Factorial Program Using Loop And Recursion in java

Factorial program in Java using recursion

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

You can also check : Factorial program in java using Iterative method.

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.

Factorial program in Java using recursion
Factorial program in Java using recursion

Our logic of Factorial program using recursion

• Our program will take an integer input from the user which should be a whole number.
• If the number input is negative then print ‘The factorial can’t be calculated’.
• 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.

java program to calculate Factorial using recursion

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 1

Enter a whole number to find Factorial 
5
Factorial = 120

Explanation

calculate factorial in java using recursion

Output 2

Enter a whole number to find Factorial 
6
Factorial = 720

Explanation

Program Explanation

  1. Imports: The program imports all utilities from the java.util package.
  2. Class Definition: It defines a public class named Main.
  3. Recursive Function: It contains a static method fact that calculates the factorial of a number using recursion. If the input is 0, it returns 1. Otherwise, it returns num multiplied by the factorial of num-1.
  4. Main Method: This is where execution starts. It reads a number from the user using a Scanner object, then calls the fact method with this number and prints the result, which is the factorial of the number.
  5. Input and Output: The program prompts the user to enter a whole number, calculates its factorial, and prints the result.