Question

Throwing Exceptions - JAVA

File Factorials contains a program that calls the factorial method of theMathUtils class to compute the factorials of integers entered by the user. Save these files to your directory and study the code in both, then compile and run Factorials to see how it works. Try several positive integers, then try a negative number. You should find that it works for small positive integers (values < 17), but that it returns a large negative value for larger integers and that it always returns 1 for negative integers.

1. Create a custom exception class called myException. This class should take in one String parameter that can be passed to the super class inside the constructor
2. Returning 1 as the factorial of any negative integer is not correct—mathematically, the factorial function is not defined for negative integers. To correct this, you could modify your factorial method to check if the argument is negative, but then what? The method must return a value, and even if it prints an error message, whatever value is returned could be misconstrued. Instead it should throw an exception indicating that something went wrong so it could not complete its calculation. Use your myException class to handle the situation. Modify your program as follows:
   1. Modify the header of the factorial method to indicate that factorial can throw a myException.
   2. Modify the body of factorial to check the value of the argument and, if it is negative, throw a myException. Note that what you pass to throw is actually an instance of the myException class, and that the constructor takes a String parameter. Use this parameter to be specific about what the problem is.
   3. Compile and run your Factorials program after making these changes. Now when you enter a negative number an exception will be thrown, terminating the program. The program ends because the exception is not caught, so it is thrown by the main method, causing a runtime error.
   4. Modify the main method in your Factorials class to catch the exception thrown by factorial and print an appropriate message, but then continue with the loop. Think carefully about where you will need to put the try and catch.
3. Returning a negative number for values over 16 also is not correct. The problem is arithmetic overflow—the factorial is bigger than can be represented by an int. This can also be thought of as a myException — this factorial method is only defined for arguments up to 16. Modify your code in factorial to check for an argument over 16 as well as for a negative argument. You should throw a myException in either case, but pass different messages to the constructor so that the problem is clear.

Submit the following:

Modified MathUtils.java

Modified Factorials.java

myException.java

// ****************************************************************
// MathUtils.java
//
// Provides static mathematical utility functions.
//
// ****************************************************************
public class MathUtils
{
   //-------------------------------------------------------------
   // Returns the factorial of the argument given
   //-------------------------------------------------------------
   public static int factorial(int n)
   {
       int fac = 1;
       for (int i=n; i>0; i--)
           fac *= i;
       return fac;
   }
}

// ****************************************************************
// Factorials.java
//
// Reads integers from the user and prints the factorial of each.
//
// ****************************************************************
import java.util.Scanner;
public class Factorials
{
   public static void main(String[] args)
   {
       String keepGoing = "y";
       Scanner scan = new Scanner(System.in);
       while (keepGoing.equals("y") || keepGoing.equals("Y"))
       {
           System.out.print("Enter an integer: ");
           int val = scan.nextInt();
           System.out.println("Factorial(" + val + ") = "
                   + MathUtils.factorial(val));
           System.out.print("Another factorial? (y/n) ");
           keepGoing = scan.next();
       }
   }
}

Answer 1

class GFG {

     

    // This function finds factorial of

    // large numbers and prints them

    static void factorial(int n)

    {

        int res[] = new int[500];

        // Initialize result

        res[0] = 1;

        int res_size = 1;

        // Apply simple factorial formula

        // n! = 1 * 2 * 3 * 4...*n

        for (int x = 2; x <= n; x++)

            res_size = multiply(x, res, res_size);

        System.out.println("Factorial of given number is ");

        for (int i = res_size - 1; i >= 0; i--)

            System.out.print(res[i]);

    }

     

    // This function multiplies x with the number

    // represented by res[]. res_size is size of res[] or

    // number of digits in the number represented by res[].

    // This function uses simple school mathematics for

    // multiplication. This function may value of res_size

    // and returns the new value of res_size

    static int multiply(int x, int res[], int res_size)

    {

        int carry = 0; // Initialize carry

        // One by one multiply n with individual

        // digits of res[]

        for (int i = 0; i < res_size; i++)

        {

            int prod = res[i] * x + carry;

            res[i] = prod % 10; // Store last digit of

                                // 'prod' in res[]

            carry = prod/10; // Put rest in carry

        }

        // Put carry in res and increase result size

        while (carry!=0)

        {

            res[res_size] = carry % 10;

            carry = carry / 10;

            res_size++;

        }

        return res_size;

    }

    // Driver program

    public static void main(String args[])

    {

        factorial(100);

    }

}

import java.util.Scanner;

import javax.swing.JOptionPane;

public class App {

public static void main(String[] args) {

    int value;

   //E.g. 4!=4*3*2*1

    Scanner keyboard=new Scanner(System.in);

    System.out.println("Enter a value for factorial");

    value=keyboard.nextInt();

    try{

    System.out.println(calculate(value));}catch(NumberFormatException e){

        System.out.println("invalid error. No negative numbers");

    }

}

private static int calculate(int value){

    if(value==1 || value==0){

        return 1;

    }

    return calculate(value-1)*value;

}

}

-----------------------------------------------------------------------------------------

import java.util.Scanner;

public class Factorials

{

public static void main(String[] args)

{

String keepGoing = "y";

Scanner scan = new Scanner(System.in);

while (keepGoing.equals("y") || keepGoing.equals("Y"))

{

System.out.print("Enter an integer: ");

int val = scan.nextInt();

System.out.println("Factorial(" + val + ") = "

+ MathUtils.factorial(val));

System.out.print("Another factorial? (y/n) ");

keepGoing = scan.next();

}

}

}

public class MathUtils

{

public static int factorial(int n)

{

int fac = 1;

for (int i=n; i>0; i--)

fac *= i;

return fac;

}

}