Even though the isWin method is not the scope of the last test, it can still be refactored even more. For once, we don't need to check all the combinations, but only those related to the position of the last piece played. The final version could look like the following:
private boolean isWin(int x, int y) { int playerTotal = lastPlayer * 3; char horizontal, vertical, diagonal1, diagonal2; horizontal = vertical = diagonal1 = diagonal2 = '\0'; for (int i = 0; i < SIZE; i++) { horizontal += board[i][y - 1]; vertical += board[x - 1][i]; diagonal1 += board[i][i]; diagonal2 += board[i][SIZE - i - 1]; } if (horizontal == playerTotal || vertical == playerTotal || diagonal1 == playerTotal || diagonal2 == playerTotal) { return true; } return ...
