Thread: exception in "main" java.lang.NullPointerException

Error:

Exception in thread "main" java.lang.NullPointerException
at adminlogin.launchframe(adminlogin.java:30)
at adminlogin.main(adminlogin.java:68)

my code is:


import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.io.*;

public class adminlogin implements ActionListener//,FocusListener
{

private JFrame f;
private JLabel l1,l2,l3;
private JTextField tf1;
private JPasswordField pf1;
private JButton b1;

public adminlogin()
{

l1=new JLabel("Admin Login");
l2=new JLabel("Enter Username");
l3=new JLabel("Enter Password");
tf1=new JTextField();
pf1=new JPasswordField();
b1=new JButton("Login");

}

public void launchframe()
{

f.setLayout(null);
f.add(l1);
f.add(l2);
//f.add(l3);
f.add(tf1);
//f.add(pf1);
//f.add(b1);

l1.setBounds(600,200,100,25);
l2.setBounds(500,250,150,25);
tf1.setBounds(600,250,150,25);


f.setSize(2000,2000);
f.setVisible(true);

}

public void actionPerformed(ActionEvent e)
{
/*
if(e.getSource()==b1)
{
staffdata sd=new staffdata();
sd.launchframe();
f.setVisible(false);
}*/

}

/*public void focusLost(FocusEvent fe)
{}
public void focusGained(FocusEvent fe1)
{}*/

public static void main(String args[])
{
adminlogin ac =new adminlogin();
ac.launchframe();
}

}


pls help me to solve this problem!!!!
urgent!!!
thanks in advance

You never initialized the variable f. That's why it's throwing that exception.

Also, when comparing objects like JButtons or Strings, use .equals(Object obj) method instead of ==.