
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

Very Frequently asked across all type of companies and across all levels.
  Q47. Difference between Public, Private, Default and Protected ?Core Java
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
Try 1 Question(s) Test

 Q48. Does Constructor creates the object ?Core Java
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

Frequently asked question for intermediate developers. Frequently asked in HCL Technologies and EPAM.
  Q49. What is Volatile keyword used for ?Core Java
Ans. Volatile is a declaration that a variable can be accessed by multiple threads and hence shouldnt be cached.

  Sample Code for volatile

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

   Like         Discuss         Correct / Improve     java   oops   synchronization   volatile   java keywords     Asked in 42 Companies      intermediate        frequent
Try 1 Question(s) Test

  Q50. What is the use of Transient Keyword ?Core Java
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
Try 2 Question(s) Test

 Q51. Will this code give error if i try to add two heterogeneous elements in the arraylist. ? and Why ?

List list1 = new ArrayList<>();
list1.add(5);
list1.add("5");
Ans. If we don't declare the list to be of specific type, it treats it as list of objects.

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

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

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

Advanced level question. Recently asked in few Indian service companies ( Based on 3 inputs )
 Q52. What are various types of Class loaders used by JVM ?Core Java
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

  Q53. Difference between SAX and DOM Parser ?Xml
Ans. A DOM (Document Object Model) parser creates a tree structure in memory from an input document whereas A SAX (Simple API for XML) parser does not create any internal structure.

A SAX parser serves the client application always only with pieces of the document at any given time whereas A DOM parser always serves the client application with the entire document no matter how much is actually needed by the client.

A SAX parser, however, is much more space efficient in case of a big input document whereas DOM parser is rich in functionality.

Use a DOM Parser if you need to refer to different document areas before giving back the information. Use SAX is you just need unrelated nuclear information from different areas.

Xerces, Crimson are SAX Parsers whereas XercesDOM, SunDOM, OracleDOM are DOM parsers.

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

   Like         Discuss         Correct / Improve     java   xml   parsers   sax   dom parser   difference   architecture   technical lead   technical architect  markup language   sax vs dom     Asked in 14 Companies        frequent
Try 1 Question(s) Test

Very frequently asked.Usually among first few questions.
  Q54. 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
Try 1 Question(s) Test

 Q55. How compiler handles the exceptions in overriding ?Core Java
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  object oriented programming (oops)  oops concepts   oops

 Q56. What things should be kept in mind while creating your own exceptions in Java?Core Java
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.
  Q57. Difference between Composition and Inheritance ?Core Java
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  object oriented programming (oops)  oops concepts   composition  object oriented programming (oops)  oops concepts   difference between   basic interview question     Asked in 12 Companies      basic        frequent
Try 2 Question(s) Test

 Q58. What will be the output of following code ?

public static void main(String[] args){
String name = null;
File file = new File("/folder", name);
System.out.print(file.exists());
}		Core Java
Ans. NullPointerException

at line: "File file = new File("/folder", name);"

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

   Like         Discuss         Correct / Improve     java   io   file   fileio   coding   code   file handling

 Q59. Which annotations are used in Hibernate ?Hibernate
Ans. @Entity
@Table
@Id
@Column
@Temporal
@Basic
@Enumerated
@Access
@Embeddable
@Lob
@AttributeOverride
@Embedded
@GeneratedValue
@ElementCollection
@JoinTable
@JoinColumn
@CollectionId
@GenericGenerator
@OneToOne
@OneToMany
@ManyToOne
@ManyToMany
@NotFound

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

   Like         Discuss         Correct / Improve     hibernate   annotations

Frequently asked in high end product companies. Frequently asked in Deloitte.
  Q60. How is Hashmap internally implemented in Java ?Core Java
Ans. https://medium.com/javarevisited/internal-working-of-hashmap-in-java-97aeac3c7beb#:~:text=HashMap%20internally%20uses%20HashTable%20implementation,the%20entries%20into%20the%20map.

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

   Like         Discuss         Correct / Improve     hashmap  collections  hashmap internal implementation     Asked in 20 Companies      expert        frequent

previous 30   next 30

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: