Java错误：javax.swing.JTable $ 1无法强制转换为javax.swing.table.DefaultTableModel

Question

What I'm trying to do is I am creating a JTable inside a new instance of JPanel and JFrame and I am getting the error upon adding the rows in the table:

Object[] column = {"id", "title"};
Object[][] data = {};
JTable toDoTable = new JTable(data, column) {
  public Component prepareRenderer(TableCellRenderer renderer, int rowIndex,
      int columnIndex) {
       if(columnIndex == 1) {
          setFont(new Font("Arial", Font.BOLD, 12));
       } else {
           setFont(new Font("Arial", Font.ITALIC, 12));
       }

         return super.prepareRenderer(renderer, rowIndex, columnIndex);
  }
};


JScrollPane jpane = new JScrollPane(toDoTable);
JPanel panel = new JPanel();
JFrame frame = new JFrame();
frame.setSize(new Dimension(1100, 408));
frame.setTitle("JTable Font Setting Example");
panel.add(jpane);
frame.add(new JScrollPane(panel));
frame.setVisible(true);

// Add rows in the Table
DefaultTableModel model = (DefaultTableModel)toDoTable.getModel();
ConnectMSSQLServer connServer = new ConnectMSSQLServer();
ResultSet rs = connServer.dbConnect();
  try
   {
      while (rs.next()) {
          String id = rs.getString("id");
          String title = rs.getString("title");
          model.addRow(new Object[]{id, title});
      }
    }
    catch(Exception e)
    {

    }

The error occurs in the add rows in table

Answer 1

Your problem here is that you are invoking the JTable(Object[][], Object[]) constructor. If you check out the source code in that link, you can see that it is invoking the JTable(TableModel) constructor internally, having constructed an anonymous instance of AbstractTableModel , which is what is returned by the getModel() method - this can't be cast to a DefaultTableModel .

However: what you are trying to do here won't work anyway. You are saying that the rows of the data are represented by a zero-element array:

Object[][] data = {};

You will not be able to add rows to this, because you can't resize an array once constructed.

Instead of this, you should construct an explicit DefaultTableModel :

TableModel tableModel = new DefaultTableModel(column, rowCount);

and then use this to construct the JTable :

JTable toDoTable = new JTable(tableModel) { ... }

I am not familiar with swing at all, but it looks like DefaultTableModel is backed by a Vector for the row data, so you don't need to know the exact value of rowCount up front.

Answer 2

Consider this slightly changed code:

    //Create the new model for the table
    DefaultTableModel model = new DefaultTableModel();

    ConnectMSSQLServer connServer = new ConnectMSSQLServer();
    //Try with catch for auto-closing result set
    try(ResultSet rs = connServer.dbConnect()) {
        while (rs.next()) {
            String id = rs.getString("id");
            String title = rs.getString("title");
            model.addRow(new Object[] { id, title });
        }
    } catch (Exception e) {
        //HANDLE THIS!
    }
    //Now populate the table with the new model
    toDoTable.setModel(model);