Factorial Calculator in Java: Loops and Recursion

Java Project - Factorial Calculation:

Factorial Calculator:

Calculate the factorial of a number using loops or recursion.

This project calculates the factorial of a given number using either loops or recursion. The factorial of a number is the product of all positive integers up to that number.

Input: A number.
Output: Factorial of the number.

Example:

• Input: 5
• Output: 120

Solution 1: Factorial Calculation using Loops

Code:

import java.util.Scanner;

public class FactorialUsingLoop {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        
        // Taking user input
        System.out.print("Enter a number: ");
        int num = scanner.nextInt();
        
        // Initializing factorial value to 1
        int factorial = 1;
        
        // Loop to calculate factorial
        for (int i = 1; i <= num; i++) {
            factorial *= i;
        }
        
        // Displaying the result
        System.out.println("Factorial of " + num + " is: " + factorial);
        
        scanner.close(); // Closing the scanner resource
    }
}

Output:

Enter a number:  6
Factorial of 6 is: 720

Explanation :

• Input and Scanner: The program takes an integer input from the user.
• Factorial Initialization: A variable factorial is initialized to 1 to store the result.
• For Loop: The loop runs from 1 to the input number, multiplying the factorial variable by each value of the loop counter.
• Display Result: After the loop ends, the factorial result is displayed to the user.
• Close Scanner: The scanner is closed to free up system resources.

Solution 2: Using a For Loop with Guess Limits

Code:

import java.util.Scanner;

public class FactorialUsingRecursion {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        
        // Taking user input
        System.out.print("Enter a number: ");
        int num = scanner.nextInt();
        
        // Calling recursive function to calculate factorial
        int result = calculateFactorial(num);
        
        // Displaying the result
        System.out.println("Factorial of " + num + " is: " + result);
        
        scanner.close(); // Closing the scanner resource
    }
    
    // Recursive function to calculate factorial
    public static int calculateFactorial(int n) {
        if (n == 0 || n == 1) { // Base case: factorial of 0 or 1 is 1
            return 1;
        } else {
            return n * calculateFactorial(n - 1); // Recursive call
        }
    }
}  

Output:

Enter a number:  7
Factorial of 7 is: 5040

Explanation:

• Input and Scanner: The program takes an integer input from the user.
• Recursive Function: The calculateFactorial() method is a recursive function that calls itself until the base case (n == 0 or n == 1) is reached.
• Base Case: The factorial of 0 or 1 is returned as 1.
• Recursive Call: For other values of n, the function multiplies n by the factorial of n-1.
• Display Result: After the recursive function completes, the result is displayed to the user.
• Close Scanner: The scanner is closed to free up system resources.