projt

[smjsarsji]

Please help me soon!

I am getting the following error in the program I have provided below. "Exception in thread "main" java.lang.NullPointerException." Can anyone help me?

Exception in thread "main" java.lang.NullPointerException
at ProductInfo.<init>(ProductInfo.java:37)
at ProductInfo.main(ProductInfo.java:172)


import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.sql.*;
public class ProductInfo extends JFrame implements ActionListener{
JLabel heading,id,desc,rate,quantity,unit_of_msr,empty_la bel,error;
JTextField idField,descField,rateField,quantityField,unit_of_ msrField;
JButton insert,update,delete,clear,exit;
GridBagLayout gbl;
GridBagConstraints gbc;
JComboBox idCombo;
Connection con;
PreparedStatement stat;
Statement stmt;
ResultSet rs;
Font f;
JPanel jpl;
public ProductInfo()
{
try
{
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
con=DriverManager.getConnection("jdbc:odbc:MyDataS ource","scott"," ");
stmt=con.createStatement();
rs=stmt.executeQuery("SELECT p_id FROM product");
while(rs.next())
{
idCombo.addItem(Integer.toString(rs.getInt(1)));
}
con.close();
}
catch(Exception e)
{
System.out.println("error: "+e);
}
idCombo.addActionListener(this);
}
public void actionPerformed(ActionEvent ae)
{
if(ae.getActionCommand()=="Exit")
System.exit(0);
if(ae.getActionCommand()=="Delete")
{
try
{
con=DriverManager.getConnection("jdbc:odbc:MyDataS ource","scott"," ");
stat=con.prepareStatement("DELETE from product WHERE p_id=?");
String selected_id=idCombo.getSelectedItem().toString();
int id=Integer.parseInt(selected_id);
stat.setInt(1,id);
stat.executeUpdate();
con.close();
idCombo.removeActionListener(this);
con=DriverManager.getConnection("jdbc:odbc:MyDataS ource","scott"," ");
stmt=con.createStatement();
rs=stmt.executeQuery("SELECT p_id FROM product");
idCombo.removeAllItems();
while(rs.next())
idCombo.addItem(Integer.toString(rs.getInt(1)));
con.close();
idCombo.addActionListener(this);
idField.setText("");
descField.setText("");
rateField.setText("");
quantityField.setText("");
unit_of_msrField.setText("");
error.setText("row deleted");
}
catch(Exception e)
{
System.out.println("error" +e);
error.setText("row cannot be deleted");
}
}
if(ae.getActionCommand()=="Insert")
{
try
{
con=DriverManager.getConnection("jdbc:odbc:MyDataS ource","scott"," ");
stat=con.prepareStatement("INSERT INTO product VALUES(?,?,?,?,?)");
String id=idField.getText();
String description=descField.getText();
String rate=rateField.getText();
String quantity=quantityField.getText();
String unit_of_msr=unit_of_msrField.getText();
stat.setInt(1,Integer.parseInt(id));
stat.setString(2,description);
stat.setDouble(3,Double.parseDouble(rate));
stat.setInt(4,Integer.parseInt(quantity));
stat.setString(5,unit_of_msr);
stat.executeUpdate();
con.close();
idCombo.removeActionListener(this);
con=DriverManager.getConnection("jdbc:odbc:MyDataS ource","scott"," ");
stmt=con.createStatement();
rs=stmt.executeQuery("SELECT p_id FROM product");
idCombo.removeAllItems();
while(rs.next())
idCombo.addItem(Integer.toString(rs.getInt(1)));
con.close();
idCombo.addActionListener(this);
error.setText("row inserted");
}
catch(Exception e)
{
System.out.println("error" +e);
error.setText("row cannot be inserted");
}
}
if(ae.getSource() == idCombo)
{
try
{
con=DriverManager.getConnection("jdbc:odbc:MyDataS ource","scott"," ");
String selected_id=idCombo.getSelectedItem().toString();
int id=Integer.parseInt(selected_id);
stmt=con.createStatement();
rs=stmt.executeQuery("SELECT p_desc,p_rate,p_qty,unit_of_msr FROM product WHERE p_id=" + id);
rs.next();
idField.setText(selected_id);
descField.setText(rs.getString(1));
rateField.setText(Double.toString(rs.getDouble(2)) );
quantityField.setText(Integer.toString(rs.getInt(3 )));
unit_of_msrField.setText(rs.getString(4));
con.close();
}
catch(Exception e)
{
System.out.println("error" +e);
}
}
if(ae.getActionCommand()=="Update")
{
try
{
con=DriverManager.getConnection("jdbc:odbc:MyDataS ource","scott"," ");
stat=con.prepareStatement("UPDATE product SET p_desc=?,p_rate=?,p_qty=?,unit_of_msr=? where p_id=?" );
String description=descField.getText();
String rate=rateField.getText();
String quantity=quantityField.getText();
String unit_of_msr=unit_of_msrField.getText();
String id_selected=idField.getText();
int id=Integer.parseInt(id_selected);

stat.setString(1,description);
stat.setDouble(2,Double.parseDouble(rate));
stat.setInt(3,Integer.parseInt(quantity));
stat.setString(4,unit_of_msr);
stat.setInt(5,id);
stat.executeUpdate();
con.close();
error.setText("row updated");
}
catch(Exception e)
{
System.out.println("error" +e);
error.setText("row cannot be updated");
}
}
if(ae.getActionCommand()=="Clear")
{
idField.setText("");
descField.setText("");
rateField.setText("");
quantityField.setText("");
unit_of_msrField.setText("");
}
}
public static void main(String args[])
{
ProductInfo p=new ProductInfo();
p.show();
}
}

[Norm]

java.lang.NullPointerException
at ProductInfo.<init>(ProductInfo.java:37)

What code is at line 37? What variable on that line is null?

[eRaaaa]

idCombo.addItem
idCombo.addActionListener(this); --> idCombo is null! create an instance first!

btw:
strings are objects, use equals instead of == ! (even if it works here because of the pool...)
show() is deprecated, use setVisible(true) !

[smjsarsji]

sorry 4 forgetting the line number

i provide the code along with line number which was shown as error


import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.sql.*;
public class ProductInfo extends JFrame implements ActionListener{
JLabel heading,id,desc,rate,quantity,unit_of_msr,empty_la bel,error;
JTextField idField,descField,rateField,quantityField,unit_of_ msrField;
JButton insert,update,delete,clear,exit;
GridBagLayout gbl;
GridBagConstraints gbc;
JComboBox idCombo;
Connection con;
PreparedStatement stat;
Statement stmt;
ResultSet rs;
Font f;
JPanel jpl;
public ProductInfo()
{
try
{
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
con=DriverManager.getConnection("jdbc:odbc:MyDataS ource","scott"," ");
stmt=con.createStatement();
rs=stmt.executeQuery("SELECT p_id FROM product");
while(rs.next())
{
idCombo.addItem(Integer.toString(rs.getInt(1)));
}
con.close();
}
catch(Exception e)
{
System.out.println("error: "+e);
}
line 37 idCombo.addActionListener(this);
}
public void actionPerformed(ActionEvent ae)
{
if(ae.getActionCommand()=="Exit")
System.exit(0);
if(ae.getActionCommand()=="Delete")
{
try
{
con=DriverManager.getConnection("jdbc:odbc:MyDataS ource","scott"," ");
stat=con.prepareStatement("DELETE from product WHERE p_id=?");
String selected_id=idCombo.getSelectedItem().toString();
int id=Integer.parseInt(selected_id);
stat.setInt(1,id);
stat.executeUpdate();
con.close();
idCombo.removeActionListener(this);
con=DriverManager.getConnection("jdbc:odbc:MyDataS ource","scott"," ");
stmt=con.createStatement();
rs=stmt.executeQuery("SELECT p_id FROM product");
idCombo.removeAllItems();
while(rs.next())
idCombo.addItem(Integer.toString(rs.getInt(1)));
con.close();
idCombo.addActionListener(this);
idField.setText("");
descField.setText("");
rateField.setText("");
quantityField.setText("");
unit_of_msrField.setText("");
error.setText("row deleted");
}
catch(Exception e)
{
System.out.println("error" +e);
error.setText("row cannot be deleted");
}
}
if(ae.getActionCommand()=="Insert")
{
try
{
con=DriverManager.getConnection("jdbc:odbc:MyDataS ource","scott"," ");
stat=con.prepareStatement("INSERT INTO product VALUES(?,?,?,?,?)");
String id=idField.getText();
String description=descField.getText();
String rate=rateField.getText();
String quantity=quantityField.getText();
String unit_of_msr=unit_of_msrField.getText();
stat.setInt(1,Integer.parseInt(id));
stat.setString(2,description);
stat.setDouble(3,Double.parseDouble(rate));
stat.setInt(4,Integer.parseInt(quantity));
stat.setString(5,unit_of_msr);
stat.executeUpdate();
con.close();
idCombo.removeActionListener(this);
con=DriverManager.getConnection("jdbc:odbc:MyDataS ource","scott"," ");
stmt=con.createStatement();
rs=stmt.executeQuery("SELECT p_id FROM product");
idCombo.removeAllItems();
while(rs.next())
idCombo.addItem(Integer.toString(rs.getInt(1)));
con.close();
idCombo.addActionListener(this);
error.setText("row inserted");
}
catch(Exception e)
{
System.out.println("error" +e);
error.setText("row cannot be inserted");
}
}
if(ae.getSource() == idCombo)
{
try
{
con=DriverManager.getConnection("jdbc:odbc:MyDataS ource","scott"," ");
String selected_id=idCombo.getSelectedItem().toString();
int id=Integer.parseInt(selected_id);
stmt=con.createStatement();
rs=stmt.executeQuery("SELECT p_desc,p_rate,p_qty,unit_of_msr FROM product WHERE p_id=" + id);
rs.next();
idField.setText(selected_id);
descField.setText(rs.getString(1));
rateField.setText(Double.toString(rs.getDouble(2)) );
quantityField.setText(Integer.toString(rs.getInt(3 )));
unit_of_msrField.setText(rs.getString(4));
con.close();
}
catch(Exception e)
{
System.out.println("error" +e);
}
}
if(ae.getActionCommand()=="Update")
{
try
{
con=DriverManager.getConnection("jdbc:odbc:MyDataS ource","scott"," ");
stat=con.prepareStatement("UPDATE product SET p_desc=?,p_rate=?,p_qty=?,unit_of_msr=? where p_id=?" );
String description=descField.getText();
String rate=rateField.getText();
String quantity=quantityField.getText();
String unit_of_msr=unit_of_msrField.getText();
String id_selected=idField.getText();
int id=Integer.parseInt(id_selected);

stat.setString(1,description);
stat.setDouble(2,Double.parseDouble(rate));
stat.setInt(3,Integer.parseInt(quantity));
stat.setString(4,unit_of_msr);
stat.setInt(5,id);
stat.executeUpdate();
con.close();
error.setText("row updated");
}
catch(Exception e)
{
System.out.println("error" +e);
error.setText("row cannot be updated");
}
}
if(ae.getActionCommand()=="Clear")
{
idField.setText("");
descField.setText("");
rateField.setText("");
quantityField.setText("");
unit_of_msrField.setText("");
}
}
public static void main(String args[])
{
line 171 ProductInfo p=new ProductInfo();
p.show();
}
}