Factorial of a number in Java

In this post i will explain how to write a program to get the factorial of a given number.I have written two programs.First one uses for loop to find the factorial and second one uses recursion.But before that i will explain how to find the factorial.
Suppose number is 4.Then to find out factorial of any given number we will multiply it with (number-1) until number becomes 1.Since the factorial of 1 is 1 So we end the procedure there.
factorial(4)=4*3*2*1
                =24
factorial(5)=5*4*3*2*1
                 =120
So in this way we can find out the factorial of any given number.

So in the following program, I am taking the input from user in main method and then called the getFactorial() function which takes the number as argument.In method getFactorial(), I have taken a local variable res  which will hold the result.Then i started a for loop in i am multiplying the number with res and after each iteration the value of i is decremented by 1.

Program Code:
package Progs;

import java.util.Scanner;

public class Factorial {

    private static int getFactorial(int number){
        int res=1;
        for(int i=number;i>=1;i--){
            res=res*i;
        }
        return res;
    }
    public static void main(String[] args) {
       
        System.out.println("Enter the number to calculate its factorial");
        Scanner sc=new Scanner(System.in);
        int number=sc.nextInt();
        int result=getFactorial(number);
        System.out.println("Factorial of given number is "+result);
    }

}

Output:
Enter the number to calculate its factorial
4
Factorial of given number is 24

Suppose number=4
for 1st iteration,
i=4       res=1
res=1* 4
     =4

for 2nd iteration,
i=3     res=4
res= 4*3
     =12

for 3rd iteration,
i=2       res=12
res=12*2
     =24

for 4th iteration,
i=1       res=4
res=24*1
     =24

for 5th iteration,
i=0   res=24
it will exit from for loop 

The following program is a recursion based program.

Program Code:
package Progs;

import java.util.Scanner;

public class Factorial_Rcursion {

    private static int getFactorial(int number) {
        int res=number;
        if(number==0)
            return 1;
        res=res*getFactorial(number-1);
        return res;
    }
    public static void main(String[] args) {
        System.out.println("Enter the number to calculate its factorial");
        Scanner sc=new Scanner(System.in);
        int number=sc.nextInt();
        int result=getFactorial(number);
        System.out.println("Factorial of given number is "+result);

    }   

}

Output:
Enter the number to calculate its factorial
5
Factorial of given number is 120

 In getFactorial()  method again i have taken a local variable which will hold the result.Then i have checked for exit condition i.e.if number==1 and after that i have written a expression which will calculate the factorial of number recursively
res=res*getFactorial(number-1);

Suppose number=4
Then
res=4*getFactorial(3)
then method will be called again until getFactorial(1) where first condition will be satisfied it will be returned to its previous call and factorial will be calculated.
res=4*3*2*getFactorial(1)
      =4*3*2*1
      =24

So in this way we can calculate the Factorial of any given number.