Programming Example

check if a number is a palindrome in Java

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Information & Algorithm

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:

Expected Output:

12321 is a palindrome.

Program Code

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:

Reverse the Digits: Reverse the digits of the number.
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.

How to learn from this program

First read the algorithm, then study the program code line by line. After that, compare the code with the output and finally go through the explanation. This approach helps learners understand both the logic and the implementation properly.

Practice suggestion

After understanding this example, try to rewrite the same program without looking at the code. Then change some values or logic and run it again. This helps improve confidence and keeps learners engaged on the page for longer.