// **************************************************************** // Factorial
ID: 3819452 • Letter: #
Question
// ****************************************************************
// 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();
}
}
}
// ****************************************************************
// 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;
}
}
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. 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. Returning l 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 mustreturn a value, and even if it prints an emor 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. You could define your own exception class, but there is already an exception appropriate for this situatio IllegalArgumentException, which extends RuntimeException. Modify your n program as follows Modify the header of the factorial method to indicate that factorial can throw an IllegalArgumentException since factorial itself does not have the try and catch. Modify the body of factorial to check the value of the argument and, if it is negative, throw an IllegalArgumentException. Note that what you pass to throw is actually an instance of the IllegalArgumentException class, and that the constructor takes a String parameter. Use this parameter to be specific about what the problem is 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. 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 2. 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 canalso be thought ofas an IllegalArgumentException 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 an IllegalArgumentException in either case, but pass different messages to the constructor so that the problem is clear.Explanation / Answer
import java.util.Scanner;
/**
*
* @author Sam
*/
// ****************************************************************
// Factorials.java
//
// Reads integers from the user and prints the factorial of each.
//
// ****************************************************************
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();
try { //try block within while loop to ensure that the while loop is not terminated when exception is thrown
System.out.println("Factorial(" + val + ") = "
+ MathUtils.factorial(val));
} catch (IllegalArgumentException e) { //same catch will catch both the exception given in the specs (q1 and q2)
System.err.println(e.getMessage());
}
System.out.print("Another factorial? (y/n) ");
keepGoing = scan.next();
}
}
}
// ****************************************************************
// MathUtils.java
//
// Provides static mathematical utility functions.
//
// ****************************************************************
class MathUtils {
//-------------------------------------------------------------
// Returns the factorial of the argument given
//-------------------------------------------------------------
public static int factorial(int n) throws IllegalArgumentException{
if (n<0)
throw new IllegalArgumentException("Factorial of -ve number cannot be calculated"); //this is accordinfg to question 1
if (n>16)
throw new IllegalArgumentException("Argument too large to be calculated."); //this is accordinfg to question 2
int fac = 1;
for (int i = n; i > 0; i--) {
fac *= i;
}
return fac;
}
}
Hello champ. I tried my best to make minimum changes to meet your need. You can find the changes easily as the updated section of the code are made bold. To make things easier, I have also commented the lines where changes were made. I hope you will the code and please let me know if you face any difficulty with the code.
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