public static int numFives (double[] a) {
    return numFives (0, 0);
  }
  private static int numFives (int i, int result) {
    if (i>=a.length) 
      return result;
    if (a[i] == 5.0) 
      return numFives (i+1, result+1);
    else
      return numFives (i+1, result);
  }