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