Четвертая лаба Java

package com.company;


import java.math.BigInteger;
import java.util.InputMismatchException;
import java.util.Scanner;

public class Main
{

    public static void main(String[] args)
    {

        int num = 0;

        Scanner in = new Scanner(System.in);

        System.out.print("Please, enter a number for factorial: ");

        try
        {
           num = in.nextInt();
        }
        catch (InputMismatchException ex)
        {
            System.err.println("Error, you should enter a digit");
            System.exit(1);

        }

        try
        {
          System.out.println("factorial("+ num +") = " +factorial(BigInteger.valueOf(num)));
        }
        catch (IllegalArgumentException ex)
        {
            System.err.println(ex.getMessage());
            System.exit(2);
        }

        System.out.print("Please, enter a number for fibonachi: ");

        try
        {
            num = in.nextInt();
        }
        catch (InputMismatchException ex)
        {
            System.err.println("Error, you should enter a digit");
            System.exit(1);
        }

        try
        {
            System.out.println("fibonachi №"+ num +" = " +fibonachi(num));
        }
        catch (IllegalArgumentException ex)
        {
            System.err.println(ex.getMessage());
            System.exit(3);
        }

    }

    public  static BigInteger factorial (BigInteger n)
    {
        if (n.compareTo(BigInteger.valueOf(0)) == -1)  throw new IllegalArgumentException("Error, number should be positive");
        return ((n.compareTo(BigInteger.valueOf(0)) == 0)||(n.compareTo(BigInteger.valueOf(1))==0)) ? BigInteger.valueOf(1) : n.multiply(factorial( n.add(BigInteger.valueOf(-1))));
    }



    public static BigInteger fibonachi(int n)
    {
        if(n < 0) throw new IllegalArgumentException("Error, number should be positive");

        BigInteger a = BigInteger.valueOf(0);
        BigInteger b = BigInteger.valueOf(1);

        while (n--!=0)
        {
            BigInteger temp = b;
            b=a.add(b);
            a=temp;
        }
        return a;
    }

}