//package numeric;
/**
* This class calculates the Factorial of a
* numbers passed into the program through
* command line arguments.
*
* @author Alex Laird
* @version 1.0
* File: Factorial.java
* Created: Sep 2008
*/
public class Factorial
{
/**
* Returns the Factorial of a number that
* is passed into the method through command
* line arguments.
*
* @param a The counting variable and initial condition for the Factorial.
* @param factorial The running value of the Factorial.
* @throws NegativeNumberException if the input given is negative.
* @returns the calculated Factorial.
*/
public static double calcFactorial(int a) throws Exception
{
double factorial = a;
// throw an exception if the input is negative
if(a < 0)
{
throw new Exception("The user has entered a "
+ "negative number.");
}
for(int i = (a - 1); i > 1; i--)
factorial *= i;
return factorial;
}
/**
* The main method from which the program executes;
* it handles all I/O and method execution.
*
* @param args Arguments received from the command line (one number).
* @param factorial The calculated Factorial of args[0].
*/
public static void main(String[] args)
{
// ensure the user only enters one argument
if(args.length == 1)
{
// ensure the users argument is a number
try
{
// calculate factorial
double factorial = calcFactorial(Integer.parseInt(args[0]));
System.out.println("The Factorial of " + args[0] + " is "
+ factorial + ".");
}
catch(NumberFormatException c)
{
System.out.println("Your argument must be in "
+ "the form of an integer when "
+ "running the program (ex. "
+ "enter 'java numeric."
+ "Factorial 5').");
}
catch(Exception c)
{
// used only in GUI
}
}
else
{
System.out.println("Enter one number as an argument "
+ "when running the program (ex. "
+ "enter 'java numeric.Factorial 5').");
}
}
}