what does ">>>" mean in java?

Question

I found this code to find duplicates in SO post here. but I dont understand what this line means int mid = (low + high) >>> 1;

private static int findDuplicate(int[] array) {
        int low = 0;
        int high = array.length - 1;

        while (low <= high) {
            int mid = (low + high) >>> 1;
            System.out.println(mid);
            int midVal = array[mid];

            if (midVal == mid)
                low = mid + 1;
            else
                high = mid - 1;
        }
        return high;
    }

Answer 1

The >>> operator is the unsigned right bit-shift operator in Java. It effectively divides the operand by 2 to the power of the right operand, or just 2 here.

The difference between >> and >>> would only show up when shifting negative numbers. The >> operator shifts a 1 bit into the most significant bit if it was a 1, and the >>> shifts in a 0 regardless.

UPDATE:

Let's average 1 and 2147483647 (Integer.MAX_VALUE). We can do the math easily:

(1 + 2147483647) / 2 = 2147483648 / 2 = 1073741824

Now, with the code (low + high) / 2, these are the bits involved:

          1: 00000000 00000000 00000000 00000001
+2147483647: 01111111 11111111 11111111 11111111
================================================
-2147483648: 10000000 00000000 00000000 00000000  // Overflow
/2
================================================
-1073741824: 11000000 00000000 00000000 00000000  // Signed divide, same as >> 1.

Let's make the "shift" to >>>:

          1: 00000000 00000000 00000000 00000001
+2147483647: 01111111 11111111 11111111 11111111
================================================
-2147483648: 10000000 00000000 00000000 00000000  // Overflow
>>> 1
================================================
+1073741824: 01000000 00000000 00000000 00000000  // Unsigned shift right.