1000+ Java Interview Questions and Answers

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This page has a one-stop shop of all the interview questions on Java, Spring Boot, Microservices, Full-Stack development, and more.

These are interview questions and answers based on my past 12+ years of experience in Java development, so I am sure you may get these questions in the interviews.

1. Java Interview Questions and Answers

Java Basics and OOPs Concepts

Java Collections Interview Questions and Answers

Java Coding Interview Questions and Answers

Java 8 Interview Questions and Answers

2. Spring and Spring Boot Interview Questions and Answers

3. JPA/Hibernate Interview Questions and Answers

4. Java Programs for Interviews

Note that these programs are frequently asked in Java interviews. All these Java programs have step-by-step explanations along with their output.

  1. Java ArrayList Programs
  2. Java Number Programs
  3. Java Array Programs
  4. Java 8 Programs

Java Programs on Numbers

  1. Java Program to Find Sum of Natural Numbers
  2. Java Program to Reverse a Number
  3. Java Program to Find Prime Numbers
  4. Java Program to Check Armstrong Number
  5. Java Program to Count the Number of Digits in a Number
  6. Java Program for Prime Numbers Within a Range
  7. Java Program to Find the Largest of Three Numbers
  8. Java Program to Check if a Number is Prime
  9. Java Program to Find the Fibonacci Series
  10. Java Program to Check if a Number Is Positive or Negative
  11. Java Program to Calculate Average Using Arrays
  12. Java Program to Check if a Year is a Leap Year
  13. Java Program to Find Factorial Using Recursion
  14. Java Program to Find GCD of Two Numbers
  15. Java Program to Find Strong Number
  16. Java Program to Find LCM of Two Numbers
  17. Java Program to Check Palindrome Number
  18. Java Program to Remove All Whitespaces from a String
  19. Java Program to Swap Two Numbers Without Using a Temp Variable
  20. Java Program to Find the Second Largest Number in an Array
  21. Java Program to Perform Matrix Multiplication
  22. Java Program to Find Transpose of a Matrix
  23. Java Program to Add Two Matrices
  24. Java Program to Display Characters from A to Z using Loop
  25. Java Program to Check if a Given Number is Perfect Square

Java String Programs with Output

  1. Java Program to Find the First Non-repeated Character in a String
  2. Java Program to Check Palindrome String
  3. Java Program to Find Duplicate Characters in a String
  4. Java Program to Find Duplicate Words in a String
  5. Java Program to Find All the Permutations of a String
  6. Java Program to Count Occurrences of Words in a String
  7. Java Program to Count the Occurrences of Each Character
  8. Java Program to Count Vowels and Consonants in a String
  9. Java program to Count the Number of Duplicate Words in a String
  10. Java Program to Count Number of Words in Given String
  11. Java Program to Count the Number of Occurrences of Substring in a String
  12. Java Program to Count the Occurrences of Each Character in String
  13. Java Program to Merge Two String Arrays
  14. Java Program to Remove Duplicate Words from String
  15. Java Program to Reverse a String(5 ways)
  16. Java Program to Reverse Each Word of a String
  17. Java Program to Swap Two Strings
  18. How to Check if the String Contains Only Digits
  19. How to Check if the String Contains Only Letters
  20. How to Check If the String Contains Only Letters or Digits
  21. Java Program to Check if a String is Empty or Null
  22. Java Program to Find Maximum Occurring Character in String
  23. Java Program To Count the Occurrences of Each Character Using HashMap
  24. Java Program to Add Characters to a String
  25. Java Program to Reverse a List
  26. Java Program to Find the Occurrence of Words in a String using HashMap

Java Array Programs with Output

  1. Java Program to Reverse an Array Without Using Another Array
  2. Java Program to Find Duplicate Elements in an Array
  3. Java Program to Find Largest Number in an Array
  4. Java Program to Check the Equality of Two Arrays
  5. Java Program to Sort the Array Elements in Descending Order

Java 8 Programs with Output

  1. Java 8 Program to Find the Frequency of Each Character in a Given String
  2. Java 8 Program to Find the Maximum Number and Minimum Number in a List
  3. Java 8 Program to Find the Second Largest Number in the List of Integers
  4. Java 8 Program to Find the Age of a Person if the Birthday Date has Given
  5. Java 8 Program to Find the Sum of All Digits of a Number
  6. Java 8 Program to Print Even Numbers from a List
  7. Java 8 Program to Remove Duplicate Elements from a List
  8. Java 8 Program to Retrieve Last Element of a List of Strings
  9. Java 8 Program to Reverse Each Word of String
  10. Java 8 Program to Sort List of Strings Alphabetically
  11. Java 8 Programs for Interview | Java 8 Interview Coding Questions and Answers
  12. Java 8 Program To Count Characters in a String
  13. Java 8 Program To Find First Repeated Character in a String
  14. Java 8 Program to Concatenate Two Streams
  15. Java 8 Program To Reverse a String
  16. Java 8 Program To Find Prime Number
  17. Java 8 Program To Find the Minimum and Maximum Number of a Stream

Java Pattern Programs with Output

  1. Java Program for Diamond Shape Pattern
  2. Java Program to Print Character Pyramid Pattern
  3. Java Program to Print a Pyramid
  4. Java Program to Print an Inverted Pyramid
  5. Java Program to Print a Hollow Pyramid
  6. Java Program to Print a Diamond Pattern
  7. Java Program to Print a Right Triangle Star Pattern
  8. Java Program to Print an Inverted Right Triangle Star Pattern
  9. Java Program to Print a Left Triangle Star Pattern
  10. Java Program to Print a Pascal's Triangle
  11. Java Program to Print a Fibonacci Pyramid
  12. Java Program to Print a Number Pyramid
  13. Java Program to Print a Reverse Number Pyramid
  14. Java Program to Print a Hollow Square Pattern
  15. Java Program to Print a Cross (X) Pattern
  16. Java Program to Print a Plus (+) Pattern
  17. Java Program to Print a Butterfly Pattern
  18. Java Program to Print a Diamond Shape with Numbers
  19. Java Program to Print an Alphabet Pyramid
  20. Java Program to Print a Heart Shape Star Pattern

Java Programs on OOP (Object-Oriented Programming) with Output

  1. Java Program to Calculate Salary of an Employee
  2. Java Program to Calculate Gross Salary of Employee

Java Programs on Data Structures and Algorithms

  1. Java Program to Reverse a Linked List
  2. Detecting a Cycle in a Linked List Using Java
  3. Finding the Middle Element of a Linked List using Java
  4. Merging Two Sorted Linked Lists using Java
  5. Queue Implementation in Java Using Array
  6. Queue Implementation in Java Using ArrayList
  7. Queue Implementation in Java Using LinkedList
  8. Queue Implementation in Java Using Two Stacks
  9. Priority Queue Implementation in Java Using Linked List
  10. Linked List Implementation in Java Using Arrays
  11. Doubly Linked List Implementation in Java
  12. Circular Linked List Implementation in Java
  13. Deque Implementation in Java
  14. Finding the Height of a Binary Tree in Java
  15. Determining if a Binary Tree is Balanced in Java
  16. Implementing Binary Search Tree (BST) Operations in Java
  17. Finding the Lowest Common Ancestor in a BST using Java

5. Top Interview Java Questions on Differences

  1. ArrayDeque vs LinkedList in Java
  2. ConcurrentHashMap vs HashMap in Java
  3. PriorityQueue vs LinkedList in Java
  4. WeakHashMap vs HashMap in Java
  5. IdentityHashMap vs HashMap in Java
  6. CopyOnWriteArraySet vs HashSet in Java
  7. SynchronizedMap vs ConcurrentHashMap in Java
  8. TreeMap vs LinkedHashMap in Java
  9. EnumSet vs HashSet in Java
  10. EnumMap vs HashMap in Java
  11. Queue vs Stack in Java
  12. NavigableMap vs SortedMap in Java
  13. NavigableSet vs SortedSet in Java
  14. Iterable vs Collection in Java
  15. Difference between final, finally, and finalize in Java
  16. Difference between Error and Exception in Java
  17. Checked Exception vs Unchecked Exception in Java
  18. Difference between Object and Class in Java
  19. Difference between Runnable and Thread in Java
  20. Difference between == and equals() method in Java
  21. static variable vs instance variable in Java
  22. Abstract Class vs Interface in Java
  23. fail-fast vs fail-safe Iterators in Java
  24. Difference between break and continue in Java
  25. Difference between constructors and methods in Java
  26. Difference between throws and throw in Java
  27. synchronized block vs synchronized method in Java
  28. while loop vs do-while loop in Java
  29. Immutable vs Mutable objects in Java
  30. Difference between Annotation and Enum in Java
  31. static block vs static method in Java
  32. Marker Interface vs Functional Interface in Java
  33. Shallow Copy vs Deep Copy in Java
  34. Composition vs Inheritance in Java
  35. Difference between volatile and transient in Java
  36. Difference between sleep() and wait() in Java
  37. Difference between & and && in Java
  38. Difference between | and || in Java
  39. Switch-Case vs If-Else in Java?
  40. Default Method vs Static Method in Java Interfaces
  41. For Loop vs Enhanced For Loop (for-each) in Java
  42. Difference between Servlet and JSP in Java
  43. Difference between ORM and JDBC in Java
  44. hashCode() vs equals() in Java
  45. Difference between Throwable and Exception in Java
  46. Difference between import and package in Java
  47. Daemon Thread vs User Thread in Java
  48. Difference between literal and constant in Java
  49. Difference between this and super Keyword in Java
  50. Lambda vs Anonymous Class in Java
  51. Stack vs Heap Memory in Java
  52. Runnable vs Callable in Java
  53. Difference between Path and File in Java NIO
  54. count() vs length() in Java Stream API
  55. Intermediate vs Terminal Operations in Java Stream API
  56. Executor vs ExecutorService in Java
  57. Primitive Data Type vs Reference Data Type in Java
  58. Compiler vs Interpreter in Java
  59. Difference between WAR and JAR in Java
  60. Dependency Injection vs Factory Pattern in Java
  61. Difference between PUT and POST in Java REST API
  62. Static Nested Class vs Inner Class in Java
  63. Difference between GET and POST in Java Web Services
  64. Encapsulation vs Abstraction in Java
  65. JPA vs Hibernate in Java with Example
  66. @Bean vs @Component in Spring
  67. @Autowired vs @Resource in Spring
  68. Difference between JDBC and JPA
  69. Difference between Spring Security and OAuth2
  70. Difference between Spring Cloud and Spring Boot
  71. Difference between Spring Boot and Microservices
  72. @RequestParam vs @PathVariable in Spring Boot
  73. @Query vs NamedQuery in JPA
  74. Spring Data JPA vs Hibernate in Java with Example
  75. @Controller vs @RestController in Spring Boot 
  76. Difference Between Source Code and Byte Code in Java 
  77. Difference between Byte Code and Machine Code 
  78. Difference between JIT and JVM in Java
  79. Find the Duration of Difference Between Two Dates in Java

Java 8 Interview Questions on Employee Salary

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