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Java - Interview Questions and Answers - Order By Newest

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  Q41. Difference between Vector and ArrayList ?Core Java
Anonymous
Ans. Vectors are synchronized whereas Array lists are not.

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Frequently asked to fresh graduates.
  Q42. What is a Deadlock ?Operating System
Anonymous
Ans. When two threads are waiting each other and cant precede the program is said to be deadlock.

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Frequently asked to fresh graduates.
 Q43. Explain Thread States ?Operating System
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Ans. Runnable - waiting for its turn to be picked for execution by the thread schedular based on thread priorities.

Running - The processor is actively executing the thread code. It runs until it becomes blocked, or voluntarily gives up its turn.

Waiting: A thread is in a blocked state while it waits for some external processing such as file I/O to finish.

Sleeping - Java threads are forcibly put to sleep (suspended) with Thread.sleep. they can resume using Thread.resume method.

Blocked on I/O - Will move to runnable after I/O condition like reading bytes of data etc changes.

Blocked on synchronization - Will move to Runnable when a lock is acquired.

Dead - The thread is finished working.

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Very frequently asked.Usually among first few questions.
  Q44. What is MVC ? Design
Anonymous
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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 Q45. Similarity and Difference between static block and static method ?Core Java
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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.

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Very Frequently asked.
 Q46. Explain throw, throws , try and catch in Java ?Core Java
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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.

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 Q47. Difference between parameters and arguments ?Core Java
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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.

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  Q48. Difference between GET and POST Requests ?Web Service2016-07-22 15:00:21

Ans. GET is supposed to get information from the server. Client sends the minimal information so that Server can respond with the response body on basis of request. For example - You want to get complete employment record for employee id 123

POST is supposed to send the information for submission. Payload or a Body is usually sent so that it can be persisted on the server. For example - Sending the complete information of an employee ( id, name , dept etc ) to the server for persisting it.

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 Q49. Difference beween HashSet and TreeSet ?Core Java2016-11-27 19:08:35

Ans. 1. HashSet doesnt maintain its elements in any specific order and is all random whereas TreeSet maintains elements in natural order 9 order defined by the equals method of TreeSet element type )

2. TreeSet doesnt allow null elements whereas HashMap does.

3. As TreeSet orders elements and is hence insertion is comparatively slower.

4. HashSet performs basic operations like add(), remove(), contains(), size() etc. in a constant size time. A TreeSet performs these operations at the order of log(n) time.

5. HashMap in Java internally backs a HashSet. A NavigableMap backs a TreeSet internally.

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 Q50. If an Abstract class has only abstract methods, What's the difference between such a class and an interface ?Core Java2017-05-07 07:26:29

Ans. Such a class still can have member elements which can be inherited and hence facilitate code reuse. Moreover Abstract class can have non final static elements whereas interfaces are only allowed to have static final elements.

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 Q51. What is the difference between inner class and sub class ?Core Java2017-06-18 16:30:30

Ans. Inner Class is a class that is nested within another class whereas sub class is a class that extends or inherit another class.

Inner class can only be accessed using reference of outer class ( Class name , if inner class is static or object reference, if inner class is non static ) whereas Sub class is accessed directly.

In terms of memory, inner class is stored just like another class having it's own body whereas sub class carries the body of parent class as well as it's own fields in memory.

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  Q52. What is JSON ?Json
Anonymous
Ans. JSON is "JavaScript Object Notation", primarily used for client-server or server-server communication. Its a much lighter and readable alternative to XML. JSON is language independent and is easily parse-able in all programming languages.

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 Q53. What is an API ( Application Programming Interface ) ?
Anonymous
Ans. An API is a kind of technical contract which defines functionality that two parties must provide: a service provider (often called an implementation) and an application. an API simply defines services that a service provider (i.e., the implementation) makes available to applications.

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 Q54. What is URL?
Java EE
Anonymous
Ans. URL is Uniform Resource Locator which is representation of HTTP address.

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 Q55. What is HTTP ?Java EE
Anonymous
Ans. HTTP or Hypertext Transfer Protocol is internet protocol for tranmission of hypertext ( text with meta data ) over internet.

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 Q56. Which access specifier can be used with Class ?Core Java
Anonymous
Ans. For top level class we can only use "public" and "default". We can use private with inner class.

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 Q57. Different ways of implementing Threads in Java ?Core Java
Anonymous
Ans. Threads in Java can be implement either by Extending Thread class or implementing runnable interface.

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 Q58. What is a Final Method ?Core Java
Anonymous
Ans. A Method that cannot be overriden in the sub class.

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Very Frequently asked.Favorite question in Walk in drive for many Indian service companies.
 Q59. What is a Final Class ?
Anonymous
Ans. A Class that cannot be sub classed.

  Sample Code for final class

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Very frequently asked. Usually asked with questions related to String.
  Q60. What is an Immutable Object ?Core Java
Anonymous
Ans. Object that can't be changed after instantiation.

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Very Frequently asked. Usually asked along with String Class related questions.
  Q61. What is an immutable class ?Core Java
Anonymous
Ans. Class using which only immutable (objects that cannot be changed after initialization) objects can be created.

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 Q62. Name few Java Exceptions ?Core Java
Anonymous
Ans. IndexOutofBoundException ,
NoClassDefFoundException ,
OutOfMemoryException ,
IllegalArgumentException,
NullPointerException,
IllegalStateException

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Frequently asked to fresh graduates and less experienced.
 Q63. Which of the following is tightly bound ? Inheritance or Composition ?Core Java
Anonymous
Ans. Inheritance.

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 Q64. How can we make sure that a code segment gets executed even in case of uncatched exceptions ?
Anonymous
Ans. By putting it within finally.

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 Q65. What is "super" used for ?
Anonymous
Ans. Used to access members of the base class.

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 Q66. What is "this" keyword used for ?
Anonymous
Ans. Used to represent an instance of the class in which it appears.

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 Q67. Difference between boolean and Boolean ?Core Java
Anonymous
Ans. boolean is a primitive type whereas Boolean is a class.

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Frequently asked to fresh graduates.
  Q68. Difference between Process and Thread ?Operating System
Anonymous
Ans. Process is a program in execution whereas thread is a separate path of execution in a program.

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 Q69. Difference between Serialization and Deserialization ?Core Java
Anonymous
Ans. Serialization is the process of writing the state of an object to a byte stream. Deserialization is the process of restoring these objects.

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 Q70. Explain Autoboxing ?Core Java
Anonymous
Ans. Autoboxing is the automatic conversion that the Java compiler makes between the primitive types and their corresponding object wrapper classes

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