Java program to find factorial of a number

In this post we will learn about Java program to find factorial of a number.

Before Witting java program let’s understand what is Factorial number?

What is Factorial Number?

In mathematics language, we can say that the factorial of a non-negative integer n, denoted by n! is the product or multiplication of all positive integers less than or equal to n.

For example, 5 ! = 5 × 4 × 3 × 2 × 1 = 120.

The factorial of a negative number doesn’t exist. And the factorial of 0 is 1

We will solve this problem statement using below 2 approaches:

Using for loop
Using recursion

Example 1:

Using for loop

Below source code of the Java Program reads number from the user and finds factorial value using for loop

package com.kkjavatutorials.client;
 
import java.util.Scanner;
/**
 * @author KK JavaTutorials
 *  This Java program is all about How to find factorial of a input number using for loop
 */
public class ClientTest1 {
 
	public static void main(String[] args) {
 
		try (Scanner scanner = new Scanner(System.in)) {
			// Take a number from keyboard using Scanner
			System.out.println("Enter a Number:");
			int number = scanner.nextInt();
			int fact = findFactorial(number);
		     System.out.println("Factorial of input " + number + " is " + fact); 
		} catch (Exception e) {
			System.out.println("Please Enter valid number..");
			e.printStackTrace();
		}
	}
	//find factorial of a number using for loop
	private static int findFactorial(int number) {
		//Validation for negative number
		if(number<0){
			throw new RuntimeException("The factorial of a negative number doesn’t exist.try With positive number");
		}
		int factorial = 1;
		for (int i = number; i >= 1; i--) {
			factorial = factorial * i;
		}
		return factorial;
	}
}

package com.kkjavatutorials.client;

import java.util.Scanner;

/**

* @author KK JavaTutorials

* This Java program is all about How to find factorial of a input number using for loop

public class ClientTest1 {

public static void main(String[] args) {

try (Scanner scanner = new Scanner(System.in)) {

// Take a number from keyboard using Scanner

System.out.println("Enter a Number:");

int number = scanner.nextInt();

int fact = findFactorial(number);

System.out.println("Factorial of input " + number + " is " + fact);

} catch (Exception e) {

System.out.println("Please Enter valid number..");

e.printStackTrace();

}

//find factorial of a number using for loop

private static int findFactorial(int number) {

//Validation for negative number

if(number<0){

throw new RuntimeException("The factorial of a negative number doesn’t exist.try With positive number");

}

int factorial = 1;

for (int i = number; i >= 1; i--) {

factorial = factorial * i;

}

return factorial;

}

Example 2:

Using recursion

Below source code of the Java Program reads number from the user and finds factorial value With using Recursion.

package com.kkjavatutorials.client;
 
import java.util.Scanner;
/**
 * @author KK JavaTutorials
 *  This Java program is all about How to find factorial of a input umber using recursion
 */
public class ClientTest2 {
 
	public static void main(String[] args) {
 
		try (Scanner scanner = new Scanner(System.in)) {
			// Take a number from keyboard using Scanner
			System.out.println("Enter a Number:");
			int number = scanner.nextInt();
			int fact = findFactorial(number);
		     System.out.println("Factorial of input " + number + " is " + fact); 
		} catch (Exception e) {
			System.out.println("Please Enter valid number..");
			e.printStackTrace();
		}
	}
 
	//find factorial of a number using recursion
	private static int findFactorial(int number) {
		//Validation for negative number
		if(number<0){
			throw new RuntimeException("The factorial of a negative number doesn’t exist.try With positive number");
		}
		//base case condition
		if (number == 1 || number == 0) {
			return 1;
		} else {
			return number * findFactorial(number - 1);
		}
	}
}

package com.kkjavatutorials.client;

import java.util.Scanner;

/**

* @author KK JavaTutorials

* This Java program is all about How to find factorial of a input umber using recursion

public class ClientTest2 {

public static void main(String[] args) {

try (Scanner scanner = new Scanner(System.in)) {

// Take a number from keyboard using Scanner

System.out.println("Enter a Number:");

int number = scanner.nextInt();

int fact = findFactorial(number);

System.out.println("Factorial of input " + number + " is " + fact);

} catch (Exception e) {

System.out.println("Please Enter valid number..");

e.printStackTrace();

}

//find factorial of a number using recursion

private static int findFactorial(int number) {

//Validation for negative number

if(number<0){

throw new RuntimeException("The factorial of a negative number doesn’t exist.try With positive number");

}

//base case condition

if (number == 1 || number == 0) {

return 1;

} else {

return number * findFactorial(number - 1);

}

I have tested both programs for few inputs as below. You may check for other input as well

Enter a Number:
4
Factorial of input 4 is 24

Enter a Number:
5
Factorial of input 5 is 12

Enter a Number:
10
Factorial of input 10 is 3628800

Enter a Number:

Factorial of input 4 is 24

Enter a Number:

Factorial of input 5 is 12

Enter a Number:

Factorial of input 10 is 3628800

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