Question

Code in Java

Create a file called Factorial.java. This file should have the following method:
public static long calculate(long n) Factorial.calculate should recursively calculate n!, where 0! = 1 and n! = n(n−1)!. The method should also print out an error and exit if n < 0 or n > 20, since factorial is not defined for negative numbers and will overflow Java’s long variable with larger numbers (if we used an int, it would overflow even sooner!). Inside Factorial.java, also include a main method which runs a couple of tests on Factorial.calculate:
java Factorial Factorial.calculate(0) returned 1. Test passed! Factorial.calculate(5) returned 120. Test passed!

Answer 1

public class Factorial {

    public static long calculate(long n) {
        if (n == 0) {
            return 1;
        } else {
            return n * calculate(n-1);
        }
    }

    public static void main(String[] args) {
        long result = Factorial.calculate(0);
        System.out.println("Factorial.calculate(0) returned " + result);
        if (result == 1) {
            System.out.println("Test passed!");
        }
        result = Factorial.calculate(5);
        System.out.println("Factorial.calculate(5) returned " + result);
        if (result == 120) {
            System.out.println("Test passed!");
        }
    }
}