check if a number is a palindrome in Java

Mathematics for Programming Numbers (Article) Numbers (Program)

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  • Understanding Palindrome Numbers: A palindrome number reads the same backward as forward. For example, 121 and 1331 are palindromes.

  • Steps to Check for Palindrome Numbers:

    • Convert the number to a string.
    • Reverse the string.
    • Compare the original string with the reversed string.

Given Input: 

12321

Expected Output: 

12321 is a palindrome.

Program:

public class PalindromeChecker {
    public static boolean isPalindrome(int number) {
        // Convert number to string
        String original = String.valueOf(number);

        // Reverse the string
        String reversed = new StringBuilder(original).reverse().toString();

        // Check if original and reversed strings are equal
        return original.equals(reversed);
    }

    public static void main(String[] args) {
        int number = 12321; // Example number to check

        if (isPalindrome(number)) {
            System.out.println(number + " is a palindrome.");
        } else {
            System.out.println(number + " is not a palindrome.");
        }
    }
}

Output:

12321 is a palindrome.

Explanation:

  • isPalindrome(int number) method checks if number is a palindrome.
  • It first converts number to a string using String.valueOf(number).
  • It uses StringBuilder to reverse the string representation of number.
  • It compares the original string (original) with the reversed string (reversed) using the equals method.
  • If they are equal, the number is a palindrome; otherwise, it's not.

Check if a Number is a Palindrome:

Steps to Check if a Number is a Palindrome:

  1. Reverse the Digits: Reverse the digits of the number.
  2. Compare: Compare the original number with the reversed number.

import java.util.Scanner;

public class PalindromeExample {
    public static void main(String[] args) {
        int n, r, sum = 0, temp;
        Scanner scanner = new Scanner(System.in);

        System.out.print("Enter the Number: ");
        n = scanner.nextInt();  // Read the input number
        temp = n;  // Store the original number

        // Reverse the number
        while (n > 0) {
            r = n % 10;  // Get the last digit
            sum = (sum * 10) + r;  // Build the reversed number
            n = n / 10;  // Remove the last digit
        }

        // Check if the original number and the reversed number are the same
        if (temp == sum) {
            System.out.println("Number is Palindrome.");
        } else {
            System.out.println("Number is not Palindrome.");
        }

        scanner.close();  // Close the scanner
    }
}
  • Scanner: Used to take input from the user.
  • Variables:
    • n: The input number.
    • r: The remainder when dividing by 10 (the last digit).
    • sum: The reversed number.
    • temp: A temporary variable to store the original number for comparison.
  • Reversing the Number:
    • In the while loop, extract the last digit of n using n % 10 and append it to sum.
    • Update n by removing the last digit (n = n / 10).
  • Comparison:
    • After the loop, compare the original number (temp) with the reversed number (sum).
    • Print the result based on the comparison.

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