JTable columns do not resize when setPreferredWidth is called

Question

EDIT: As suggested by camickr, I added the JTable to a scrollpane. It seems that he/she was correct that the layout manager was altering the size of the columns.

I have a JTable with 50 rows and 40 columns. Each cell displays either nothing, or a single character.

I am trying to make each cell square by setting the row height and column width to the same value.

public IFace() {
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setBounds(100, 100, 966, 740);

    JMenuBar menuBar = new JMenuBar();
    setJMenuBar(menuBar);

    mntmFile = new JMenuItem("File");
    menuBar.add(mntmFile);
    contentPane = new JPanel();
    contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
    setContentPane(contentPane);
    contentPane.setLayout(new MigLayout("", "[457.00,grow][grow]", "[][grow][center][][grow]"));

    JToolBar toolBar = new JToolBar();
    contentPane.add(toolBar, "cell 0 0");

    lblPalette = new JLabel("Palette");
    contentPane.add(lblPalette, "cell 1 0");

    AsciiTableModel myTableModel = new AsciiTableModel();
    tableASCII = new JTable(myTableModel);
    tableASCII.getSelectionModel();
    tableASCII.getSelectionModel().setSelectionMode(ListSelectionModel.MULTIPLE_INTERVAL_SELECTION);
    tableASCII.setCellSelectionEnabled(true);

    tableASCII.setAutoResizeMode(JTable.AUTO_RESIZE_OFF);
    System.out.println(tableASCII.getColumnModel().getColumn(0).getMaxWidth());
    final int cellSize = 20;

    for(int i = 0; i < tableASCII.getColumnCount(); i++){
        tableASCII.getColumnModel().getColumn(i).setPreferredWidth(cellSize);
        System.out.println(tableASCII.getColumnModel().getColumn(i).getWidth());
    }

    for(int i = 0; i < tableASCII.getRowCount(); i++){
        tableASCII.setRowHeight(i, cellSize );
    }


    contentPane.add(tableASCII, "cell 0 1,span 0 5");

    btnFill = new JButton("Fill");
    contentPane.add(btnFill, "flowx,cell 1 2");

    textFill = new JTextField();
    textFill.setHorizontalAlignment(SwingConstants.CENTER);
    contentPane.add(textFill, "cell 1 2");
    textFill.setColumns(10);
}

After calling setPreferredWidth(cellSize), the output of System.out.println(tableASCII.getColumnModel().getColumn(i).getWidth()); is 75. It should be 20.

This is the code for the tablemodel that tableASCII uses.

public class AsciiTableModel extends AbstractTableModel {

public final int NUM_CHARACTERS_PER_CELL = 1;
private int numColumns = 50;
private int numRows = 40;
private List<ArrayList<Character>> asciiChars = new ArrayList<ArrayList<Character>>();

public AsciiTableModel() {
    createListElements();
    System.out.println(asciiChars.get(0).size());
    asciiChars.get(2).set(0, 'C');
    asciiChars.get(1).set(0, 'a');
    asciiChars.get(1).set(1, 't');


}

public AsciiTableModel(int rows, int columns) {
    numColumns = columns;
    numRows = rows;
}

@Override
public int getColumnCount() {
    // TODO Auto-generated method stub
    return numColumns;
}

@Override
public int getRowCount() {
    // TODO Auto-generated method stub
    return numRows;
}

@Override
public Object getValueAt(int rowIndex, int columnIndex) {
    // TODO Auto-generated method stub
    return asciiChars.get(rowIndex).get(columnIndex);
}
public boolean isCellEditable(int rowIndex, int columnIndex) {
    return true;
}

@Override
public void setValueAt(Object aValue, int rowIndex, int columnIndex) {
    if(aValue != null) {
        //System.out.println(aValue.toString());
        asciiChars.get(rowIndex).set(columnIndex, aValue.toString().charAt(1));
        //System.out.println(asciiChars.get(rowIndex).get(columnIndex));
    }
}


void createListElements() {
    for(int i = 0; i < numRows; i++) {
        asciiChars.add(new ArrayList<Character>());
        for(int j = 0; j < numColumns; j++) {
            asciiChars.get(i).add(' ');
        }
    }
}

Answer 1

The width does not get determined until the doLayout() method is invoked on the table. This is done when you pack() the frame and all components get layed out at their preferred sizes.

Once the frame is made visible the columns will display at its preferred width. If you are still having problems, then post a SSCCE that uses the DefaultTableModel and a standard layout manager.

contentPane.add(tableASCII, "cell 0 1,span 0 5");

If the columns are not displayed as you like it is probably because you are not adding the table to a scrollpane and MigLayout is affecting the table columns sizes.