Question

File Factorials.java contains a program that calls the factorial method of the MathUtils class to compute the factorials of integers entered by the user.

In this program, two things can possibly occur:

• The program always returns 1 if negative integers are entered by the user. Returning 1 as the factorial of any negative integer is not correct.
• The program also returns negative numbers when the user enters integers greater than 16. Returning a negative number for values over 16 also is not correct.

To correct this problem, modify it as follows:

• Create a new exception class called NegativeArgumentException that extends IllegalArgumentException. The class has one constructor public NegativeArgumentException(String message) that takes a string as parameter.
• Create another new exception class called TooLargeArgumentException that extends IllegalArgumentException. The class has one constructor public TooLargeArgumentException(String message) that takes a string as parameter.

In the MathUtils class:

• Modify the header of the factorial method to indicate that factorial can throw NegativeArgumentException and TooLargeNumberException exceptions.
• Modify the body of factorial method to check the value of the argument and, if it is negative, throw a NegativeArgumentException with the message "Factorial is undefined for negative integers" passed as parameter to the exception constructor.
• Modify the body of factorial method to check the value of the argument and, if it is greater than 16, throw a TooLargeArgumentException with the message "Factorial is too large - overflow occurs!" passed as parameter to the exception constructor.
• Modify the main method in your Factorials class to catch the exception thrown by factorial.

// ****************************************************************
// 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.equalsIgnoreCase("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();
   }
}

// ****************************************************************
// 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;
}

}

Answer 1

Here is the completed code for this problem. Place each class in separate files as mentioned. Comments are included, go through it, learn how things work and let me know if you have any doubts or if you need anything to change. If you are satisfied with the solution, please rate the answer. If not, PLEASE let me know before you rate, I’ll help you fix whatever issues. Thanks

//NegativeArgumentException.java

public class NegativeArgumentException extends IllegalArgumentException {    

      //constructor taking a String message

      public NegativeArgumentException(String message) {

            // passing message to super class constructor

            super(message);

      }

}

//TooLargeArgumentException

public class TooLargeArgumentException extends IllegalArgumentException {

      // constructor taking a String message

      public TooLargeArgumentException(String message) {

            // passing message to super class constructor

            super(message);

      }

}

//MathUtils.java

public class MathUtils {

      // -------------------------------------------------------------

      // Returns the factorial of the argument given, throws

      // NegativeArgumentException if n is below 0, TooLargeArgumentException if n

      // is above 16

      // -------------------------------------------------------------

      public static int factorial(int n) throws NegativeArgumentException,

                  TooLargeArgumentException {

            //throwing exception if n is below 0

            if (n < 0) {

                  throw new NegativeArgumentException("Error: Negative value for n ("

                              + n + ")");

            }

            //throwing exception if n is above 16

            if (n > 16) {

                  throw new TooLargeArgumentException(

                              "Error: Too large value for n (" + n + ")");

            }

            int fac = 1;

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

                  fac *= i;

            return fac;

      }

}

//Factorials.java

import java.util.Scanner;

public class Factorials {

      public static void main(String[] args) {

            String keepGoing = "y";

            Scanner scan = new Scanner(System.in);

            while (keepGoing.equalsIgnoreCase("y")) {

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

                  int val = scan.nextInt();

                  // putting the code to find and display factorial inside try catch

                  // block

                  try {

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

                                    + MathUtils.factorial(val));

                  } catch (NegativeArgumentException e) {

                        //NegativeArgumentException has occurred

                        System.out.println(e.getMessage());

                  } catch (TooLargeArgumentException e) {

                        //TooLargeArgumentException has occurred

                        System.out.println(e.getMessage());

                  }

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

                  keepGoing = scan.next();

            }

      }

}

/*OUTPUT*/

Enter an integer: 5

Factorial(5) = 120

Another factorial? (y/n) y

Enter an integer: -2

Error: Negative value for n (-2)

Another factorial? (y/n) y

Enter an integer: 12

Factorial(12) = 479001600

Another factorial? (y/n) y

Enter an integer: 16

Factorial(16) = 2004189184

Another factorial? (y/n) y

Enter an integer: 17

Error: Too large value for n (17)

Another factorial? (y/n) n