Top Java Interview Questions and Answers - Java, Spring Boot, Microservices, Full-Stack

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

There are interview questions and answers based on my past 12+ years of experience in Java development so I am pretty sure that you will get these questions in the interviews.

1. Java Interview Questions and Answers

• Java main() Method Interview Questions with Answers
• Java Programs Asked in Interview
• Java Array Interview Questions and Answers
• Java String Interview Questions and Answers
• String vs StringBuffer in Java
• String vs StringBuilder vs StringBuffer in Java
• Java Exception Handling Interview Questions and Answers
• OOPS Interview Questions and Answers
• Java Design Patterns Interview Questions
• Java OOPS Concepts Interview Questions and Answers for Beginners and Experienced

Java Collections Interview Questions and Answers

• Difference Between List and Set in Java
• Difference Between Collection and Collections in Java
• Difference Between Array and ArrayList in Java
• Difference between ArrayList and LinkedList in Java
• Difference Between HashSet and LinkedHashSet in Java
• Difference Between HashSet and TreeSet in Java
• HashSet vs LinkedHashSet vs TreeSet in Java
• Difference Between HashMap and HashTable in Java
• Difference Between HashSet and HashMap in Java
• HashMap vs LinkedHashMap in Java
• Difference between HashMap, LinkedHashMap, and TreeMap in Java
• Collections vs Streams in Java
• How does the Size of the ArrayList Increase Dynamically?
• How To Remove Duplicate Elements From ArrayList In Java?

Java Coding Interview Questions and Answers

• Java Tricky Coding Interview Questions and Answers
• Java Coding Interview Questions and Answers for 2-5 Years Experience
• Java String Tricky Coding Questions and Answers
• Java OOPS Tricky Coding Questions and Answers

Java 8 Interview Questions and Answers

• Java 8 Interview Interview Questions and Answers
• Java Stream API Interview Questions and Answers
• Java Lambda Expressions Interview Questions and Answers
• Java Functional Interface Interview Questions and Answers

2. Spring and Spring Boot Interview Questions and Answers

• Spring Core Interview Questions
• Difference Between Spring and Spring Boot
• Spring vs Spring MVC vs Spring Boot
• Spring Boot Interview Questions for 5 Years Experience
• Spring Boot Interview Questions for 2 Years Experience
• Spring Boot Microservices Interview Questions and Answers
• Spring Cloud Interview Questions and Answers
• Top 10 Spring MVC Interview Questions
• How Spring MVC Works Internally
• Difference Between Hibernate and Spring Data JPA

3. JPA/Hibernate Interview Questions and Answers

• What is the Difference Between JPA and Hibernate?
• Difference Between save vs persist in Hibernate
• Difference Between save vs saveOrUpdate in Hibernate
• Difference Between get vs load in Hibernate
• Hibernate Interview Questions and Answers
• JPA 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 explanation along with it's output.

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

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

Java Number Programs with Output

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

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