JavaAlgorithms/Maths/Factorial.java

package Maths;

public class Factorial {

  /* Driver Code */
  public static void main(String[] args) {
    assert factorial(0) == 1;
    assert factorial(1) == 1;
    assert factorial(5) == 120;
    assert factorial(10) == 3628800;
  }

  /**
   * Calculate factorial N using iteration
   *
   * @param n the number
   * @return the factorial of {@code n}
   */
  public static long factorial(int n) {
    if (n < 0) {
      throw new IllegalArgumentException("number is negative");
    }
    long factorial = 1;
    for (int i = 1; i <= n; factorial *= i, ++i)
      ;
    return factorial;
  }
}