Java Program to Check Whether a Number is Palindrome or Not

In this program, you'll learn to check whether a number is palindrome or not in Java. This is done by using for and while loop.

Example 1: Program to Check Palindrome using while loop

public class Palindrome {

    public static void main(String[] args) {

        int num = 121, reversedInteger = 0, remainder, originalInteger;

        originalInteger = num;

        // reversed integer is stored in variable 
        while( num != 0 )
        {
            remainder = num % 10;
            reversedInteger = reversedInteger * 10 + remainder;
            num  /= 10;
        }

        // palindrome if orignalInteger and reversedInteger are equal
        if (originalInteger == reversedInteger)
            System.out.println(originalInteger + " is a palindrome.");
        else
            System.out.println(originalInteger + " is not a palindrome.");
    }
}

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:

Palindrome execution steps
num num != 0 remainder reversedInteger
121 true 1 0 * 10 + 1 = 1
12 true 2 1 * 10 + 2 = 12
1 true 1 12 * 10 + 1 = 121
0 false - 121

Example 2: Program to Check Palindrome using for loop

public class Palindrome {

    public static void main(String[] args) {

        int num = 11221, reversedInteger = 0, remainder, originalInteger;

        originalInteger = num;

        // reversed integer is stored in variable
        for( ;num != 0; num /= 10 )
        {
            remainder = num % 10;
            reversedInteger = reversedInteger * 10 + remainder;
        }

        // palindrome if orignalInteger and reversedInteger are equal
        if (originalInteger == reversedInteger)
            System.out.println(originalInteger + " is a palindrome.");
        else
            System.out.println(originalInteger + " is not a palindrome.");
    }
}

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.