# Calculate factorial of a number in Java using recursion

Carvia Tech | December 25, 2019 | 2 min read | 76 views |

Factorial of a number is calculated using below formula:

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

the factorial of a number is calculated by formula `number * (number -1)` till zero and since the value of factorial zero is 1, it acts as a base case in the recursive version of the factorial method.

## Recursive approach

Recursive function to calculate factorial
``````public class Factorial {
public long factorial(long n) {
if (n == 1)
return 1;
else {
return n * factorial(n - 1);
}
}
}``````

## Iterative approach

Iterative approach for factorial
``````class Scratch {
public long fact(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.

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:

###### Java Coding Challenges:
See all articles in Java Coding Challenges

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