In this tutorial, i will going to teach you how to create a program that computes factorial of a number. We all know that factorial is defined only for natural numbers and it means as the continued product of successive natural numbers from 1 to the number inputted.

Now let's start this tutorial!

1. Open JCreator or NetBeans and make a java program with a file name of factorial.java.

2. Import javax.swing package. Hence we will use a GUI (Graphical User Interface) here like the inputting the number.

1. import
   
   javax.swing.*
   
   ;
   

3. Initialize your variable in your Main, variable numInput as string and make it as an input and variable n, i, f as int. n variable will be used for parsing the numInput variable to be int, i for the loop, and variable f for the factorial of a number.

1. int
   
   n,i,f;
   
2. String
   
   numInput;
   
3. numInput =
   
   JOptionPane
   
   .showInputDialog
   
   (
   
   null
   
   , "Enter a number:"
   
   )
   
   ;
   
4. n =
   
   Integer
   
   .parseInt
   
   (
   
   numInput)
   
   ;
   

4. Make a for loop statement that the parameters have variable i will be equal to variable n, i is greater or equal than 1, and will decrement. Also, make f is equal to 1, so that we will have the formula of f=f*1 to get the factorial.

1. f =
   
   1
   
   ;
   
2. for
   
   (
   
   i=
   
   n;
   
   i>=
   
   1
   
   ;
   
   i--
   
   )
   
   {
   
3. f =
   
   f*
   
   i;
   
4. }
   

5. Lastly, display the output of the program using JOptionPane.showMessageDialog.

1. JOptionPane
   
   .showMessageDialog
   
   (
   
   null
   
   , "Factorial value is: "
   
   +
   
   f)
   
   ;
   
2. }
   

Output:



Solution:
1 x 2 x 3 x 4 x 5 = 120

Here's the full code of this tutorial:

1. import
   
   javax.swing.*
   
   ;
   
2. 
   
3. public
   
   class
   
   factorial {
   
4. 
   
5. 
   
6. public
   
   static
   
   void
   
   main(
   
   String
   
   [
   
   ]
   
   args)
   
   {
   
7. 
   
8. 
   
9. int
   
   n,i,f;
   
10. String
    
    numInput;
    
11. numInput =
    
    JOptionPane
    
    .showInputDialog
    
    (
    
    null
    
    , "Enter a number:"
    
    )
    
    ;
    
12. n =
    
    Integer
    
    .parseInt
    
    (
    
    numInput)
    
    ;
    
13. //... Computation
    
14. 
    
15. f =
    
    1
    
    ;
    
16. for
    
    (
    
    i=
    
    n;
    
    i>=
    
    1
    
    ;
    
    i--
    
    )
    
    {
    
17. f =
    
    f*
    
    i;
    
18. }
    
19. //... Output
    
20. JOptionPane
    
    .showMessageDialog
    
    (
    
    null
    
    , "Factorial value is: "
    
    +
    
    f)
    
    ;
    
21. }
    
22. 
    
23. }
    

Hope this helps! :)

Best Regards,

Engr. Lyndon R. Bermoy
IT Instructor/System Developer/Android Developer/Freelance Programmer

If you have some queries, feel free to contact the number or e-mail below.
Mobile: 09488225971
Landline: 826-9296
E-mail:[email protected]

Add and Follow me on Facebook: https://www.facebook.com/donzzsky

Visit and like my page on Facebook at: https://www.facebook.com/BermzISware

Download