Java Factorial Program

This topic demonstrates how to find factorial of a given number using different techniques in java.

---

What is Factorial?

Factorial is a multiplication from given number to 1.

Suppose given number is 5 then, we multiply 5 with all previous numbers upto 1 as.

5 * 4 * 3 * 2 * 1 = 120

Factorial is denoted by ! (Exclamation Marks)

Example

Finding factorial of 5 using program

---

Different ways of finding factorial

For iterating the multiple times we have different looping techniques. We can use any of the following loop to find the factorial

• Using for loop
• Using while loop
• Using do while loop
• Using recursion

1. Factorial using for loop

In below example we are using a scanner class to get input from user.

import java.util.Scanner;
public class FactorialEx 
{
	public static void main(String[] args) 
	{
		int i,num,result=1;
		Scanner sc = new Scanner(System.in);
		System.out.print("Enter number : ");
		num = sc.nextInt();
		
		for(i=num;i>=1;i--)
		{
			result = result * i;
		}
		System.out.print("Factorial of "+num+" is "+result);
	}
}

Output

In above example, we have started our loop from given number 5. Inside the loop we have written one statement to multiply the current interation number with previous result. The loop will continue till we get 1 in the iteration.

---

2. Factorial using While Loop

import java.util.Scanner;
public class FactorialEx 
{
	public static void main(String[] args) 
	{
		int num,num2,result=1;
		Scanner sc = new Scanner(System.in);
		System.out.print("Enter number : ");
		num = sc.nextInt();
		num2=num;
		while(num>=1)
		{
			result = result * num;
			num--;
		}
		System.out.print("Factorial of "+num2+" is "+result);
	}
}

Output

In above example, the loop checks for the condition wheather num reaches to 1 or not. if not then result is generated by multiplying the current number and then number is decremented by 1.

---

3. Factorial using Do While Loop

It is similar to the while loop, but the difference is do while loop executes at least once.

import java.util.Scanner;
public class FactorialEx 
{
	public static void main(String[] args) 
	{
		int num,num2,result=1;
		Scanner sc = new Scanner(System.in);
		System.out.print("Enter number : ");
		num = sc.nextInt();
		num2=num;
		do
		{
			result = result * num;
			num --;
		}while(num>=1);
		System.out.print("Factorial of "+num2+" is "+result);
	}
}

Output

Above program is similar to the while loop but, Only the do keyword is used before the while loop and body is written for do keyword instead of while.

---

4. Factorial using Recursion

Recursion is the process where the function calls itself again and again just like loops.

import java.util.Scanner;
public class FactorialEx 
{
	int fact(int f)
	{
		int getnum=f;
		if(f==0)
			return 1;
		else
		{
			getnum = getnum * fact(f-1);
			return getnum;
		}
	}
	public static void main(String[] args) 
	{
		Scanner sc = new Scanner(System.in);
		FactorialEx f = new FactorialEx();
		int num=0;
		
		System.out.print("Enter Number to find factorial : ");
		num = sc.nextInt();
		System.out.println("Factorial of "+num+" is "+f.fact(num));
	}
}

Output