Bit twiddling eight-direction loop.

Foo.java

// Get dr, dc values to move in all eight directions in a 2d array
// with a loop that only iterates exactly eight times.
for (int i = 0; i < 8; i++) {
  int dr = (i & 3) == 0 ? 0 : (1 - ((i & 4) >> 1));
  int dc = (i - 2 & 3) == 0 ? 0 : (1 - ((i - 2 & 4) >> 1));
  IO.println("%2d, %2d".formatted(dr, dc));
}