toString() representation output

I have a bug in the code and believe me I’ve run debugging many times to find what’s wrong with code but cannot understand what is wrong. I have to output the contents of 2d Arraylist. For example, if I do:

Board<String> board = new Board<String>(-4,1,-2,3,"A"); 
System.out.println(board);

it outputs me the following:

   | -2| -1|  0|  1|  2|  3|
   +---+---+---+---+---+---+
-4 |  A|  A|  A|  A|  A|  A|
   +---+---+---+---+---+---+
-3 |  A|  A|  A|  A|  A|  A|
   +---+---+---+---+---+---+
-2 |  A|  A|  A|  A|  A|  A|
   +---+---+---+---+---+---+
-1 |  A|  A|  A|  A|  A|  A|
   +---+---+---+---+---+---+
 0 |  A|  A|  A|  A|  A|  A|
   +---+---+---+---+---+---+
 1 |  A|  A|  A|  A|  A|  A|
   +---+---+---+---+---+---+

But when I change the fourth value, 3, to higher number, for example, 4 ((-4,1,-2,4,"A")), then it says:

 java.lang.IndexOutOfBoundsException: Index: 6, Size: 6

All of my constructors work well, and I assume the bug is in the toString() method. And again, I’ve tried to debug it several times but still cannot make my mind what can be wrong here. Could smb please help me? The error happens in this line inside toString() method:

Answer

You increase the row for each column:

for(int j = minCol; j <= maxCol; j++){
    secondLine1 += "|  " + myBoard.get(row++).get(col++);
    secondLine2 += "+---";
}

This is also the reason why it works for #rows >= #columns but not for #rows < #columns

Extract myBoard.get(row++) as variable before inner for loop, like

 ArrayList<T> rowCells = myBoard.get(row++);
 for(int j = minCol; j <= maxCol; j++){
       secondLine1 += "|  " + rowCells.get(col++);
       secondLine2 += "+---";
 }

and move

row = 0;

out of the outer loop.

Or, here is a suggestion with the whole class (please pay attention, I only improved the indexed access. There is enough room for further improvements, e.g string concatenations):

public class Board<T> {
private T element;
private int minCol;
private int maxCol;
private int minRow;
private int maxRow;
private int rowCount;
private int colCount;
private List<List<T>> myBoard;

public Board(int minRow, int maxRow, int minCol, int maxCol, T fillElem) {
    this.minRow = minRow;
    this.maxRow = maxRow;
    this.minCol = minCol;
    this.maxCol = maxCol;
    this.rowCount = maxRow - minRow + 1;
    this.colCount = maxCol - minCol + 1;

    if (fillElem == null) {
        throw new RuntimeException("Cannot set elements to null");
    } else {
        this.element = fillElem;
    }

    myBoard = new ArrayList<List<T>>(rowCount);
    for (int i = 0; i < rowCount; i++) {
        List<T> rowLine = new ArrayList<T>(colCount);
        myBoard.add(rowLine);
        for (int j = 0; j < colCount; j++)
            rowLine.add(element);
    }
}

private T getCellValueAt(int row, int column) {
    return myBoard.get(row - minRow).get(column - minCol);
}

@Override
public String toString() {
    StringBuilder builder = new StringBuilder();
    String result = "";
    if (this.element instanceof String) {
        String elem = (String) this.element;
        String firstLine1 = "   ";
        String firstLine2 = "   ";
        String first1 = "";
        String first2 = "";
        String secondLine1 = "";
        String secondLine2 = "   ";

        switch (elem.length()) {
        case 1:
            result = "";
            // Contructs the first two lines!
            firstLine1 = "   ";
            firstLine2 = "   ";
            first1 = "";
            first2 = "";
            for (int i = 0; i < colCount; i++) {
                if (i >= 0) {
                    first1 += "|  " + i;
                } else {
                    first1 += "| " + i;
                }
                first2 += "+---";
            }
            firstLine1 += first1 + "|n";
            firstLine2 += first2 + "+n";

            // Constrcuts the rest!
            secondLine1 = "";
            secondLine2 = "   ";

            for (int row = minRow; row <= maxRow; row++) {
                if (row >= 0) {
                    secondLine1 += " " + row + " ";
                } else {
                    secondLine1 += row + " ";
                }

                for (int column = minCol; column <= maxCol; column++) {
                    secondLine1 += "|  " + getCellValueAt(row, column);
                    secondLine2 += "+---";
                }
                secondLine1 += "|n";
                secondLine1 += secondLine2 + "+n";
                secondLine2 = "   ";

                // secondLine2 += "+n   ";
            }

            result += firstLine1 + firstLine2 + secondLine1; // + secondLine2;
            break;
        }
        return builder.append(result).toString();
    }
    return "";
}

public static void main(String[] args) {
    Board<String> board = new Board<String>(-4, 1, -2, 4, "A");
    System.out.println(board);
}

}