50 Java Programs for Beginners with Output

50 Java programs with output, organized by topic — the coding questions asked in interviews, written tests, and beginner assignments. Each program links to a full tutorial with code and output. Updated September 2026.

Basic programs

1. Hello World Program in Java — the first program everyone writes.
2. Add Two Numbers — reading input and printing a sum.
3. Check Even or Odd Number — the modulus operator in action.
4. Find the Sum of Digits — loops and arithmetic.
5. Find the Factorial of a Number — recursion vs iteration.
6. Print Prime Numbers — a classic loop exercise.
7. Fibonacci Series Program — the most-asked series question.
8. Find the Area of a Circle — working with constants and doubles.
9. Convert Decimal to Binary — number-system conversion.
10. Convert Binary to Decimal — the reverse conversion.

String programs

11. Reverse a String — the single most-asked string question.
12. Check Whether a String is a Palindrome — two-pointer technique.
13. Print Vowels in a String — character iteration.
14. Check Whether a String Has All Unique Characters — HashSet thinking.
15. Remove Duplicate Characters from a String in O(n) — optimal-time solution.
16. Check Balanced Parentheses in O(n) — the stack classic.

Array programs

17. Find the Missing Number in an Array — sum-formula trick.
18. Find the Second Largest Number in an Array — single-pass logic.
19. Print Repeated Numbers in an Array — frequency counting.
20. Find Duplicate Elements in an Array — asked in almost every screening.
21. Find Common Elements Between Two Arrays — intersection logic.

OOP and language programs

22. instanceof Operator Example — runtime type checking.
23. Anonymous Class Tutorial — one-off implementations.
24. Create Your Own ArrayList — implement add/get/remove/size from scratch.
25. Program Using the Comparable Interface — natural ordering.
26. Program Using the Comparator Interface — custom ordering.
27. How to Create an Immutable Class — final fields, no setters.
28. Immutable Classes — Examples — the pattern in practice.
29. Why String is Immutable in Java — the design behind the most-asked question.

Collections programs

30. HashMap in Java with Example — the workhorse map.
31. Hashtable in Java with Example — the legacy synchronized map.
32. LinkedHashMap in Java with Example — insertion-order iteration.
33. How to Sort a HashMap — sorting by keys and values.
34. Ways to Iterate a HashMap — entrySet, keySet, forEach.
35. Fail-Fast vs Fail-Safe Iterators — with code for both.

Exception handling programs

36. Java Exception Tutorial — try/catch/finally foundations.
37. Checked Exceptions in Java — compile-time enforcement.
38. Runtime Exceptions in Java — unchecked exceptions.
39. Checked vs Unchecked Exceptions — when to use which.
40. How to Create a Custom Exception — domain-specific errors.
41. ClassNotFoundException vs NoClassDefFoundError — the confusing pair.

Serialization programs

42. What is Serialization in Java — objects to bytes.
43. Serializable vs Externalizable — control vs convenience.
44. The Externalizable Interface — custom serialization.
45. The transient Keyword with Example — excluding fields.

Concurrency programs

46. BlockingQueue Tutorial — producer-consumer foundation.
47. ArrayBlockingQueue Tutorial — bounded blocking queue.
48. LinkedBlockingQueue Tutorial — optionally-bounded queue.
49. PriorityBlockingQueue Tutorial — ordered concurrent queue.
50. SynchronousQueue Tutorial — zero-capacity handoff.

Want the full index? See the Java Programs hub and the Java Interview Prep hub.