A programming puzzle

Here's an interesting programming puzzle. Who can spot the bug in the following simple code, which implements a binary search? The array is sorted.

01 public static int binarySearch(int[] a, int key) {

02 int low = 0;

03 int high = a.length - 1;

04 

05 while (low <= high) {

06 int mid = (low + high) / 2;

07 int midVal = a[mid];

08 

09 if (midVal < key)

10 low = mid + 1;

11 else if (midVal > key)

12 high = mid - 1;

13 else

14 return mid; // key found

15 }

16 return -(low + 1); // key not found.

17 }
 
 

Java2html

I freely admit I couldn't figure it out. It isn't that simple. Whoever gets it has my full admiration! I'll just add that this code was part of the Java API for years…