Problem with actionperformed callback

I tried to create function, what shows textdialog, when client press the buton, but the problem is that i have defined frame under public static void main and in ActionPerformed callback first parameter "frame" is undefined. How could i fix this?

import java.awt.*;

import java.awt.event.*;

import java.applet.Applet;

import javax.swing.*;

public class Vestlus extends Applet implements ActionListener {

TextField tf = new TextField("");

Button nupp = new Button(" Sisesta ");

public Vestlus()

{

add(tf);

add(nupp);

nupp.addActionListener(this);

}

public void actionPerformed(ActionEvent e)

{

if(e.getSource() == nupp)

{

JOptionPane.showMessageDialog(frame,"Hoiatus","Vää rtused ei klapi!", JOptionPane.INFORMATION_MESSAGE);

}

}

public static void main(String args[])

{

JFrame frame = new JFrame("Project LA");

frame.add(new Vestlus());

frame.setSize(300,200);

frame.setVisible(true);

frame.setDefaultCloseOperation(1);

}

}