Compute Factorial in Java

public class FactorialCalculator {
  
     public static void main(String[] args) {
  
         int number = 13;
         long factorial = 1;
         for(int i = 1; i <= number; ++i)
         {
         // factorial = factorial * i;
            factorial *= i;
         }
         System.out.printf("Factorial of %d = %d", number, factorial);
     }
} 

Factorial of 13 = 6227020800

• This program is used for finding the factorial of a number by using the for loop.
• A number 13 is stored into an integer variable number initially and a variable factorial is initialized as 1.
• This program functions over a for loop and loops till the variable number hence going through all numbers till 13 while multiplying these numbers one by one and consistently storing the result into the variable factorial.
• The data type long is used for storing the value in the variable factorial because the final value of the factorial is expected to be large and the data type int cannot store large values.
• Finally, the value in the variable factorial is displayed along with number as “Factorial of 13 = 6227020800”.

import java.math.BigInteger;
 
public class FactorialCalculator {
 
    public static void main(String[] args) {
 
        int number = 21;
        BigInteger factorial = BigInteger.ONE;
        for(int i = 1; i <= number; ++i)
        {
            factorial = factorial.multiply(BigInteger.valueOf(i));
        }
        System.out.printf("Factorial of %d = %d", number, factorial);
    }
}

Factorial of 21 = 51090942171709440000

• This program utilizes the BigInteger instead of the long data type for the variable factorial for storing a large value. The variable number is initialized as 21.
• The BigInteger data type can be used through the use of a Java library math.BigInteger and also a function, multiply() instead of * for calculating the factorial because “*” cannot be used next to BigInteger.
• The multiplication of the of the factorial is done by casting the number to the BigInteger and looping through all the numbers till number = 21 in the for loop.
• The multiplied values are consistently stored into the variable factorial and the result is displayed on the screen.

public class FactorialCalculator {
 
    public static void main(String[] args) {
 
        int number = 6, i = 1;
        long factorial = 1;
        while(i <= number)
        {
            factorial *= i;
            i++;
        }
        System.out.printf("Factorial of %d = %d", number, factorial);
    }
}

Factorial of 6 = 720

• This program is used for calculating the factorial of a number like the previous program but instead of the for loop, while loop is used.
• Initially, a variable number is initialized as 6, a variable i as 1 and a variable factorial as 1.
• Like the above program using for loop, this program loops and increments the variable i, number of times inside the body of the while loop and keeps multiplying its values and storing them into the variable factorial.
• Both the for loop and while loop are considered to be appropriate for performing this task however, for loop is considered a better option since it knows the number of iterations till the variable number.
• Finally, the result of the factorial of the number 6 is displayed on the screen as “Factorial of 6 = 720”.