GCD: admissible values for the arguments

What happens in the previous algorithm in the following cases:

• If x = y = 0?
  The result is 0.
• If x = 0 and y > 0 (or vice-versa)?
  The result should be y, but the algorithm enters an infinite loop.
• If x < 0 and y is arbitrary (or vice-versa)?
  The algorithm enters an infinite loop.

Hence, if we want to take into account that the method could be called with arbitrary integer values for the parameters, it is necessary to insert a suitable test.

public static int greatestCommonDivisor(int x, int y) {
  if ((x > 0) && (y > 0)) {
    while (x != y)
      if (x > y)
        x = x - y;
      else              // this means that y > x
        y = y - x;
    return x;
  } else
    System.out.println("wrong parameters");
}