 # Java Program to Find Factorial of a Number

To understand this example, you should have the knowledge of the following Java programming topics:

The factorial of a positive number n is given by:

```factorial of n (n!) = 1 * 2 * 3 * 4 * ... * n
```

## Example 1: Find Factorial of a number using for loop

``````public class Factorial {

public static void main(String[] args) {

int num = 10;
long factorial = 1;
for(int i = 1; i <= num; ++i)
{
// factorial = factorial * i;
factorial *= i;
}
System.out.printf("Factorial of %d = %d", num, factorial);
}
}``````

Output

`Factorial of 10 = 3628800`

In this program, we've used for loop to loop through all numbers between 1 and the given number num (10), and the product of each number till num is stored in a variable factorial.

We've used long instead of int to store large results of factorial. However, it's still not big enough to store the value of bigger numbers (say 100).

For results that cannot be stored in a long variable, we use `BigInteger` variable declared in `java.math` library.

## Example 2: Find Factorial of a number using BigInteger

``````import java.math.BigInteger;

public class Factorial {

public static void main(String[] args) {

int num = 30;
BigInteger factorial = BigInteger.ONE;
for(int i = 1; i <= num; ++i)
{
// factorial = factorial * i;
factorial = factorial.multiply(BigInteger.valueOf(i));
}
System.out.printf("Factorial of %d = %d", num, factorial);
}
}``````

Output

`Factorial of 30 = 265252859812191058636308480000000`

Here, instead of `long`, we use `BigInteger` variable factorial.

Since, `*` cannot be used with `BigInteger`, we instead use `multiply()` for the product. Also, num should be casted to `BigInteger` for multiplication.

Likewise, we can also use a while loop to solve this problem.

## Example 3: Find Factorial of a number using while loop

``````public class Factorial {

public static void main(String[] args) {

int num = 5, i = 1;
long factorial = 1;
while(i <= num)
{
factorial *= i;
i++;
}
System.out.printf("Factorial of %d = %d", num, factorial);
}
}``````

Output

`Factorial of 5 = 120`

In the above program, unlike a for loop, we have to increment the value of i inside the body of the loop.

Though both programs are technically correct, it is better to use for loop in this case. It's because the number of iteration (upto num) is known.

Visit this page to learn to find factorial of a number using recursion.