Core Java Interview Questions

  1. What is static block?
  2. What is Constructor?
  3. What is Encapsulation?
  4. What is Collection API?
  5. What is an abstract class?
  6. What is transient variable?
  7. What are wrapped classes?
  8. What are Access Specifies?
  9. What is method overloading?
  10. Why Errors are Not Checked?
  11. What is the use of finally block?
  12. What are the uses of final method?
  13. Which is super class of Exception?
  14. What is main purpose of interface?
  15. Explain the user defined Exceptions?
  16. What do u mean constructor in java?
  17. What do u mean by “method” in java?
  18. why java uses singly rooted heirarchy?
  19. How can you force garbage collection?
  20. Can we create an object for an interface?
  21. What is the difference throw and throws?
  22. Can overloaded methods be override too?
  23. Is it possible to override the main method?
  24. What are the principle concepts of OOPS?
  25. How does Java implement polymorphism?
  26. Explain the usage of the keyword transient?
  27. Explain the significance of try-catch blocks?
  28. Why Runtime Exceptions are Not Checked?
  29. What are Access Specifies available in Java?
  30. What is a local, member and a class variable?
  31. What do you understand by Synchronization?
  32. Why operator overloading is not there in java?
  33. Can we have the try block without catch block?
  34. What are the different ways to handle exceptions?
  35. What is the difference between throw and throws?
  36. How does the Java default constructor be provided?
  37. Why threads block or enter to waiting state on I/O?
  38. How are this () and super () used with constructors?
  39. What is the difference between yield () and sleep ()?
  40. What are the advantages of using exception handling?
  41. How do you prevent a method from being overridden?
  42. What modifiers are allowed for methods in an Interface?
  43. What is difference between an Abstract class and Interface?
  44. What are the differences between Contructors and Methods?
  45. What is similarities between an Abstract class and Interface?
  46. Can there be an abstract class with no abstract methods in it?
  47. What is runtime polymorphism or dynamic method dispatch?
  48. What are the similarities between an array and an Array List?
  49. What is the difference between abstraction and encapsulation?
  50. What is the difference between static and non-static variables?
  51. How to invoke a super class version of an Overridden method?
  52. What are the differences between Interface and Abstract class?
  53. What is the initial state of a thread when it is created and started?
  54. Why would you use a synchronized block vs. synchronized method?
  55. What is the difference between time slicing and preemptive scheduling?
  56. What are the differences between method overloading and method overriding?
  57. When you declare a method as abstract, can other no abstract methods access it?
  58. What if there is a break or return statement in try block followed by finally block?
  59. How many ways to create Thread and which one is good? Runnable interface or Thread class?
  60. Can we declare an anonymous class as both extending a class and implementing an interface?