Example 1: Program to Check Palindrome using while loop

1. public class Palindrome {
3. public static void main(String[] args) {
5. int num = 121, reversedInteger = 0, remainder, originalInteger;
7. originalInteger = num;
9. // reversed integer is stored in variable
10. while( num != 0 )
11. {
12. remainder = num % 10;
13. reversedInteger = reversedInteger * 10 + remainder;
14. num /= 10;
15. }
17. // palindrome if orignalInteger and reversedInteger are equal
18. if (originalInteger == reversedInteger)
19. System.out.println(originalInteger + " is a palindrome.");
20. else
21. System.out.println(originalInteger + " is not a palindrome.");
22. }
23. }

When you run the program, the output will be:

121 is a palindrome number.

In this program,

• First, given number (num)’s value is stored in another integer variable, originalInteger. This is because, we need to compare the values of reversed number and original number at the end.
• Then, a while loop is used to loop through num until it is equal to 0.
  • On each iteration, the last digit of num is stored in remainder.
  • Then, remainder is added to reversedInteger such that it is added to the next place value (multiplication by 10).
  • Then, the last digit is removed from num after division by 10.
• Finally, reversedInteger and originalInteger are compared. If equal, it is a palindrome number. If not, it isn’t.

Here are the execution steps that takes place:

Example 2: Program to Check Palindrome using for loop

1. public class Palindrome {
3. public static void main(String[] args) {
5. int num = 11221, reversedInteger = 0, remainder, originalInteger;
7. originalInteger = num;
9. // reversed integer is stored in variable
10. for( ;num != 0; num /= 10 )
11. {
12. remainder = num % 10;
13. reversedInteger = reversedInteger * 10 + remainder;
14. }
16. // palindrome if orignalInteger and reversedInteger are equal
17. if (originalInteger == reversedInteger)
18. System.out.println(originalInteger + " is a palindrome.");
19. else
20. System.out.println(originalInteger + " is not a palindrome.");
21. }
22. }

When you run the program, the output will be:

11221 is not a palindrome.

In the above program, for loop is used instead of a while loop.

On each iteration, num /= 10 is executed and condition num !=0 is checked.