Factorial

Sum of Two Numbers Sum Multiples of Three and Five Factorial Linear Search Reverse String Find Maximum Average Value (Java 8 Lambdas and Streams) Convert to Upper Case (Java 8 Lambdas and Streams) Nth Odd Element Number Of Tree Nodes Count Nodes in List Count Number of Leaf Nodes Binary Tree Depth Find Second Largest Number in Array

Write a method that calculates the factorial of a given number.
Factorial is the product of all positive integers less than or equal to n. For example, factorial(4) = 4x3x2x1 = 24.
TIP: To make it more interesting, try to do it recursively.

public Integer factorial(Integer n) {

}