1. Introduction

In this post, we will explore a Java program that calculates the factorial of a number using recursion. The factorial of a non-negative integer n is the product of all positive integers less than or equal to n. It is denoted by n!. For example, 5! = 5 × 4 × 3 × 2 × 1 = 120. The factorial function can be defined recursively as n! = n × (n – 1)! for n > 0 and 0! = 1.

2. Program Steps

1. Define the main class named FactorialCalculator.

2. Inside the main class, define the main method.

3. Inside the main method, define a variable num and assign the value for which we want to calculate the factorial.

4. Call the recursive factorial method, passing the num as a parameter.

5. Print the result.

3. Code Program

public class FactorialCalculator { // 1. Defining the main class

    // Defining the recursive method to calculate factorial
    static int factorial(int n) {
        if (n == 0 || n == 1) // Base case: 0! and 1! are 1
            return 1;
        else
            return n * factorial(n - 1); // Recursive call
    }

    public static void main(String[] args) { // 2. Defining the main method

        int num = 5; // 3. Assigning the number for which we want to calculate factorial
        int result = factorial(num); // 4. Calling the factorial method

        // 5. Printing the result
        System.out.println("Factorial of " + num + " is " + result);
    }
}

Output:

Factorial of 5 is 120

4. Step By Step Explanation

– Step 1: The main class FactorialCalculator is defined.

– Step 2: The main method is defined inside the main class. This is the entry point of the Java program.

– Step 3: Inside the main method, a variable num is defined and assigned the value 5, for which we want to calculate the factorial.

– Step 4: The factorial method is called with num as a parameter. This method calculates the factorial of a number using recursion. If the number is 0 or 1, the factorial is 1. For any other number n, the factorial is calculated as n * factorial(n – 1).

– Step 5: The program prints the calculated factorial of the number 5, which is 120, to the console.