Mastering Java Factorial: A Comprehensive Guide to Efficiently Find Factorials

What is factorial?

    Factorial simply means multiplying all the whole numbers down to 1. For example, let's select 5. If you want to find out the factorial of 5 (also denoted as 5!), just multiply it with all the whole numbers below it until you reach 1.
5! = 5 x 4 x 3 x 2 x 1
5! = 120 (answer)

Understanding the flow

    Now that we understand what factorial is, how can we implement this logic into our code? We can do this step by step. First, we select a random whole number, in this case, 5. Then we decrement 5 by 1, which is 4, and multiply it by 5. Now we have a summation of 20. Next, we decrement 4 by 1, which is 3, and multiply our summation of 20 by 3. This gives us a summation of 60. We still haven't reached 1 yet, so we have to do it again. We decrement 3 by 1, which is 2, and multiply it by 60, resulting in a summation of 120. Now, we have reached 1. Here we have to stop.

Factorial using for-loop

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import java.util.Scanner;

public class Factorial {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
int factorial;
System.out.println("Enter a whole number : ");
factorial = scanner.nextInt(); // user input
/*
initial value = factorial
in the following for-loop we are
decrementing values by 1 in each step
*/
for (int i = factorial - 1; i >= 1; i--) {
System.out.println("Multiplying " + factorial + " by " + i);
factorial = factorial * i;
System.out.println("Summation: " + factorial);
}
//We got the answer
System.out.println("Factorial : " + factorial); // final answer
}
}

Output:

Enter a whole number : 

5

Multiplying 5 by 4

Summation: 20

Multiplying 20 by 3

Summation: 60

Multiplying 60 by 2

Summation: 120

Multiplying 120 by 1

Summation: 120

Factorial : 120

Factorial using recursion

import java.util.Scanner;

public class FactorialUsingRecursion {
static int factorial;

public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
System.out.println("Enter no. : ");
factorial = scanner.nextInt();
factorial = factorial(factorial);
System.out.println("Factorial : " + factorial);
}

static int factorial(int counter) {
    if (counter >1) {
       counter--;
factorial = factorial * counter; return factorial(counter); } else {

         return factorial;

    }
    }
}

Output:

Enter no. : 9

Factorial : 362880

    Hope you liked this blog. If you still have any doubts please let me know in the comment section. Happy coding!