How can I swap the first and last digits of a number in Java using for for-loops?

Question

This is my code (which is not working) without using loops.

System.out.println("Enter a five digit number: ");
int number = scanner.nextInt();

int lastDigit = number % 10;            //by using the % operator, we are able to retrieve the last digit of the number

int firstDigit = number;
while(firstDigit > 9) {
    firstDigit /= 10;
}
//======================================================//
System.out.println("The first digit of the number is " + firstDigit);
System.out.println("The last digit of the number is " + lastDigit);

String string = Integer.toString(number);

char first = string.charAt(0);
char last = string.charAt(string.length() - 1);

string.replace(first, last);
string.replace(last, first);

System.out.println(string);

Answer 1

A method to swap the digits using for loop:

static int swapDigits(int x) {
    System.out.print(x + " -> ");
    int sign = Integer.signum(x);
    x *= sign;  // invert negative number if necessary

    int last = x % 10;
    int n = x / 10;
    int s = 0;       // sum for the digits in the middle
    for (int p = 1; n > 10; n /= 10, last *= 10, p *= 10) {
        s += p * (n % 10);
    }
    return sign * (10 * (last + s) + n); // restore the sign and get swapped digits
}

Tests:

System.out.println(swapDigits(12345));  // 12345 -> 52341
System.out.println(swapDigits(607081)); // 607081 -> 107086
System.out.println(swapDigits(98760));  // 98760 -> 8769  // leading 0 lost
System.out.println(swapDigits(-12345)); // -12345 -> -52341