Before beginning to write code, you should know what these numbers are. So, let's start with a little introduction into these numbers.
Armstrong Number
A number is called an Armstrong number if the sum of its digits to the power of the number of digits is the number itself. For example,
we have a number, 1634. To determine whether 1634 is an Armstrong, we need to check:
Does 1^4 + 6^4 + 3^4 + 4^4 equal 1634 ?
Yes! So 1634 is Armstrong Number.
Similarly, 153 is Armstrong because 1^3 + 5^3 + 3^3 equals to 153.
Palindrome Number
A number is said to be a Palindrome if the reverse of its digit is number itself. For eg. 121, 959, 1441, etc.
Prime Number
A natural number greater than 1 is called a prime number, if it has no divisor other than 1 and itself. For eg. 2, 3, 5, 7, ...
The Java program written below has a class named VariousNumbers which contain three public static functions excluding main, listed below:
  1. public static boolean Armstrong(int) // Return true, if an integer is found to be an Armstrong, else return false.
  2. public static boolean Palindrome(int) // Return true, if an integer is found to be a Palindrome, else return false.
  3. public static boolean Prime(int) // Return true, if an integer is found to be a Prime, else return false.
Code
  1. public class VariousNumbers {
  2. public static void main(String[] args) {
  3. System.out.println("Armstrong Numbers 1 to 10000 >>");
  4. for (int i = 1; i <= 10000; i++) {
  5. if (Armstrong(i) == true) {
  6. System.out.print(i + " ");
  7. }
  8. }
  9. System.out.println("\nPalindrome Numbers 100 to 300 >>");
  10. for (int i = 100; i <= 300; i++) {
  11. if (Palindrome(i) == true) {
  12. System.out.print(i + " ");
  13. }
  14. }
  15. System.out.println("\nPrime Numbers up to 100 >>");
  16. for (int i = 1; i <= 100; i++) {
  17. if (Prime(i) == true) {
  18. System.out.print(i + " ");
  19. }
  20. }
  21. }
  22. public static boolean Armstrong(int num) {
  23. int num1 = num;
  24. /* Converting Integer to String. It'll help to find number of
  25. digits in the Integer by using length() */
  26. String str = Integer.toString(num);
  27. int rem;
  28. int result = 0;
  29. while (num > 0) {
  30. rem = num % 10;
  31. num = num / 10;
  32. result = result + ((int) Math.pow(rem, str.length()));
  33. }
  34. if (result == num1) {
  35. return true;
  36. } else {
  37. return false;
  38. }
  39. }
  40. public static boolean Palindrome(int num) {
  41. int num1 = num;
  42. int rem;
  43. int result = 0;
  44. while (num > 0) {
  45. rem = num % 10;
  46. num = num / 10;
  47. result = (result + rem) * 10;
  48. }
  49. result /= 10;
  50. if (result == num1) {
  51. return true;
  52. } else {
  53. return false;
  54. }
  55. }
  56. public static boolean Prime(int num) {
  57. if (num < 2) {
  58. return false;
  59. }
  60. int div = num / 2;
  61. for (int i = 2; i <= div; i++) {
  62. if (num % i == 0) {
  63. return false;
  64. }
  65. }
  66. return true;
  67. }
  68. }
Output
Armstrong Numbers 1 to 10000 >>
1 2 3 4 5 6 7 8 9 153 370 371 407 1634 8208 9474
Palindrome Numbers 100 to 300 >>
101 111 121 131 141 151 161 171 181 191 202 212 222 232 242 252 262 272 282 292
Prime Numbers up to 100 >>
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97