Palindrome number and string

A palindrome is a word that has the same meaning when read backwards as when read from the front. Examples of palindromes are: Anna, madam, level, racecar and many more.
Mathematics also knows palindromes. Here we talk about palindromes if the numbers do not change when the sequence of numbers is reversed, for example 22 or 141.

Check Palindrome number

The code checks if a number is a palindrome number or not.

A palindrome number is a number which remains the same when its digits are reversed.

Here’s how the code works:

1. The Scanner class is used to get an input from the user, which is the number to be checked for palindromicity.
2. The variable temp is initialized with the input number, which is later used for comparison with the reversed number.
3. In the while loop, the number is being reversed.
   • The remainder of the number after dividing by 10 is stored in the variable r.
   • The reversed number is then calculated by multiplying the previous value of rev by 10 and adding the value of r to it.
   • Finally, the value of x is updated by dividing it by 10.
4. After the while loop, the value of temp is compared with rev to determine if the number is a palindrome or not.
   • If they are equal, the number is a palindrome, and a message is printed indicating the same.
   • If they are not equal, the number is not a palindrome, and a message indicating the same is printed.
5. The scan.close() method is used to close the scanner object.

import java.util.Scanner;

public class PalindromeNumber {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int x, temp, r, rev = 0;
        System.out.println("Enter number to check palindrome or not: ");
        x = scan.nextInt();
        temp = x;

        scan.close();

        while (x != 0) {
            r = x % 10;
            rev = rev * 10 + r;
            x = x / 10;
        }

        if (temp == rev) {
            System.out.println(temp + " is palindrome number");
        } else {
            System.out.println(temp + " is not palindrome number");
        }
    }
}

Output

Enter number to check palindrome or not: 262
262 is palindrome number

Enter number to check palindrome or not: 13
13 is not palindrome number

Check Palindrome number or string

This Java program checks if a string is a palindrome or not.

1. It takes a string input from the user using the Scanner class.
2. It initializes a variable reverse as an empty string and then uses a for loop to reverse the string. The loop iterates over the string starting from the last character, and concatenates each character to the reverse string.
3. After the loop, it compares the original string with the reversed string using the equals method. If the two strings are equal, it means the original string is a palindrome, and the program prints a message saying so.
4. If the two strings are not equal, the program prints a message saying that the string is not a palindrome.
5. Finally, the Scanner object is closed to release the resources.

import java.util.Scanner;

public class PalindromeString {
    public static void main(String[] args) {
        String str, reverse = "";
        Scanner scan = new Scanner(System.in);

        System.out.println("Enter a string or number to check palindrome number: ");
        str = scan.nextLine();
        int length = str.length();

        scan.close();

        for (int i = length - 1; i >= 0; i--) {
            reverse = reverse + str.charAt(i);
        }

        if (str.equals(reverse)) {
            System.out.println(str + " is a palindrome.");
        } else {
            System.out.println(str + "isn't a palindrome.");
        }
    }
}

Output

Enter a string or number to check palindrome number: 
madam
madam is a palindrome.