{"id":504,"date":"2026-04-29T18:15:35","date_gmt":"2026-04-29T18:15:35","guid":{"rendered":"https:\/\/logicnextgen.com\/tutorials\/?page_id=504"},"modified":"2026-05-23T16:33:06","modified_gmt":"2026-05-23T16:33:06","slug":"java-interview-questions-answers","status":"publish","type":"page","link":"https:\/\/logicnextgen.com\/tutorials\/java-interview-questions-answers\/","title":{"rendered":"Java Interview Questions & Answers"},"content":{"rendered":"\n

Java Interview Questions & Answers<\/strong><\/p>\n\n\n\n

1. What is Java?<\/strong><\/h3>\n\n\n\n

Java is a high-level, object-oriented, platform-independent programming language used for developing web, desktop, mobile, and automation applications.<\/p>\n\n\n\n

2. What are the features of Java?<\/strong><\/h3>\n\n\n\n
    \n
  • Platform independent<\/li>\n\n\n\n
  • Object-oriented<\/li>\n\n\n\n
  • Secure<\/li>\n\n\n\n
  • Robust<\/li>\n\n\n\n
  • Multithreaded<\/li>\n\n\n\n
  • Portable<\/li>\n<\/ul>\n\n\n\n

    3. What are variables in Java?<\/strong><\/h3>\n\n\n\n

    Variables are containers used to store data values.<\/p>\n\n\n\n

    Example:<\/p>\n\n\n\n

    int age = 25;<\/code><\/pre>\n\n\n\n
    4. What are data types in Java?<\/strong><\/h3>\n\n\n\n
    Two types:<\/p>\n\n\n\n
      \n
    • Primitive \u2192 int, char, boolean<\/li>\n\n\n\n
    • Non-primitive \u2192 String, Array, Class<\/li>\n<\/ul>\n\n\n\n
      5. What is the difference between primitive and non-primitive data types?<\/strong><\/h3>\n\n\n\n
      Primitive<\/strong><\/td>Non-Primitive<\/strong><\/td><\/tr>
      Stores value<\/td>Stores reference<\/td><\/tr>
      Fixed size<\/td>Dynamic size<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
      6. What is type casting in Java?<\/strong><\/h3>\n\n\n\n
      Converting one datatype into another datatype.<\/p>\n\n\n\n
      Example:<\/p>\n\n\n\n
      double d = 10.5;\nint i = (int)d;<\/code><\/pre>\n\n\n\n
      7. What are operators in Java?<\/strong><\/h3>\n\n\n\n
      Operators perform operations on variables.<\/p>\n\n\n\n
      Examples:<\/p>\n\n\n\n
        \n
      • Arithmetic (+)<\/li>\n\n\n\n
      • Logical (&&)<\/li>\n\n\n\n
      • Relational (>)<\/li>\n<\/ul>\n\n\n\n
        8. What is the difference between <\/strong>==<\/strong> and <\/strong>.equals()<\/strong>?<\/strong><\/h3>\n\n\n\n
        ==<\/strong><\/td>.equals()<\/strong><\/td><\/tr>
        Compares memory reference<\/td>Compares values<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
        9. What are OOPs concepts in Java?<\/strong><\/h3>\n\n\n\n
          \n
        • Encapsulation<\/li>\n\n\n\n
        • Inheritance<\/li>\n\n\n\n
        • Polymorphism<\/li>\n\n\n\n
        • Abstraction<\/li>\n<\/ul>\n\n\n\n
          10. What is encapsulation?<\/strong><\/h3>\n\n\n\n
          Encapsulation means wrapping data and methods together in a single class and restricting direct access using private variables.<\/p>\n\n\n\n
          11. What is inheritance?<\/strong><\/h3>\n\n\n\n
          Inheritance allows one class to acquire properties and methods of another class using extends keyword.<\/p>\n\n\n\n
          12. What is polymorphism?<\/strong><\/h3>\n\n\n\n
          Polymorphism means one method can perform different actions based on the object.
          Types:<\/p>\n\n\n\n
            \n
          • Overloading<\/li>\n\n\n\n
          • Overriding<\/li>\n<\/ul>\n\n\n\n
            13. What is abstraction?<\/strong><\/h3>\n\n\n\n
            Abstraction means hiding implementation details and showing only required functionality.
            <\/p>\n\n\n\n
            14. What is the difference between abstraction and encapsulation?<\/strong><\/h3>\n\n\n\n
            Abstraction<\/strong><\/td>Encapsulation<\/strong><\/td><\/tr>
            Hides implementation<\/td>Hides data<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
            15. What is method overloading?<\/strong><\/h3>\n\n\n\n
            Method overloading means creating multiple methods with same name but different parameters.
            <\/p>\n\n\n\n
            16. What is method overriding?<\/strong><\/h3>\n\n\n\n
            Method overriding means redefining parent class method in child class with same signature.
            <\/p>\n\n\n\n
            17. What is the difference between overloading and overriding?<\/strong><\/h3>\n\n\n\n
            Overloading<\/strong><\/td>Overriding<\/strong><\/td><\/tr>
            Same class<\/td>Parent-child class<\/td><\/tr>
            Different parameters<\/td>Same parameters<\/td><\/tr>
            Compile-time polymorphism<\/td>Runtime polymorphism<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
            18. What is an interface in Java?<\/strong><\/h3>\n\n\n\n
            An interface is a blueprint containing abstract methods that must be implemented by classes.
            <\/p>\n\n\n\n
            19. What is an abstract class?<\/strong><\/h3>\n\n\n\n
            An abstract class is a class declared using abstract keyword. It can contain abstract and non-abstract methods<\/p>\n\n\n\n
            20. What is the difference between interface and abstract class?<\/strong><\/h3>\n\n\n\n
            Interface<\/strong><\/td>Abstract Class<\/strong><\/td><\/tr>
            Supports multiple inheritance<\/td>Partial abstraction<\/td><\/tr>
            Mostly abstract methods<\/td>Can contain concrete methods<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
            21. What is constructor in Java?<\/strong><\/h3>\n\n\n\n
            Constructor initializes object.<\/p>\n\n\n\n
            22. What is constructor overloading?<\/strong><\/h3>\n\n\n\n
            A constructor is a special method used to initialize objects.
            <\/p>\n\n\n\n
            23. What is constructor overloading?<\/strong><\/p>\n\n\n\n
            Creating multiple constructors with different parameters is called constructor overloading<\/p>\n\n\n\n
            23. What is the difference between constructor and method?<\/strong><\/h3>\n\n\n\n
            Constructor<\/strong><\/td>Method<\/strong><\/td><\/tr>
            Initializes object<\/td>Performs operations<\/td><\/tr>
            Same name as class<\/td>Any valid name<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
            24. What is <\/strong>this<\/strong> keyword?<\/strong><\/h3>\n\n\n\n
            Refers to current class object.<\/p>\n\n\n\n
            25. What is <\/strong>super<\/strong> keyword?<\/strong><\/h3>\n\n\n\n
            super refers to parent class object or constructor.<\/p>\n\n\n\n
            26. What is static keyword in Java?<\/strong><\/h3>\n\n\n\n
            static belongs to class instead of object.<\/p>\n\n\n\n
            27. What is final keyword in Java?<\/strong><\/h3>\n\n\n\n
            Used to:<\/p>\n\n\n\n
              \n
            • Prevent inheritance<\/li>\n\n\n\n
            • Prevent overriding<\/li>\n\n\n\n
            • Declare constants<\/li>\n<\/ul>\n\n\n\n
              28. Can we override static or final methods?<\/strong><\/h3>\n\n\n\n
              No, static and final methods cannot be overridden.<\/p>\n\n\n\n
              29. What is String in Java?<\/strong><\/h3>\n\n\n\n
              String is a sequence of characters used to store text.
              <\/p>\n\n\n\n
              30. What is the difference between String, StringBuffer, and StringBuilder?<\/strong><\/h3>\n\n\n\n
              String<\/strong><\/td>StringBuffer<\/strong><\/td>StringBuilder<\/strong><\/td><\/tr>
              Immutable<\/td>Mutable<\/td>Mutable<\/td><\/tr>
              Slow<\/td>Thread-safe<\/td>Faster<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
              31. Why is String immutable in Java?<\/strong><\/h3>\n\n\n\n
              For security, thread safety, and performance.<\/p>\n\n\n\n
              32. What is string pooling?<\/strong><\/h3>\n\n\n\n
              Java stores string literals in common memory called String Pool.<\/p>\n\n\n\n
              33. What is the difference between <\/strong>equals()<\/strong> and <\/strong>equalsIgnoreCase()<\/strong>?<\/strong><\/h3>\n\n\n\n
              equals()<\/strong><\/td>equalsIgnoreCase()<\/strong><\/td><\/tr>
              Case-sensitive<\/td>Ignores case<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
              34. How do you reverse a string in Java?<\/strong><\/h3>\n\n\n\n
              Using StringBuilder:<\/p>\n\n\n\n
              String rev = new StringBuilder(str).reverse().toString();<\/p>\n\n\n\n
              35. How do you remove duplicates from a string?<\/strong><\/h3>\n\n\n\n
              Duplicates can be removed using loops, Set collection, or HashSet.<\/p>\n\n\n\n
              36. How do you count characters in a string?<\/strong><\/h3>\n\n\n\n
              Using length() method.<\/p>\n\n\n\n
              str.length();<\/p>\n\n\n\n
              37. What is an array in Java?<\/strong><\/h3>\n\n\n\n
              An array is a collection of elements of the same datatype stored in a single variable. It is used to store multiple values together using index positions.<\/p>\n\n\n\n
              38. What is ArrayList?<\/strong><\/h3>\n\n\n\n
              ArrayList is a class in Java Collection Framework used to store dynamic collections of elements. Unlike arrays, its size can grow or shrink automatically.<\/p>\n\n\n\n
              39. What is the difference between Array and ArrayList?<\/strong><\/h3>\n\n\n\n
              Array<\/td>ArrayList<\/td><\/tr>
              Fixed size<\/td>Dynamic size<\/td><\/tr>
              Stores primitives<\/td>Stores objects<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
              40. What is the difference between List, Set, and Map?<\/strong><\/h3>\n\n\n\n
              <\/p>\n\n\n\n
              41. What is HashMap in Java?<\/strong><\/h3>\n\n\n\n
              Stores key-value pairs<\/p>\n\n\n\n
              42. What is the difference between HashMap and Hashtable?<\/strong><\/h3>\n\n\n\n
              HashMap<\/strong><\/td>Hashtable<\/strong><\/td><\/tr>
              Not synchronized<\/td>Synchronized<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
              43. What is the difference between HashSet and TreeSet?<\/strong><\/h3>\n\n\n\n
              HashSet<\/strong><\/td>TreeSet<\/strong><\/td><\/tr>
              Unordered<\/td>Sorted<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
              44. What is Iterator in Java?<\/strong><\/h3>\n\n\n\n
              Used to traverse collection elements.<\/p>\n\n\n\n
              45. What is the difference between Iterator and ListIterator?<\/strong><\/h3>\n\n\n\n
              Iterator<\/strong><\/td>ListIterator<\/strong><\/td><\/tr>
              Forward only<\/td>Forward & backward<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
              46. What is Collection Framework in Java?<\/strong><\/h3>\n\n\n\n
              Framework containing classes\/interfaces for storing data.<\/p>\n\n\n\n
              47. What is Comparable and Comparator?<\/strong><\/h3>\n\n\n\n
              Comparable<\/strong><\/td>Comparator<\/strong><\/td><\/tr>
              Natural sorting<\/td>Custom sorting<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
              48. What is the difference between ArrayList and LinkedList?<\/strong><\/h3>\n\n\n\n
              ArrayList<\/strong><\/td>LinkedList<\/strong><\/td><\/tr>
              Faster retrieval<\/td>Faster insertion\/deletion<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
              49. What is exception handling in Java?<\/strong><\/h3>\n\n\n\n
              Mechanism to handle runtime errors.<\/p>\n\n\n\n
              50. What is the difference between checked and unchecked exceptions?<\/strong><\/h3>\n\n\n\n
              Checked<\/strong><\/td>Unchecked<\/strong><\/td><\/tr>
              Compile-time<\/td>Runtime<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
              51. What is try-catch block?<\/strong><\/h3>\n\n\n\n
              Used to handle exceptions.<\/p>\n\n\n\n
              52. What is finally block?<\/strong><\/h3>\n\n\n\n
              Always executes whether exception occurs or not.<\/p>\n\n\n\n
              53. What is throw and throws keyword?<\/strong><\/h3>\n\n\n\n
              throw<\/strong><\/td>throws<\/strong><\/td><\/tr>
              Throws exception<\/td>Declares exception<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
              54. Can finally block execute without catch block?<\/strong><\/h3>\n\n\n\n
              Yes.<\/p>\n\n\n\n
              55. What is NullPointerException?<\/strong><\/h3>\n\n\n\n
              Occurs when accessing null object.<\/p>\n\n\n\n
              56. What is exception propagation?<\/strong><\/h3>\n\n\n\n
              Passing exception from one method to another.<\/p>\n\n\n\n
              57. What is file handling in Java?<\/strong><\/h3>\n\n\n\n
              Reading and writing files using Java classes.<\/p>\n\n\n\n
              58. How do you read data from a file in Java?<\/strong><\/h3>\n\n\n\n
              Using:<\/p>\n\n\n\n
                \n
              • BufferedReader<\/li>\n\n\n\n
              • Scanner<\/li>\n\n\n\n
              • FileReader<\/li>\n<\/ul>\n\n\n\n
                59. How do you write data into a file?<\/strong><\/h3>\n\n\n\n
                Using FileWriter or BufferedWriter.<\/p>\n\n\n\n
                60. What is BufferedReader?<\/strong><\/h3>\n\n\n\n
                Used to read text efficiently.<\/p>\n\n\n\n
                61. What is FileInputStream and FileOutputStream?<\/strong><\/h3>\n\n\n\n
                Used to read\/write byte data.<\/p>\n\n\n\n
                62. What is multithreading in Java?<\/strong><\/h3>\n\n\n\n
                Executing multiple threads simultaneously.<\/p>\n\n\n\n
                63. What is thread in Java?<\/strong><\/h3>\n\n\n\n
                Smallest unit of execution.<\/p>\n\n\n\n
                64. What is the difference between process and thread?<\/strong><\/h3>\n\n\n\n
                Process<\/strong><\/td>Thread<\/strong><\/td><\/tr>
                Independent execution<\/td>Part of process<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
                65. How do you create a thread in Java?<\/strong><\/h3>\n\n\n\n
                Using:<\/p>\n\n\n\n
                  \n
                • Thread class<\/li>\n\n\n\n
                • Runnable interface<\/li>\n<\/ul>\n\n\n\n
                  66. What is synchronization?<\/strong><\/h3>\n\n\n\n
                  Prevents multiple threads accessing shared resources simultaneously.<\/p>\n\n\n\n
                  67. What is thread sleep?<\/strong><\/h3>\n\n\n\n
                  Pauses thread execution temporarily.<\/p>\n\n\n\n
                  68. What is the difference between <\/strong>start()<\/strong> and <\/strong>run()<\/strong>?<\/strong><\/h3>\n\n\n\n
                  start()<\/strong><\/td>run()<\/strong><\/td><\/tr>
                  Creates new thread<\/td>Executes normally<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
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                  1. What is a Constructor in Java?<\/strong><\/p>\n\n\n\n
                  A constructor in Java<\/strong> is a special block of code used to initialize an object when it is created<\/strong>.<\/p>\n\n\n\n