Factorial program in Java using recursion

In this tutorial we are going to learn writing java program to calculate the Factorial of a given number using recursion.

What is Recursion?

Recursion is a method that defines something in terms of itself, which means it is a process in which a function calls itself again and again till condition satisfy.

A complete function can be split down into various sub-parts in recursion. It makes code look simple and compact. It is also defined as the process of defining a program or problem in terms of itself. Let’s have a look at the simple diagram that explains the working of recursion.

Our logic of Factorial program using recursion

1. Our program will take an integer input from the user which should be a whole number.
2. If the number input is negative then print ‘The factorial can’t be calculated’.
3. Then use fact(num) user-defined recursive function that will return the factorial of the given number.

Let’s understand through a diagram how our recursive function will work on input 7.

Algorithm to calculate factorial using recursion

Step 1: Start
Step 2: Create a user-define function ‘fact(num)’ which take an integer as an parameter and return num*fact(num-1).
Step 3: Create a variable num.
Step 4: Take an integer input from the user and store it into num variable.
Step 5: Pass the variable num as the parameter of user-defined function ‘func’ and print the result returned by the function.
Step 6: Stop

Java Program to calculate factorial using recursion

import java.util.*;

public class Main {
    
	static long fact(long num){
        if (num == 0){
            return 1;
        } else {
            return(num * fact(num-1));
        }
    }
    
    public static void main(String[] args) {
        long num;
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter a whole number to find Factorial ");
        num= sc.nextInt();
        System.out.println("Factorial = "+fact(num));
    }
}

Output:

Enter a whole number to find Factorial 
5
Factorial = 120

Explanation