Interview Questions and Answers for 'Object' | Search Java 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

   



Java - Interview Questions and Answers - Order By Newest

   next 30
  Q31. Why java doesn't support multiple Inheritance ?

or

Explain Java Diamond Problem.
Core Java2017-01-09 11:45:34

Ans. class A {
void test() {
System.out.println("test() method");
}
}

class B {
void test() {
System.out.println("test() method");
}
}

Suppose if Java allows multiple inheritance like this,

class C extends A, B {
}

A and B test() methods are inheriting to C class.

So which test() method C class will take? As A & B class test() methods are different , So here we would Facing Ambiguity.

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

   Like         Discuss         Correct / Improve     multiple inheritance  object oriented programming (oops)  oops concepts  diamond problem     Asked in 20 Companies      basic        frequent


 Q32. Can we have multiple inheritance in java using abstract class ?Core Java2018-07-04 16:17:49

Ans. No

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

   Like         Discuss         Correct / Improve     abstract class   multiple inheritance  object oriented programming (oops)  oops concepts     Asked in 2 Companies


 Q33. 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.

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

   Like         Discuss         Correct / Improve     final class   composition  object oriented programming (oops)  oops concepts  inheritance  object oriented programming (oops)  oops concepts  composition  object oriented programming (oops)  oops concepts vs inheritance  object oriented programming (oops)  oops concepts      expert


 Q34. 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

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

   Like         Discuss         Correct / Improve     final class   reasons for final class   restricting inheritance  object oriented programming (oops)  oops concepts      expert


 Q35. Difference between Class#getInstance() and new operator ?
Admin
info@buggybread.com
Ans. Class.getInstance doesn't call the constructor whereas if we create an object using new operator , we need to have a matching constructor or copiler should provide a default constructor.

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

   Like         Discuss         Correct / Improve     java   constructor   object creation   default constructor   getinstance   new operator


 Q36. What is an Object ?Core Java
Admin
info@buggybread.com
Ans. Object is a run time entity whose state is stored in fields and behavior is shown via methods. Methods operate on an object's internal state and serve as the primary mechanism for object-to-object communication.

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

   Like         Discuss         Correct / Improve     java   oops   objects   basic interview question     Asked in 1 Companies      basic        frequent


 Q37. Variable of the boolean type is automatically initialized as?Core Java
Admin
info@buggybread.com
Ans. The default value of the boolean type is false.

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

   Like         Discuss         Correct / Improve     java   data type   boolean   initialization   default object construction   default constructor   default value


 Q38. In a case where there are no instance variables what does the default constructor initialize?Core Java
Admin
info@buggybread.com
Ans. Java expects the superclass ( Object Class ) constructor to be called while creation of any object. So super constructor is called in case there are no instance variables to initialize.

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

   Like         Discuss         Correct / Improve     java   constructor   object creation   default constructor   super

Try 1 Question(s) Test


 Q39. Will this code compile fine ?

ObjectOutputStream objectOutputStream = new ObjectOutputStream(new FileOutputStream(new File("newFile.txt")));
Core Java
Admin
info@buggybread.com
Ans. Yes.

 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   objectoutputstream   fileoutputstream   yesno  file handling


 Q40. Can we declare Entity class as final ?Hibernate
Admin
info@buggybread.com
Ans. Yes but as Hibernate creates the Proxy Classes inherited from the Entity Classes to communicate with Database for lazy initialization. Declaring entity classes as final will prohibit communication with database lazily and hence will be a performance hit.

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

   Like         Discuss         Correct / Improve     hibernate   proxy objects   proxy classes   entity hibernate


 Q41. Can we extend an Enum ?Core Java
Admin
info@buggybread.com
Ans. No. Enums are final by design.

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

   Like         Discuss         Correct / Improve     java   enums   inheritance  object oriented programming (oops)  oops concepts   yes-no     Asked in 1 Companies      intermediate


 Q42. Is this Polymorphism ?

Map<String, List<String>> inventoryManagerCountMap = new HashMap<String, ArrayList<String>>();
Core Java
Admin
info@buggybread.com
Ans. No. This will result in compilation error as Polymorphism cannot be performed on Object types.

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

   Like         Discuss         Correct / Improve     java   polymorphism  object oriented programming (oops)  oops concepts


 Q43. What are stateless objects ? How are they different from immutable objects ? Which of these two is thread safe ?Object Oriented Programming
Admin
info@buggybread.com
Ans. Stateless objects are the objects without instance fields (instance variables). The class may have compile time constants i.e static final fields.Immutable objects are the objects which have state but the state cannot be changed after initialization. Both are Thread safe.

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

   Like         Discuss         Correct / Improve     java   stateless objects   immutable  immutability objects   objects   singleton scope


 Q44. What are advantages of stateless and / or immutable objects ?Object Oriented Programming
Admin
info@buggybread.com
Ans. They can be shared across multiple threads as they are thread safe.

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

   Like         Discuss         Correct / Improve     java   stateless objects   immutable  immutability objects   objects


 Q45. What will be the output ?Integer a = 10, b =10;Integer c = 10, d = 1000;System.out.println(a == b);System.out.println(c ==d);Core Java
admin
info@buggybread.com
Ans. truefalse

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

   Like         Discuss         Correct / Improve     java   coding   equality   object equality


 Q46. Which of the following do you think is the primary reason you would never use a static class even the application doesn't need multiple requests or threads ?

a. Serialization
b. Runtime Polymorphism
c. Lazy Loading
d. Memory
Anonymous
Ans. Runtime Polymorphism

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

   Like         Discuss         Correct / Improve     static class   static vs singleton   java   oops   objects  Runtime Polymorphism


Must know at all levels. Among Top 10 frequently asked questions in Java. Very frequently asked to fresh graduates or less experienced professionals.
  Q47. What is Inheritance ?Core Java

Ans. Its a facility for code reuse and independent extension wherein a derived class inherits the properties of parent class.

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

   Like         Discuss         Correct / Improve     inheritance  object oriented programming (oops)  oops concepts  oops concepts  java concepts  code reuse  code re-use   classes  derived classes     Asked in 14 Companies      basic        frequent


 Q48. How is static and dynamic polymorphism achieved in Java ?Core Java

Ans. Static polymorphism is the polymorphic resolution identified at compile time and is achieved through function overloading whereas dynamic polymorphism is the polymorphic resolution identified at runtime and is achieved through method overriding.

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

   Like         Discuss         Correct / Improve     static polymorphism  object oriented programming (oops)  oops concepts   dynamic polymorphism  object oriented programming (oops)  oops concepts   polymorphism  object oriented programming (oops)  oops concepts   overloading   overriding   broadridg     Asked in 1 Companies      basic        frequent


 Q49. What will the following code print ?

Integer a = 100, b =100;
Integer c = 1000, d = 1000;
System.out.println(a == b);
System.out.println(c ==d);
Core Java

Ans. false
false

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

   Like         Discuss         Correct / Improve     object equality  code  coding        frequent


  Q50. How is multiple inheritance implemented in Java ?Core Java

Ans. There was no multiple inheritance in java before version 8 as implementing multiple interfaces cannot be termed as inheritance.

With Java 8 , came the concept of default methods wherein the class implementing the interface carries the default implementation from the interface and hence facilitating multiple inheritance.

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

   Like         Discuss         Correct / Improve     multiple inheritance  object oriented programming (oops)  oops concepts   inheritance  object oriented programming (oops)  oops concepts   oops concept     Asked in 10 Companies        frequent


 Q51. Can a lock be acquired on a class? How is it different than the object level lock ?

Ans. Yes, a lock can be acquired on the class. Class level lock is applicable on the whole class and hence on all objects of the class whereas the object level lock is applicable on the respective object.

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

   Like         Discuss         Correct / Improve     synchronization  class level lock  object level lock


 Q52. What is DTO ?2016-06-16 08:30:10

Ans. DTO is Data Transfer Object i.e Pojo which is supposed to move between different layers of software architecture for transferring information. Example could be the object passed from client in case of web service call or the object passed to Persister for Database Persistence.

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

   Like         Discuss         Correct / Improve     DTO   Data Transfer Object      basic        frequent


 Q53. What is DAO ?2016-06-16 08:31:35

Ans. DAO is Data Access Object which is used within Persistence Layer to make Database Transaction. For example , the class holding the Database connection and CRUD methods.

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

   Like         Discuss         Correct / Improve     DAO  Data Access Object      basic        frequent


 Q54. What is POJO ?2016-06-16 08:33:49

Ans. POJO is Plain Java Object that holds only Member Elements , getters are setters and minimal processing on that. The primary purpose of such object is to either transfer information or keeping state for a while. They are not intended to provide any processing or transformation.

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

   Like         Discuss         Correct / Improve     POJO   Plain Java Objects


 Q55. What are VO ?2016-06-16 08:34:25

Ans. VO or Value objects are the objects that are supposed to hold some value. For Example , Integer, Float , Money etc.

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

   Like         Discuss         Correct / Improve     Value Objects


 Q56. What is multilevel inheritance ?Core Java2016-06-23 13:52:50

Ans. Multi Level Inheritance is multi level hierarchy of classes. Here is the example - http://www.buggybread.com/2015/09/java-se-class-diagram-classes-that_603.html

Class RoleList extends ArrayList which in turn extends AbstractList which in turn extends AbstractCollection.

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

   Like         Discuss         Correct / Improve     multilevel inheritance  object oriented programming (oops)  oops concepts  inheritance  object oriented programming (oops)  oops concepts  oops concepts     Asked in 3 Companies      basic

Try 1 Question(s) Test


 Q57. Does default methods introduce multiple inheritance and the Diamond problem in Java 8 ?Core Java2016-07-20 17:16:28

Ans. Default methods results in multiple inheritance of behavior and not of state. In case we try to implement multiple interfaces with default method having same name and signature, and don't override it in implementation class, it will throw an error.

For example -

interface MyInterface {
public void default myMethod(){
}
}

interface MyInterface2 {
public void default myMethod(){
}
}

class MyClass implements MyInterface,MyInterface2 {
}

This code will compilation error "Duplicate Default Method"

if we specify the definition of myMethod() in myClass, compiler won't complain and there is no conflict and MyClass can use overridden definition. But if we don't override myMethod() in MyClass, Java would be in conflict as to what definition should be carried to MyClass and hence throws compilation error.

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

   Like         Discuss         Correct / Improve     default methods  java 8  multiple inheritance  object oriented programming (oops)  oops concepts  diamond problem   interfaces


 Q58. Why do we use a copy constructor ?2016-07-21 08:28:52

Ans. Copy Constructor is used for creating a duplicate of another object. Duplicate object will have the same state of the copied object but will have independent values in different memory locations. Copy Constructor can be useful to create duplicates of immutable objects as the Original cannot be tampered. Moreover It can be useful if base copies are required for individual requests in threading.

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

   Like         Discuss         Correct / Improve     copy constructor  clone  cloning object   immutable  immutability  immutability


 Q59. Does it make sense to clone an object which is supposed to be immutable ?Design2016-07-28 20:54:59

Ans. It make sense only if we intend to modify either of the object and would like to preserve original state in other. Otherwise we can reuse the original object by making it singleton.

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

   Like         Discuss         Correct / Improve     clone  clone objects  prototype design pattern   immutable  immutability  immutability  cloning


 Q60. Can we access private members of the parent class ? i.e Are private members of the class visible in the derived class ?Core Java2016-08-04 09:24:34

Ans. No, If both Parent and Derived are outer classes.

public class Vehicle {
private static String manufacturingDate = "2016";
}

public class Car extends Vehicle{
public static void main(String args[]){
System.out.println(manufacturingDate); // error - The field Vehicle.manufacturingDate is not visible
}
}

Yes, If derived is the inner class of Parent.

public class Vehicle {
private static String manufacturingDate = "2016";
static public class Car extends Vehicle{
public static void main(String args[]){
System.out.println(manufacturingDate); // no problem
}
}
}

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

   Like         Discuss         Correct / Improve     private members   private methods   private variables   inheritance  object oriented programming (oops)  oops concepts   members visibility   inner classes  nexted classes      basic        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: