Factorial of a number Program in Java

February 23, 2022

Factorial of a number in Java :

Factorial of a number is the product of all numbers between 1 and the number itself.

  • For 0, the factorial is 1
  • For negative numbers, the factorial values are not defined
java program to find FACTORIAL OF NUMBER

Methods Discussed

  • Method 1: Iterative
  • Method 2: Recursive
  • Method 3: BigIntegers
  • Method 4: One line Ternary Operator

Method 1

  • Initialize variable fact = 1
  • Run a loop between 1 and fact with iteration in (i)
  • For each iteration in (i), multiple it with fact
  • fact = fact * i
  • Print the result
//Java program to find factorial of a number
import java.util.Scanner;
public class LearnCoding
{
    public static void main(String[] args)
    {
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter a number : ");
        int num = sc.nextInt();

        if(num >= 0)
        {
            System.out.println(num + " Factorial: " + getFact(num));
        }
        else
            System.out.println("Negative Number: No Factorial");
    }

    private static int getFact(int num) {

        if(num == 1 || num == 0)
            return 1;

        return num * getFact(num-1);
    }
}

Output

Enter a number : 5
5 factorial: 120

Method 2 (Recursive)

This method uses recursion in Java. For an input num –

  • Call a recursive function getFact(num)
  • Set base case as num == 1, return 1
  • For other cases return num * getFact(num-1);

Below is the code for the same –

//Java program to find factorial of a number
import java.util.Scanner;
public class LearnCoding
{
    public static void main(String[] args)
    {
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter a number : ");
        int num = sc.nextInt();

        if(num >= 0)
        {
            System.out.println(num + " Factorial: " + getFact(num));
        }
        else
            System.out.println("Negative Number: No Factorial");
    }

    private static int getFact(int num) {

        if(num == 1 || num == 0)
            return 1;

        return num * getFact(num-1);
    }
}

Output

Enter a number : 6
6 Factorial: 720

Method 3 (BigInteger)

Factorial of a number can be very very large. We can use long instead of int but still factorial will become big enough to not to be stored in long integers as well.

// Java program to find factorial of a number of large numbers
import java.math.BigInteger;
import java.util.Scanner;
public class LearnCoding2
{
    public static void main(String[] args)
    {
        Scanner sc = new Scanner(System.in);
        int num = 30;
        BigInteger fact = BigInteger.ONE;

        for(int i = 1; i <= num;i++)
        {
            // we are doing fact = fact * i
            // big integer multiplication happens like this
            fact = fact.multiply(BigInteger.valueOf(i));
        }

        System.out.println(num + " Factorial: \n" + fact);

    }
}

Output

30 Factorial: 
265252859812191058636308480000000

Method 4 (One line Ternary Operator)

We can use the ternary operator to find factorial in one single line.

Note this also uses recursion in Java

import java.util.Scanner;
public class LearnCoding
{
    public static void main(String[] args)
    {
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter a number : ");
        int num = sc.nextInt();

        if(num >= 0)
        {
            System.out.println(num + " Factorial: " + getFact(num));
        }
        else
            System.out.println("Negative Number: No Factorial");
    }

    private static int getFact(int num) {

    // single line to find factorial
        return (num == 1 || num == 0) ? 1 : num * getFact(num - 1);
    }
}

Output

Enter a number : 5
5 Factorial: 120

One comment on “Factorial of a number Program in Java”


  • Srikanth

    code in python
    num = int(input(“Enter a number “))
    fact=1
    if num <= 0:
    print("negative factorial")
    elif num == 1:
    print("1 is the factorial")

    else:
    for i in range(1,num+1):
    fact=fact*i
    print(fact)