# Java Program to find Factorial of a number

Upasana | October 17, 2020 | 2 min read | 382 views |

Factorial of a number is calculated using below mathematical formula:

`factorial (n) = n x (n-1) x (n-2) ... 1`

In Java, we can either use iterative approach or recursive approach to calculate the factorial. We will discuss both of them in this article.

## Recursive approach

The factorial of a number can be expressed by this recursive function:

`factorial (n) = n x factorial (n-1)`

till n becomes 1 i.e. till factorial of 0 (which is one).

Recursive function to calculate factorial
``````public class Factorial {
public long factorial(long n) {
if (n == 1)     (1)
return 1;
else {
return n * factorial(n - 1);    (2)
}
}
}``````
 1 Base condition for recursive method. Factorial of Zero is One. 2 We multiply number with factorial of `(number - 1)` to get factorial of a number

## Iterative approach

Iterative approach is bit simple, where we multiply all numbers from 1 to n and return the result.

Iterative approach for factorial
``````class Scratch {
public long factorial(long number) {
long result = 1L;
while (number != 0) {
result = result * number;
number--;
}
return result;
}
}``````

## Factorial using Java 8 Streams

Java 8 streams with reduction method can be used to calculate factorial of a number. This is a iterative approach, but instead of loops we are using streams.

java 8 Streams for factorial calculation
``````import java.util.stream.LongStream;

class Scratch {
public static long factorialStreams(long n) {
return LongStream.rangeClosed(2, n)
.reduce(1, (long a, long b) -> a * b);
}
}``````
• LongStream.rangeClosed(2, n) method creates a Stream of longs from [2 to n].

• Lambda function supplied for reduce `(a,b) → a * b` will multiply each pair of `a` and `b` and return the result. The result then carries over to `a` for the next round. The value of `1` is used in the reduction method as the starting value for variable `a` for the first iteration.

## Handling very large numbers

Here we are using `long` to hold the result of multiplication, which can quickly overflow due to maximum limit an long can hold. We can improve the above two programs to use BigInteger as discussed in the below article:

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