Interview Questions and Answers - Order By Rating Q31. Will this code Work ? If not , Why ? java.util.Calendar c = new java.util.Calendar(); Core Java
Ans. No. It gives the error "Cannot Instantiate the type Calendar". Calendar is an abstract class and hence Calendar object should be instantiated using Calendar.getInstance(). Help us improve. Please let us know the company, where you were asked this question : Like Discuss Correct / Improve  java   date   calendar   abstract class   yes-no Q32. Is java.util.Date an abstract Class ? Is java.util.Calendar an abstract Class ? Core Java
Ans. Date is not a abstract class whereas Calendar is. Help us improve. Please let us know the company, where you were asked this question : Like Discuss Correct / Improve  java   date   calendar   abstract class Q33. Will this code compile ? public class BuggyBread1{ abstract public void test(); } Core Java
Ans. No. It will give the compilation error saying "The abstract method test in type BuggyBread1 can only be defined by an abstract class". We need to declare the class abstract for it to have any abstract method. Help us improve. Please let us know the company, where you were asked this question : Like Discuss Correct / Improve  java   oops   abstract class   abstract methods   java compilation error Q34. Will this Code compile ? abstract public class BuggyBread1{ abstract public void test(){}; } Core Java
Ans. No. This will give a compilation error saying "Abstract methods do not specify a body". Help us improve. Please let us know the company, where you were asked this question : Like Discuss Correct / Improve  java   abstract classes   abstract methods   java compilation error   java coding   java code   coding   yes-no Q35. How is Abstraction implemented in Java ? Core Java
Ans. Abstraction is provided in Java by following ways -
Coding to the ( Interfaces / Abstract Classes ) or contracts
By Encapsulating details within classes and exposing the minimal Door ( few public methods ) Help us improve. Please let us know the company, where you were asked this question : Like Discuss Correct / Improve  java   oops concepts   abstraction   interfaces   abstract class   encapsulation  object oriented programming (oops)  oops concepts Asked in 3 Companies basic   frequent Very Frequently asked. Have been asked in HCL Technologies very frequently ( based on 3 feedback ). Among first few questions in many interviews. Q36. Differences between abstract class and interface ? Core Java
Ans. Abstract classes can have both abstract methods ( method declarations ) as well as concrete methods ( inherited to the derived classes ) whereas Interfaces can only have abstract methods ( method declarations ).
A class can extend single abstract class whereas it can implement multiple interfaces. Help us improve. Please let us know the company, where you were asked this question : Like Discuss Correct / Improve  java   classes   abstract class   interfaces   abstract class vs interface   abstract classes vs interfaces Asked in 82 Companies basic   frequent Q37. What is ADT or Abtstract Data Type ? Core Java
Ans. ADT is a container which holds different types of objects with specifications.
For example - Stack, Array, Liked list, Tree Help us improve. Please let us know the company, where you were asked this question : Like Discuss Correct / Improve  data types  abstract data types Q38. Why can't we declare a class abstract as well as final ? Core Java
Ans. Abstract means that the class is only meant to be subclassed whereas final means that it cannot be subclassed so both concepts - abstract and final are actually mutually exclusive and hence not permitted together. Help us improve. Please let us know the company, where you were asked this question : Like Discuss Correct / Improve  abstract   final   java keywords Asked in 1 Companies Q39. In the following code , how many methods needs to be implemented in Class B ?
public interface A{
public void method1();
public void method2();
public void method3();
}
abstract class B implements A{
} Core Java
Ans. As Class B has been declared abstract , we can either implement any of these methods and just declare rest of them abstract. Help us improve. Please let us know the company, where you were asked this question : Like Discuss Correct / Improve  interfaces  abstract classes  code  coding Try 2 Question(s) Test Q40. What should a class do if its extending an abstract class ? Core Java
Ans. It should either implement the abstract methods or re-declare them abstract. Help us improve. Please let us know the company, where you were asked this question : Like Discuss Correct / Improve  abstract class Asked in 2 Companies Basic   Frequent a. Abstract Class is only meant to be sub classed and not supposed to be instantiated. b. Abstract class handlers can be used to handle derived class objects. c. We can't have an abstract class without abstract methods. d. Abstract class has member elements. Ans.c. We can't have an abstract class without abstract methods.
Q42. Which of the following can be declared abstract ? Core Java
a. static methods b. instance methods c. static variable d. instance variablesAns.b. instance methods