Grid Bag Layout

Question

Exception in thread "main" java.lang.NullPointerException
at java.awt.Container.addImpl(Compiled Code)
at java.awt.Container.add(Container.java:245)
at Login.addC(Login.java:37)
at Login.(init)(Login.java:28)
at Login.main(Login.java:44)
I get this error and it hangs all the time...what's wrong with it? I'm new to Java and this simple program is really giving me problems
import javax.swing.*;
import javax.swing.event.*;
import java.awt.*;
import java.awt.event.*;
public class Login extends JFrame
implements ActionListener{
public Login(){
setTitle("HyperSmart Login");
Container contentPane = getContentPane();
GridBagLayout gblLogin = new GridBagLayout();
GridBagConstraints gbcLogin = new GridBagConstraints();
contentPane.setLayout(gblLogin);
gbcLogin.fill = GridBagConstraints.BOTH;
gbcLogin.weightx = 0;
gbcLogin.weighty = 100;
JLabel lblUserName = new JLabel("Username");
JTextField txtUserName = new JTextField();
JLabel lblPassword = new JLabel("Password");
JPasswordField txtPassword = new JPasswordField("", 10);
addC(lblUserName, gbcLogin, 0, 0, 1, 1);
addC(txtUserName, gbcLogin, 0, 1, 3, 1);
addC(lblPassword, gbcLogin, 1, 0, 1, 1);
addC(txtPassword, gbcLogin, 1, 1, 3, 1);
addC(OKButton, gbcLogin, 2, 2, 1, 1);
public void addC(Component c, GridBagConstraints gbcLogin,
int x, int y, int w, int h){
gbcLogin.gridx = x;
gbcLogin.gridy = y;
gbcLogin.gridwidth = w;
gbcLogin.gridheight =h;
getContentPane().add(c, gbcLogin);
public void actionPerformed(ActionEvent e){
public static void main(String[] args){
Login frmLogin = new Login();
frmLogin.show();
JButton OKButton;

Answer 1

you get nullPointer because OKButton is null.
after
JPasswordField txtPassword = new JPasswordField("", 10);
just write OKButton = new JButton("OK");