Question

I have accepted various types of data inputs (integer, double, string and date) to my embedded JDBC database via (JTextLabels EDIT: JTextFields) using ResultSet and i am displaying results in a swing JTable using my custom AbstractTableModel. The following are snippets from my codes where am thinking the problem might lie, but i’m not sure;

public void connectToDB()
    {
        try
        {
            connection = DriverManager.getConnection(DBURL, DBUSERNAME, DBPASSWORD);
            statement = connection.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE, ResultSet.CONCUR_UPDATABLE);
            connectedToDB = true;
        }
        catch (SQLException sqlEx)
        {
            sqlEx.printStackTrace();
        }
    }

//Overrides AbstractTableModel's getValueAt() method
    public Object getValueAt(int row, int column) throws IllegalStateException
    {
        connectToDB();
        if (connectedToDB == false)
            throw new IllegalStateException ("Not Connected To database");
        else
        {
            try
            {
                if ( resultSet.next() == true )
                {
                    resultSet.absolute( row + 1 );
                    return resultSet.getObject( column + 1 );
                }
            }
            catch (SQLException sqlEx)
            {
                sqlEx.printStackTrace();
            }
        }
        return "";// returns an empty string Object in case an error occurs above
    }

It looks as if somwhere around the getValueAt() method, it generates the following exception, but even the stacktrace doesnt point me to any part of my code;

Exception in thread "AWT-EventQueue-0" java.lang.IllegalArgumentException: Cannot format given Object as a Number
    at java.text.DecimalFormat.format(DecimalFormat.java:487)
    at java.text.Format.format(Format.java:140)
    at javax.swing.JTable$DoubleRenderer.setValue(JTable.java:5315)
    at javax.swing.table.DefaultTableCellRenderer.getTableCellRendererComponent(DefaultTableCellRenderer.java:223)
    at javax.swing.JTable.prepareRenderer(JTable.java:5683)
    at javax.swing.JTable.getToolTipText(JTable.java:3328)
............ 
*Others ommitted 4 brevity*
............

I dont know why.

Answer 1

The stacktrace indicates the problem is situated in the renderer of the table. The JTable has decided it will use the DoubleRenderer for that particular value, and that value can not be parsed to a Double. I would suggest to check your TableModel#getColumnClass implementation and see whether it returns Double.class for a column which actually does not contain Doubles since that is the method which is used to determine which renderer to use.

This can be seen in the source code for JTable, more specifically in the source of the getRenderer method. See below for the relevant part (line 3454 in the source code I linked to)

 TableCellRenderer renderer = null;
 if (columnModel.getColumnCount() > 0)
   renderer = columnModel.getColumn(column).getCellRenderer();
 if (renderer == null)
   {
     int mcolumn = convertColumnIndexToModel(column);
     renderer = getDefaultRenderer(dataModel.getColumnClass(mcolumn));
   }
 return renderer;