1. Integer - неизменяемый.
2.
https://stackoverflow.com/a/40523
import java.util.Scanner;
public class Main {
private static Integer invertDigits(Integer number) {
Integer temp = 0;
while (number != 0) {
temp = temp * 10 + number % 10;
number /= 10;
}
return temp;
}
public static void main(String[] args) throws Exception {
Scanner scanner = new Scanner(System.in);
Integer number;
System.out.print("Enter number: ");
number = scanner.nextInt();
System.out.println("Reverse digit order: " + invertDigits(number));
}
}