DefaultTableModel Problem

Question

Dear all,
I am trying to build a JTable with the below class. If I extend AbstractTableModel my code is working fine but with DefaultTableModel I get the exception: "Exception caught in ...: null".
Why do I get null exception in this code? I can't create an instance of the below class with DefaultTableModel.
!!!Please notice that the code is working fine with AbstractTableModel but not with DefaultTableModel!!!
//CLASS_1
MyTableModel myModel = new MyTableModel();
JTable costTable = new JTable(myModel);
//CLASS_2
import javax.swing.JTable;
import javax.swing.table.AbstractTableModel;
import javax.swing.table.DefaultTableModel;
import javax.swing.JScrollPane;
import javax.swing.JFrame;
import javax.swing.SwingUtilities;
import javax.swing.JOptionPane;
import java.awt.*;
import java.awt.event.*;
import java.lang.*;
import javax.swing.DefaultCellEditor;
import java.util.Vector;
//public class MyTableModel extends AbstractTableModel
public class MyTableModel extends DefaultTableModel
private boolean DEBUG = true;
final String[] columnNames = {"IFCOBJECTS OR PROCESSES", "QUANTITY", "UNITS", "UNIT COST (?)", "TOTAL COST (?)"};
static Object[][] data = new Object[IFC_Tree.totalVector.size()][5];
static double totalCost = 0.0;
public MyTableModel()
for(int m=0; m < IFC_Tree.totalVector.size(); m++)
Vector tmp = (Vector)(IFC_Tree.totalVector.elementAt(m));
for(int n=0; n < tmp.size(); n++)
Object value = tmp.get(n);
data[m][n] = value;
public int getColumnCount()
return columnNames.length;
public int getRowCount()
return data.length;
public String getColumnName(int col)
return columnNames[col];
public Object getValueAt(int row, int col)
return data[row][col];
public boolean isCellEditable(int row, int col)
if (col < 3)
return false;
else if (col == 3)
return true;
else
return false;
public void setValueAt(Object value, int row, int col)
data[row][col] = value;
fireTableCellUpdated(row, col);
if(col == 3)
try
String str = (String)data[row][col];
data[row][col+1] = new Double( ((Float)data[row][col-2]).doubleValue() * Double.valueOf(str).doubleValue() );
fireTableCellUpdated(row, col+1);
totalCost = 0.0;
for (int k=0; k<TableDemo.costTable.getRowCount(); k++)
totalCost = totalCost + ((Double)data[k][4]).doubleValue();
data[TableDemo.costTable.getRowCount() - 1][4] = new Double (totalCost);
fireTableCellUpdated(TableDemo.costTable.getRowCount() - 1, 4);
catch(Exception ex)
System.out.println("Exception caught in MyTableModel class: INVALID INPUT " + ex.getMessage());
System.out.println(":-(");
}

Answer 1

could it possibly be that:
DefaultTableModel has a vector for the data. You're trying to implement some methods that use your Object[][] but the DefaultTableModel methods want to use the vector that it supplies.