JTable ClassCastException: Add rows dynamically

[Sherry Jacob]

Hi Everyone,

Heres what I wrote to implement a simple JTable.

 
   import java.io.*;
import java.util.*;
 
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.table.DefaultTableModel;
 
import java.sql.*;
 
public class TablePopulation extends JFrame
{
JTable table;
Vector cols;
Vector rows;
 
JScrollPane scrollpane;
 
DefaultTableModel model = new DefaultTableModel(new Vector(), new Vector());
 
TablePopulation()
{
Container contentpane = getContentPane();
contentpane.setLayout(new FlowLayout());
 
cols = new Vector();
cols.add("Name");
cols.add("Age");
cols.add("Qualification");
System.out.println("cols = " + cols);
 
rows = new Vector();
rows = populateVector();
System.out.println("rows = " + rows);
 
model.setDataVector(rows, cols);
table = new JTable(model);
 
scrollpane = new JScrollPane(table);
scrollpane.setPreferredSize(new Dimension(100,150));
scrollpane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED);
 
contentpane.add(scrollpane);
}
 
public static void main(String[] args) 
{
TablePopulation obj;
obj = new TablePopulation();
obj.setTitle("Table Population");
obj.setSize(350,150);
obj.setLocation(250,200);
obj.show();
obj.addWindowListener(new WindowAdapter()
{
public void windowClosing(WindowEvent we)
{
System.exit(0);
}
});
}
 
public Vector populateVector()
{
Connection con;
Statement stmt;
ResultSet rs;
 
Vector v = new Vector();

try
{
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
con = DriverManager.getConnection("jdbc :o dbc:myDSN","","");
stmt = con.createStatement();
String SQL = "SELECT * FROM table1";
rs = stmt.executeQuery(SQL);
 
while (rs.next())
{
v.add(new String(rs.getString(1)));
v.add(new String(rs.getString(2)));
v.add(new String(rs.getString(3)));
}
con.close();
System.out.println("v = " + v);
}
catch(Exception e) {System.out.println("ERROR : " + e.getMessage());}
return v;
}
}

Can anyone tell me why this code gives a the following runtime error of ClassCastException?

---------- Run Java File ----------
java.lang.ClassCastException: java.lang.String
at javax.swing.table.DefaultTableModel.justifyRows(DefaultTableModel.java:238)
at javax.swing.table.DefaultTableModel.setDataVector(DefaultTableModel.java:194)
at TablePopulation.<init>(TablePopulation.java:36)
at TablePopulation.main(TablePopulation.java:49)
Exception in thread "main"
Output completed (3 sec consumed) - Normal Termination
[ March 17, 2006: Message edited by: Sherry Jacob ]

[Ben Zung]

Sherry,
The first parameter should be a Vector of Vectors for setDataVector. Try add the "rows" returned to a new Vector and use it as the first param of setDataVector.
It makes sense coming to think that a table is a two dimension presentation of data.

The cause of your problem is that with your initializing of the table model, a String was being tried to cast into a Vector thus the error.

Good luck.
[ March 17, 2006: Message edited by: Ben Zung ]

[Ben Zung]

By the way, show() is a method inherited from Window which has been deprecated. You may want to stay away from it -- or rather all those deprecated. Use setVisible() works.
Also, you probably want to pay some attention to type safety. ie

 
cols = new Vector();
cols.add("Name");
  

I would parameterize cols like this

   
Vector<String> cols = new Vector<String>();
cols.add("Name");
 

Have fun!
[ March 17, 2006: Message edited by: Ben Zung ]