Find the Factorial of a Number in Java

In this article, we will find the Factorial of a Number in Java using 4 methods: For loop, While loop, Recursion, and BigInteger.

Factorial of a Number

The Factorial of a positive integer is the multiplication of all positive integers smaller than or equal to n. For example factorial of 6 is 6 x 5 x 4 x 3 x 2 x 1 = 720.

Algorithm:

Step 1: Start

Step 2: Read the number n

Step 3: [Initialize]

i=1, fact=1

Step 4: Repeat step 4 through 6 until i=n

Step 5: fact=fact*i

Step 6: i=i+1

Step 7: Print the fact

Step 8: Stop

Method 1: Using For loop

Code:

class FactorialExample
{  
 public static void main(String args[])
 {  
  int i,fact=1;  
  int number = 7; //It is the number to calculate factorial    
  for(i=1;i<=number;i++)
  {    
      fact=fact*i;    
  }    
  System.out.println("Factorial of "+number+" is: "+fact);    
 }  
}

Output:

Method 2: Using while loop

Code:

public class Factorial {

    public static void main(String[] args) {

        int num = 8, i = 1;
        long factorial = 1;
        while(i <= num)
        {
            factorial *= i;
            i++;
        }
        System.out.printf("Factorial of %d = %d", num, factorial);
    }
}

Output:

Method 3: Using Recursion

Code:

class FactorialExample2
{  
 static int factorial(int n)
 {    
  if (n == 0)    
    return 1;    
  else    
    return(n * factorial(n-1));    
 }    
 
 public static void main(String args[])
 {  
  int i,fact=1;  
  int number = 5;//It is the number to calculate factorial    
  fact = factorial(number);   
  System.out.println("Factorial of "+number+" is: "+fact);    
 }  
}

Output:

Method 4: Using BigInteger

Code:

import java.math.BigInteger;

public class Factorial {

    public static void main(String[] args) {

        int num = 25;
        BigInteger factorial = BigInteger.ONE;
        for(int i = 1; i <= num; ++i)
        {
            // factorial = factorial * i;
            factorial = factorial.multiply(BigInteger.valueOf(i));
        }
        System.out.printf("Factorial of %d = %d", num, factorial);
    }
}

Output: