Que aviso é este? "The serializable class Form10 does not declare a static final"

import java.awt.BorderLayout;
import java.awt.Color;
import javax.swing.*;
import java.awt.event.*;

public class Form extends JFrame{
	
    double v1, v2, v3;

    private JLabel lbl_v1;
    private JTextField jtf_v1;

    private JButton btn_b1;

    private JPanel pnl_p1;

private void initComponents(){

    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setTitle("exemplo");

    lbl_v1 = new JLabel();
    lbl_v1.setText("label 1");
    lbl_v1.setVisible(true);

    jtf_v1 = new JTextField();
    jtf_v1.requestFocus();
    jtf_v1.setVisible(true);
    jtf_v1.setSize(20,40);

    btn_b1 = new JButton();
    btn_b1.setText("Sair");
    btn_b1.setMnemonic('r');
    btn_b1.setVisible(true);
    btn_b1.addActionListener(new btn_b1Listener());

    pnl_p1 = new JPanel();
    pnl_p1.setVisible(true);
    pnl_p1.setBackground(Color.GRAY);

    pnl_p1.add(lbl_v1);
    pnl_p1.add(jtf_v1);
    pnl_p1.add(btn_b1);

    getContentPane().add(BorderLayout.NORTH, pnl_p1);

}
public static void main(String[] args) {
	Form janela = new Form();
	janela.initComponents();
	janela.setVisible(true);
	janela.pack();
}

class btn_b1Listener implements ActionListener {
    public void actionPerformed(ActionEvent e) {
        dispose();
      }
    }