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Frequently asked question in companies using hibernate.
  Q31. Difference between first level and second level cache in hibernate ?Hibernate
Ans. 1. First level cache is enabled by default whereas Second level cache needs to be enabled explicitly.

2. First level Cache came with Hibernate 1.0 whereas Second level cache came with Hibernate 3.0.

3. First level Cache is Session specific whereas Second level cache is shared by sessions that is why First level cache is considered local and second level cache is considered global.

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   Like         Discuss         Correct / Improve     hibernate   orm   hibernate cache   architecture   technical lead   first level cache vs second level cache     Asked in 18 Companies      Intermediate        frequent

Very frequently asked. Favorite question in Walk in Drive of many Indian service companies.
  Q32. What is a final method ?Core Java
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.

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   Like         Discuss         Correct / Improve     java   oops   final   final method     Asked in 30 Companies      basic        frequent
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  Q33. 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

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

Frequently asked. Favorite question in Walk in Drive of many Indian service companies.
  Q34. What are the methods of Object Class ?Core Java
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.

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   Like         Discuss         Correct / Improve     java   oops   object class     Asked in 16 Companies      basic        frequent
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 Q35. 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
Ans. Synchronized

  Sample Code for Synchronized

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   Like         Discuss         Correct / Improve     java   threads   multithreading     Asked in 2 Companies      basic

Almost sure to be asked in every company using any Dependency Injection framework ( Spring, Guice etc )
  Q36. 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.

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  Q37. What is the use of Transient Keyword ?Core Java
Ans. It in Java is used to indicate that a field should not be serialized.

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Very frequently asked.Usually among first few questions.
  Q38. 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

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 Q39. 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 ");
}
}

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Frequently asked to fresh graduates.
 Q40. 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.

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   Like         Discuss         Correct / Improve     database  acid     Asked in 7 Companies      Intermediate
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Very frequently asked in companies using SOA.
  Q41. What are RESTful Web Services ?Rest
Ans. REST or Representational State Transfer is a flexible architecture style for creating web services that recommends the following guidelines -

1. http for client server communication,
2. XML / JSON as formatiing language ,
3. Simple URI as address for the services and,
4. stateless communication.

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   Like         Discuss         Correct / Improve     java   web services   rest   java   j2ee  architecture     Asked in 14 Companies      intermediate        frequent

Frequently asked. Among first few questions in the J2EE segment of interview.
  Q42. What is deployment descriptor ?

or

What is the use of deployment descriptor ?		Java EE
Ans. Deployment Descriptor which is usually web.xml is used to specify the classes, resources and configuration of the application and how the web server uses them to serve web requests.This file is usually added to WEB-INF folder and contains following

* Servlet entries and url mapping
* Plugins
* Some info regarding authentication / filters
* Landing Page
* Event Handlers

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   Like         Discuss         Correct / Improve     web.xml   servlets  deployment descriptor     Asked in 15 Companies      basic        frequent
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Frequently asked Generic Question.
  Q43. Why do you want to work for our company ?General
Ans. [Open Ended Answer]

Usually answered stating your keen interest in the role offered and challenges and opportunities the role offers.

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   Like         Discuss         Correct / Improve          Asked in 42 Companies        frequent

 Q44. 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.

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   Like         Discuss         Correct / Improve     static  transient  serialization     Asked in 1 Companies      expert        rare
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 Q45. Difference between JVM, JRE and JDK ?Core Java
Ans. JDK(Java Development kit) = Development Kit comprising of JVM , library and development tools for developers

JRE (Java Run time Environment) - Comprise of JVM and set of libraries

JVM(Java Virtual Machine) = Interpreter which reads the .class file line by line.

When we install JDK, JRE also get installed so we can write,compile and excute our code. Used by developer. Without JDK we can only execute the program using JRE.

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Very Frequently asked across all type of companies and across all levels.
  Q46. 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.

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 Q47. 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
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.

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Frequently asked question for intermediate developers. Frequently asked in HCL Technologies and EPAM.
  Q48. 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

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Advanced level question. Recently asked in few Indian service companies ( Based on 3 inputs )
 Q49. 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.

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  Q50. 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.

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Frequently asked to fresh graduates and less experienced.
  Q51. 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.

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  Q52. Can we overload main method in Java ?Core Java
Ans. Yes, but the overloaded main methods without single String[] argument doesn't get any special status by the JVM. They are just another methods that needs to be called explicitly.

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Frequently asked in high end product companies. Frequently asked in Deloitte.
  Q53. 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.

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 Q54. Can we have multiple main methods in a single class ?Core Java
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);

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   Like         Discuss         Correct / Improve     main method     Asked in 2 Companies

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.
  Q55. What is the difference between StringBuffer and String class ?Core Java
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.

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 Q56. How to implement an immutable class ?Core Java
Ans. We can make a class immutable by

1. Making all methods and variables as private.

2. Setting variables within constructor.

Public Class ImmutableClass{

private int member;
ImmutableClass(int var){
member=var;
}
}

and then we can initialize the object of the class as

ImmutableClass immutableObject = new ImmutableClass(5);

Now all members being private , you cant change the state of the object.

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Frequently asked to fresh graduates.
  Q57. What is a Deadlock ?Operating System
Ans. When two threads are waiting each other and cant precede the program is said to be deadlock.

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 Q58. What is a stream and what are the types of Streams and classes of the Streams?Core Java
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.

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 Q59. what is fail fast and Fail Safe in collections?Core Java
Ans. Iterators in java are used to iterate over the Collection objects.

Fail-Fast iterators immediately throw ConcurrentModificationException if there is any addition, removal or updation of any element.

Fail-Safe iterators don't throw any exception if a collection is structurally modified while iterating over it. This is because, they operate on the clone of the collection and not on the original collection.

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   Like         Discuss         Correct / Improve     ail fast   fail saf     Asked in 9 Companies      intermediate

 Q60. What is a ConcurrentHashMap ?Core Java
Ans. ConcurrentHashMap is a hashMap that allows concurrent modifications from multiple threads as there can be multiple locks on the same hashmap.

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