Post_90.2.java

    private String checkColumns() {
        int boardLength = board.getMatrix().length;
        int maxIndexValue = boardLength - 1;
        String[][] lineValues = new String[boardLength][boardLength];

        for (int columnIndex = 0; columnIndex < boardLength; columnIndex++) {
            for (int index = 0; index < boardLength; index++) {
                lineValues[columnIndex][index] = getValueAtIndex(columnIndex, maxIndexValue - index);
            }
        }

        for (int i = 0; i < boardLength; i++) {
            if (isWinningCombo(lineValues[i])) {
                return lineValues[i][0];
            }
        }

        return "";
    }

    private String checkRows() {
        int boardLength = board.getMatrix().length;
        int maxIndexValue = boardLength - 1;
        String[][] lineValues = new String[boardLength][boardLength];

        for (int rowIndex = 0; rowIndex < boardLength; rowIndex++) {
            for (int index = 0; index < boardLength; index++) {
                lineValues[rowIndex][index] = getValueAtIndex(maxIndexValue - index, rowIndex);
            }
        }

        for (int i = 0; i < boardLength; i++) {
            if (isWinningCombo(lineValues[i])) {
                return lineValues[i][0];
            }
        }
        return "";
    }

    private String checkRightDiagonal() {
        int boardLength = board.getMatrix().length;
        int maxIndexValue = boardLength - 1;
        String[] lineValues = new String[boardLength];

        for (int index = 0; index < boardLength; index++) {
            lineValues[index] = getValueAtIndex(index, maxIndexValue - index);
        }

        if (isWinningCombo(lineValues)) {
            return lineValues[0];
        }
        return "";
    }

    private String checkLeftDiagonal() {
        int boardLength = board.getMatrix().length;
        String[] lineValues = new String[boardLength];

        for (int index = 0; index < boardLength; index++) {
            lineValues[index] = getValueAtIndex(index, index);
        }

        if (isWinningCombo(lineValues)) {
            return lineValues[0];
        }
        return "";
    }

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

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