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Expert Websoft Java Coaching Institute

Mayuri apts,Prashant Society,lane no. 3, plot no.21, behind Krishna Hospital, Paud Rd, Kothrud, Pune, Maharashtra 411038, India

Link: http://expertwebsoft.com/
   




Java - Interview Questions and Answers - Order By Newest

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 Q31. How substring() method of String class create memory leaks?Core Java
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Ans. substring method would build a new String object keeping a reference to the whole char array, to avoid copying it. Hence you can inadvertently keep a reference to a very big character array with just a one character string.

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  Q32. What are Default Methods ?Core Java
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Ans. With Java 8, We can provide method definitions in the Interfaces that gets carried down the classes implementing that interface in case they are not overridden by the Class. Keyword "default" is used to mark the default method.

  Sample Code for interface default

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Frequently asked in high end product companies. Frequently asked in Deloitte.
  Q33. How is Hashmap internally implemented in Java ?Core Java2016-12-06 08:49:37

Ans. https://www.quora.com/How-is-Hashmap-in-Java-implemented-internally-What-are-the-pros-and-cons-to-use-it-What-are-the-complexities-it-provides-for-insert-delete-and-lookup/answer/Anshudeep-Bajpai?srid=iwnK

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 Q34. Does use of Final class enforces composition over Inheritance in Java ? Core Java2018-07-16 06:49:53

Ans. Yes, to a certain extent. But the objective for Final class could be beyond just enforcing composition as certain classes might have been created without inheritance or composition in mind.

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 Q35. What could be the reasons for restricting inheritance using final class ?Core Java2018-07-16 06:52:00

Ans. 1. Enforcing composition over inheritance
2. Restricting overriding of certain methods
3. Final methods are faster than regular instance methods
4. Enforcing Immutability

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 Q36. What will happen if there are no interfaces in Java ?Core Java2018-12-11 16:16:37

Ans. Abstract classes can take care of that to a certain extent. Though they are little heavier than Interfaces but An abstract class with all abstract methods and no instance variables will be able to help with everything that currently an interface does.

The only problem is that a class can only extend one class whereas it can implements multiple interfaces and that is the reason Interfaces were introduced in Java, i.e to get over the problem of multiple inheritance.

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 Q37. Difference between long.Class and Long.TYPE ?
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Ans. They both represent the long primitive type. They are exactly the same.

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 Q38. Which memory segment loads the java code ?Core Java
Anonymous
Ans. Code segment.

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 Q39. Can a lock be acquired on a class ?
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Ans. Yes, a lock can be acquired on a class. This lock is acquired on the class's Class object.

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 Q40. Difference between Factory and Builder Design Pattern ?Design
Anonymous
Ans. Builder pattern is the extension of Factory pattern wherein the Builder class builds a complex object in multiple steps.

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 Q41. Difference between Proxy and Adapter ?Design
Anonymous
Ans. Adapter object has a different input than the real subject whereas Proxy object has the same input as the real subject. Proxy object is such that it should be placed as it is in place of the real subject.

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 Q42. Difference between Adapter and Facade ?Design
Anonymous
Ans. The Difference between these patterns in only the intent. Adapter is used because the objects in current form cannot communicate where as in Facade , though the objects can communicate , A Facade object is placed between the client and subject to simplify the interface.

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 Q43. Example of Chain of Responsibility Design Pattern ?
Anonymous
Ans. Exception Handling Throw mechanism.

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 Q44. Example of Observer Design Pattern ?
Anonymous
Ans. Listeners.

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 Q45. Difference between Factory and Strategy Design Pattern ?Design
Anonymous
Ans. Factory is a creational design pattern whereas Strategy is behavioral design pattern. Factory revolves around the creation of object at runtime whereas Strategy or Policy revolves around the decision at runtime.

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 Q46. Shall we use abstract classes or Interfaces in Policy / Strategy Design Pattern ?
Anonymous
Ans. Strategy deals only with decision making at runtime so Interfaces should be used.

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 Q47. Which kind of memory is used for storing object member variables and function local variables ?
Anonymous
Ans. Local variables are stored in stack whereas object variables are stored in heap.

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 Q48. Will Compiler creates a default no argument constructor if we specify only multi argument constructor ?
Anonymous
Ans. No, Compiler will create default constructor only if we don't specify any constructor.

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 Q49. What is ThreadFactory ?Core Java
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Ans. ThreadFactory is an interface that is meant for creating threads instead of explicitly creating threads by calling new Thread(). Its an object that creates new threads on demand. Using thread factories removes hardwiring of calls to new Thread, enabling applications to use special thread subclasses, priorities, etc.

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Frequently asked these days as there are major changes in Java 8.
  Q50. What are new features introduced with Java 8 ?Core Java
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Ans. Lambda Expressions , Interface Default and Static Methods , Method Reference , Parameters Name , Optional , Streams, Concurrency.

  Sample Code for Lambda

  Sample Code for interface default

  Sample Code for Optional

  Sample Code for Streams

  Sample Code for java.time

  Sample Code for Predicate

  Sample Code for Consumer

  Sample Code for MapMerge

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 Q51. How is HashSet maintained in memory by Java ?Core Java
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Ans. HashSet is maintained as HashMap by Java with values of the HashSet as Keys of the HashMap and value of the HashMap as the constant PRESENT.

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 Q52. What are the advantages and disadvantages of CopyOnWriteArrayList ?Core Java
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Ans. This collections class has been implemented in such a manner that it can never throw ConcurrentModificationException. As it performs update and write operations by creating a new copy of ArrayList, It's slower compared to ArrayList.

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 Q53. Which UML diagrams you usually use for design ?Design
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Ans. Use Case Diagram, Component Diagram for High level Design and Class Diagram , Sequence Diagram for low level design.

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Frequently asked in Tata Consultancy (TCS) interview ( Based on 2 Feedback )
 Q54. What are the technologies used in Jira ?Tools
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Ans. JIRA is written in Java and uses the Pico IOC container,Apache OFBiz entity engine, and WebWork technology stack. For remote procedure calls (RPC), JIRA supports REST, SOAP, and XML RPC.

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 Q55. Which sorting algorithm is used by Collections.sort() in Java ?Core Java
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Ans. The sorting algorithm is a modified mergesort. This algorithm offers guaranteed n log(n) performance.

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 Q56. Which tree is used to implement TreeMap in Java?
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Ans. Red Black Tree

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 Q57. What are design situations to use Singleton and Prototype Design Pattern ?Design2016-07-28 20:28:43

Ans. Both are creational design patterns.

Singleton is used when we would like to reuse an object if object is not supposed to hold request or thread specific information. Inversely Prototype is used in situations where we would like to reuse the object information but the request / thread may require it own data to be persisted.

In short, Singleton is used in situations where we can live with single object being shared across multiple requests or threads whereas Prototype is used when we need duplicate copies of objects.

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 Q58. How can we catch an exception thrown by another thread ?Core Java2016-11-17 11:38:29

Ans. http://stackoverflow.com/a/6548203/2789764

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 Q59. Design a Data Structure for a full text Search ?Design2016-12-13 14:47:02

 This question was recently asked at 'Myntra'.This question is still unanswered. Can you please provide an answer.


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   Like         Discuss         Correct / Improve     Full Text Search  Data Structure     Asked in 1 Companies      expert


 Q60. What is serialVersionUID ?Core Java2016-12-20 17:26:52

Ans. Everytime an object is serialized the java serialization mechanism automatically computes a hash value by passing the meta information for the class. This id is used during deserialization to verify that the sender and receiver of a serialized object have loaded classes for that object that are compatible with respect to serialization

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