Different ways to find the factorial of a number in Java

Different ways to find the factorial of a number in Java:

In this post, we will learn different ways to find the factorial of a number in Java. The factorial of a number is the product of all numbers starting from 1 to that number. For example, the factorail of a number n is:

1 * 2 * 3 *....* n

! is used as the factorial symbol. For example, factorial of 4 is:

4! = 1 * 2 * 3 * 4 = 24

To find the factorial of a number, we have to use a loop. This loop will find the product of all numbers starting from 1 to n.

I will show you how to do it by using a for loop, while loop, do-while loop and by using a recursive method.

Method 1: By using a for loop:

Let’s use a for loop to find the factorial:

import java.util.Scanner;

class Main {

    public static int getFactorial(int n) {
        int factorial = 1;
        for (int i = 2; i <= n; i++) {
            factorial *= i;
        }

        return factorial;
    }

    public static void main(String[] args) {
        int num;

        Scanner sc = new Scanner(System.in);
        System.out.println("Enter the number: ");
        num = sc.nextInt();

        System.out.println("The factorial of " + num + " is: " + getFactorial(num));
    }
}

Here,

num is an integer variable to store the number.
sc is a Scanner object to read the user input. It reads the input from the user and save it in the num variable.
getFactorial method is used to calculate the factorial value of a number.
- It takes a number as the argument and returns the factorial.
- The for loop runs from 2 to the given number and multiply all values to another variable.
- It returns the factorial value.

If you run this program, it will give output as like below:

Enter the number: 
12
The factorial of 12 is: 479001600

Enter the number: 
6
The factorial of 6 is: 720

Enter the number: 
5
The factorial of 5 is: 120

Method 2: By using a while loop:

We can also use a while loop to write the above program.

import java.util.Scanner;

class Main {

    public static int getFactorial(int n) {
        int factorial = 1, i = 2;
        while (i <= n) {
            factorial *= i;
            i++;
        }

        return factorial;
    }

    public static void main(String[] args) {
        int num;

        Scanner sc = new Scanner(System.in);
        System.out.println("Enter the number: ");
        num = sc.nextInt();

        System.out.println("The factorial of " + num + " is: " + getFactorial(num));
    }
}

I changed the for loop with a while loop. Both are almost similar. We are initializing the value of i before the loop starts. The loop runs until the value of i is less than or equal to n. At the end of each iteration, the value of i is incremented by 1.

If you run this program, it will give similar output.

Method 3: By using a do-while loop:

We can also use a do-while loop. The difference between while and do-while loop is that while loop verifies the condition and then runs the code block. But, do-while loop runs the code and then verifies the condition.

If I replace the while loop with a do-while loop, it will look as like below:

import java.util.Scanner;

class Main {

    public static int getFactorial(int n) {
        int factorial = 1, i = 2;
        do {
            factorial *= i;
            i++;
        } while (i <= n);

        return factorial;
    }

    public static void main(String[] args) {
        int num;

        Scanner sc = new Scanner(System.in);
        System.out.println("Enter the number: ");
        num = sc.nextInt();

        System.out.println("The factorial of " + num + " is: " + getFactorial(num));
    }
}

It will give similar output.

Method 4: Recursive way:

Instead of using a loop, we can also use a recursive function. A recursive function calls itself repeatedly to find a result. In our case, it will call recursively to find the factorial.

Below is the complete program:

import java.util.Scanner;

class Main {

    public static int getFactorial(int n, int result) {
        if (n == 1) {
            return result;
        }

        return getFactorial(n - 1, result * n);
    }

    public static void main(String[] args) {
        int num;

        Scanner sc = new Scanner(System.in);
        System.out.println("Enter the number: ");
        num = sc.nextInt();

        System.out.println("The factorial of " + num + " is: " + getFactorial(num, 1));
    }
}

For this example,

getFactorial method takes two parameters, the first one is the number and the second one is another integer value to store the result.
If the value of n is equal to 1, it returns the result value. Else, it calls the same method again and returns what it return.
On each recursive call, it decrements the value of n by 1 and multiplies the value of result by n. At one point, the value of n will be 1 and it will return the current result value.

It will give similar output:

CodeVsColor

Different ways to find the factorial of a number in Java