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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/
   




Interview Questions and Answers - Order By Newest

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 Q31. Example of Observer Design Pattern ?
Ans. Listeners.

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 Q32. Difference between Factory and Strategy Design Pattern ?Design
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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 Q33. Which kind of memory is used for storing object member variables and function local variables ?
Ans. Local variables are stored in stack whereas object variables are stored in heap.

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 Q34. Why do member variables have default values whereas local variables don't have any default value ?
Core Java
Ans. member variable are loaded into heap, so they are initialized with default values when an instance of a class is created. In case of local variables, they are stored in stack until they are being used.

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 Q35. Difference between static vs. dynamic class loading?Core Java
Ans. static loading - Classes are statically loaded with Java new operator.

dynamic class loading - Dynamic loading is a technique for programmatically invoking the functions of a class loader at run time.

Class.forName (Test className);

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 Q36. What is PermGen or Permanent Generation ?Core Java
Ans. The memory pool containing all the reflective data of the java virtual machine itself, such as class and method objects. With Java VMs that use class data sharing, this generation is divided into read-only and read-write areas. The Permanent generation contains metadata required by the JVM to describe the classes and methods used in the application. The permanent generation is populated by the JVM at runtime based on classes in use by the application. In addition, Java SE library classes and methods may be stored here.

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 Q37. What is metaspace ?Core Java
Ans. The Permanent Generation (PermGen) space has completely been removed and is kind of replaced by a new space called Metaspace. The consequences of the PermGen removal is that obviously the PermSize and MaxPermSize JVM arguments are ignored and you will never get a java.lang.OutOfMemoryError: PermGen error.

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 Q38. Why String is popular HashMap key in Java?Core Java
Ans. Since String is immutable, its hashcode is cached at the time of creation and it doesnt need to be calculated again. This makes it a great candidate for key in a Map and its processing is fast than other HashMap key objects. This is why String is mostly used Object as HashMap keys.

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 Q39. What does String intern() method do?Core Java
Ans. intern() method keeps the string in an internal cache that is usually not garbage collected.

Moreover provide reference for scp object for corresponding string object present in heap memory.

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 Q40. How substring() method of String class create memory leaks?Core Java
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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  Q41. What are Default Methods ?Core Java
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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 Q42. What are design situations to use Singleton and Prototype Design Pattern ?Design
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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 Q43. How Marker interfaces works internally ?Core Java
 This question was recently asked at 'GGK Technologies'.This question is still unanswered. Can you please provide an answer.


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 Q44. Why do we need to specify import statement ? Don't you think Java could have been designed in such a way to automatically import everything that's in the class path ?Core Java
Ans. Java could design it in such a manner but would result in ambiguity if there are multiple files with the same name. The only way to get over it to show the message when you use any such class to provide explicit import with the package prefix. The other problem could be that Java might have to change the early import to Late import and check what's being used to decide what needs to be imported as otherwise you will see errors regarding the ambiguous imports with duplicate file name.

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 Q45. Does use of Final class enforces composition over Inheritance in Java ? Core Java
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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 Q46. What could be the reasons for restricting inheritance using final class ?Core Java
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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 Q47. What will happen if there are no interfaces in Java ?Core Java
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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 Q48. Difference between long.Class and Long.TYPE ?
Ans. They both represent the long primitive type. They are exactly the same.

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 Q49. Which memory segment loads the java code ?Core Java
Ans. Code segment.

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 Q50. Can a lock be acquired on a class ?
Ans. Yes, a lock can be acquired on a class. This lock is acquired on the class's Class object.

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 Q51. Shall we use abstract classes or Interfaces in Policy / Strategy Design Pattern ?
Ans. Strategy deals only with decision making at runtime so Interfaces should be used.

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 Q52. Will Compiler creates a default no argument constructor if we specify only multi argument constructor ?
Ans. No, Compiler will create default constructor only if we don't specify any constructor.

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 Q53. What is ThreadFactory ?Core Java
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.
  Q54. What are new features introduced with Java 8 ?Core Java
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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 Q55. How is HashSet maintained in memory by Java ?Core Java
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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 Q56. What are the advantages and disadvantages of CopyOnWriteArrayList ?Core Java
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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 Q57. Which UML diagrams you usually use for design ?Design
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 )
 Q58. What are the technologies used in Jira ?Tools
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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 Q59. Which sorting algorithm is used by Collections.sort() in Java ?Core Java
Ans. The sorting algorithm is a modified mergesort. This algorithm offers guaranteed n log(n) performance.

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 Q60. Which tree is used to implement TreeMap in Java?
Ans. Red Black Tree

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