The Slice.match method contains a loop, which checks if matching hit the end of the input on each iteration:

            for (int j=0; j<len; j++) {
                if ((i+j) >= matcher.to) {
                    matcher.hitEnd = true;
                    return false;
                }
                if (buf[j] != seq.charAt(i+j))
                    return false;
            }

It would be more efficient to move this check out of the loop and do it only once.