Problem in populating jtable data from database

Question

hi,
i am using JTable to retrieve data from database and show it in table. JTable
is working fine with static data. but while retrieving from databse its giving a NullPointerException at getColumnClass() method. Below is complete source code. plzz help.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
import java.sql.*;
import javax.swing.table.*;
/*jdbc connection class*/
class connect
Connection con;
Statement stat;
public connect()throws Exception
Class.forName("org.postgresql.Driver");
con=DriverManager.getConnection("jdbc:postgresql://localhost/dl","dl","dl");
stat=con.createStatement();
public ResultSet rsf(String rsstr)throws Exception
ResultSet rs=stat.executeQuery(rsstr);
return rs;
public void upf(String upstr)throws Exception
stat.executeUpdate(upstr);
class MyTableModel extends AbstractTableModel
private String[] columnNames = {"name","id","dep","cat","rem","chkout"};
Object[][] data;
public MyTableModel()
try{
connect conn=new connect();
ResultSet rs3=conn.rsf("select * from usertab");
ResultSetMetaData rsmd=rs3.getMetaData();
int col=rsmd.getColumnCount();
int cou=0;while(rs3.next()){cou++;}
data=new Object[cou][col];
System.out.println(cou+" "+col);
ResultSet rs2=conn.rsf("select * from usertab");
int i=0;int j=0;
for(i=0;i<cou;i++)
rs2.next();
for(j=0;j<col;j++)
data[i][j]=rs2.getString(getColumnName(j));
System.out.println(data[0][2]);
}catch(Exception e){System.out.println("DFD "+e);}
        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 Class getColumnClass(int c) {
          return getValueAt(0, c).getClass();
        public boolean isCellEditable(int row, int col) {
            if (col < 2) {
                return false;
            } else {
                return true;
        public void setValueAt(Object value, int row, int col) {
            data[row][col] = value;
            fireTableCellUpdated(row, col);
class MyFrame extends JFrame
public MyFrame()
     setSize(600,500);
     JPanel p1=new JPanel();
     p1.setBackground(new Color(198,232,189));
     JTable table = new JTable(new MyTableModel());
     table.setPreferredScrollableViewportSize(new Dimension(500,200));
     table.setBackground(new Color(198,232,189));
     JScrollPane scrollPane = new JScrollPane(table);
     scrollPane.setBackground(new Color(198,232,189));
     p1.add(scrollPane);
     getContentPane().add(p1);
/*Main Class*/
class test2
     public static void main(String args[])
     MyFrame fr =new MyFrame();
     fr.setVisible(true);
}thanx

Answer 1

hi nickelb,
i had returned Object.class in the getColumnClass() method. But then i
got NullPointerException at getRowCount() method. i could understand that the
main problem is in data[][] object. In all the methods its returning null values as it is so declared outside the construtor. But if i declare the object inside the constructor, then the methods could not recognize the object. it seems i cant do the either ways. hope u understood the problem.
thanx