Post_90.3.java

public abstract class GameWinnerDetector {

    protected String findBoardWinner(int boardLength) {

        for (int index = 0; index < boardLength; index++) {
            addGamePiecesToList(index);
        }
        return checkIfWinnerExists();
    }

    protected abstract void addGamePiecesToList(int index);
    protected abstract String checkIfWinnerExists();
}

public class LeftDiagonalWinnerDetector extends GameWinnerDetector {
    private Board board;
    private WinnerValidator winnerValidator;
    private String[] lineValues;

    public LeftDiagonalWinnerDetector(Board board, WinnerValidator winnerValidator) {
        this.board = board;
        this.winnerValidator = winnerValidator;
        this.lineValues = new String[board.getMatrix().length];
    }

    @Override
    protected void addGamePiecesToList(int index) {
        lineValues[index] = winnerValidator.getValueAtIndex(board, index, index);
    }

    @Override
    protected String checkIfWinnerExists() {
        return winnerValidator.checkDiagonalsForWin(board, lineValues);
    }
}

public class WinnerValidator {

    public String checkDiagonalsForWin(Board board, String[] lineValues) {
      if (isWinningCombo(board, lineValues)) {
         return lineValues[0];
      }
      return "";
    }

    public String checkRowsAndColumnsForWin(Board board, String[][] lineValues) {
        for (int i = 0; i < board.getMatrix().length; i++) {
            if (isWinningCombo(board, lineValues[i])) {
                return lineValues[i][0];
            }
        } return "";
    }

    public String getValueAtIndex(Board board, int startingIndex, int endingIndex) {
        return board.getMatrix()[startingIndex][endingIndex];
    }

    public boolean isWinningCombo(Board board, String[] lineValues) {
        String first = lineValues[0];
        for (String value : lineValues) {
            if (value != first || value == board.getBoardEmptySpace()) {
                return false;
            }
        }
        return true;
    }
}