1000+ Java Interview Questions and Answers

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

1. Java main() Method Interview Questions with Answers
2. Java Programs Asked in Interview
3. Java Array Interview Questions and Answers
4. Java String Interview Questions and Answers
5. String vs StringBuffer in Java
6. String vs StringBuilder vs StringBuffer in Java
7. Java Exception Handling Interview Questions and Answers
8. OOPS Interview Questions and Answers
9. Java Design Patterns Interview Questions
10. Java OOPS Concepts Interview Questions and Answers for Beginners and Experienced
11. Top Java 11 Interview Questions
12. Top Java 17 Interview Questions
13. Java 21 Interview Questions

Java Collections Interview Questions and Answers

1. Difference Between List and Set in Java
2. Difference Between Collection and Collections in Java
3. Difference Between Array and ArrayList in Java
4. Difference between ArrayList and LinkedList in Java
5. Difference Between HashSet and LinkedHashSet in Java
6. Difference Between HashSet and TreeSet in Java
7. HashSet vs LinkedHashSet vs TreeSet in Java
8. Difference Between HashMap and HashTable in Java
9. Difference Between HashSet and HashMap in Java
10. HashMap vs LinkedHashMap in Java
11. Difference between HashMap, LinkedHashMap, and TreeMap in Java
12. Collections vs Streams in Java
13. How does the Size of the ArrayList Increase Dynamically?
14. How To Remove Duplicate Elements From ArrayList In Java?

Java Coding Interview Questions and Answers

1. Java Tricky Coding Interview Questions and Answers
2. Java Coding Interview Questions and Answers for 2-5 Years Experience
3. Java String Tricky Coding Questions and Answers
4. Java OOPS Tricky Coding Questions and Answers
5. Java Array Coding Questions and Answers
6. Java String Coding Questions and Answers
7. Java OOPs Coding Questions and Answers
8. Java Exception Handling Coding Questions and Answers
9. Java Loops Coding Questions and Answers
10. Java Collections Coding Questions and Answers
11. Java Lambda Expressions Coding Questions and Answers
12. Java Streams Coding Questions and Answers
13. Java Functional Interfaces Coding Questions and Answers
14. Java Inheritance Coding Questions and Answers
15. Java Coding Questions and Answers
16. Java Operators Coding Questions and Answers
17. Java Data Types Coding Questions and Answers

Java 8 Interview Questions and Answers

1. Java 8 Interview Interview Questions and Answers
2. Java Stream API Interview Questions and Answers
3. Java Lambda Expressions Interview Questions and Answers
4. Java Functional Interface Interview Questions and Answers

2. Spring and Spring Boot Interview Questions and Answers

1. Spring Core Interview Questions
2. Difference Between Spring and Spring Boot
3. Spring vs Spring MVC vs Spring Boot
4. Spring Boot Interview Questions for 5 Years Experience
5. Spring Boot Interview Questions for 2 Years Experience
6. Spring Boot Microservices Interview Questions and Answers
7. Spring Cloud Interview Questions and Answers
8. Top 10 Spring MVC Interview Questions
9. How Spring MVC Works Internally
10. Difference Between Hibernate and Spring Data JPA
11. Spring Batch Interview Questions

3. JPA/Hibernate Interview Questions and Answers

1. What is the Difference Between JPA and Hibernate?
2. Difference Between save vs persist in Hibernate
3. Difference Between save vs saveOrUpdate in Hibernate
4. Difference Between get vs load in Hibernate
5. Hibernate Interview Questions and Answers
6. JPA Interview Questions and Answers

4. Misc Interview Questions and Answers

1. OAuth 2 Interview Questions
2. Apache Kafka Interview Questions
3. RabbitMQ Interview Questions
4. Top 10 Gradle Interview Questions
5. JSON Interview Questions
6. SOAP Interview Questions
7. WebSocket Interview Questions
8. Kotlin Interview Questions
9. Redis Interview Questions
10. Top 10 Apache Spark Interview Questions
11. Apache Storm Interview Questions
12. TestNG Interview Questions
13. AKS (Azure Kubernetes Service) Interview Questions

5. 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

6. 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

7. Java 8 Interview Questions on Employee Salary

1. Java 8 - Count Male and Female Employees in the Organization
2. Java Program to Print the Name of All Departments in the Organization
3. Java Program to Group the Employees by City
4. Java Program to Group the Employees by Age
5. Java Program To Print Employee Details Whose Age Is Greater Than 28
6. Java Program To Find Maximum Age of Employee
7. Java Program To Print Average Age of Male and Female Employees
8. Java Program To Print the Number of Employees in Each Department
9. Java Program To Find Oldest Employee
10. Java Program To Find Youngest Female Employee
11. Java Program To Find the Department Name Which Has the Highest Number of Employees
12. Java Program To Find the Average Salary of Each Department
13. Java Program To Find if There Any Employees From HR Department
14. Java Program for Highest Experienced Employees in the Organization
15. Java Program To Print Average and Total Salary of the Organization
16. Java Program To Find Highest Salary in the Organisation
17. Java Program To Find Second Highest Salary in the Organisation
18. Java Program To Sort the Employees Salary in the Organisation in Ascending Order
19. Java Program To Sort the Employees Salary in the Organisation in Descending Order

Misc

• AKS (Azure Kubernetes Service) Interview Questions
• TestNG Interview Questions
• Apache Storm Interview Questions
• Top 10 Apache Spark Interview Questions
• Java 21 Interview Questions
• Redis Interview Questions
• Kotlin Interview Questions
• WebSocket Interview Questions
• SOAP Interview Questions
• JSON Interview Questions
• Top 10 Gradle Interview Questions
• RabbitMQ Interview Questions
• Apache Kafka Interview Questions
• OAuth 2 Interview Questions
• Top Java 17 Interview Questions
• Top Java 11 Interview Questions
• Spring Batch Interview Questions