Java GUI cant find a mistake

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Java

GUI

package kalkulacka;

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


public class Lalala extends JFrame {
	
	
	
	private JTextField vloz1;
	private JButton stlac; 
	private JTextField vloz2; 
	private JLabel label_vysledok; 
	private JPanel lajna1; 
	private JPanel lajna2; 
	
	public Lalala(){
		super ("Kalkulacka");
		FlowLayout layout = new FlowLayout();
		setLayout(layout);
		
		lajna1 = new JPanel();
		lajna1.setBackground(Color.blue);
		add(lajna1);
		
		lajna2 = new JPanel();
		lajna2.setBackground(Color.LIGHT_GRAY);
		add(lajna2);
		
		vloz1 = new JTextField(); 
		lajna1.add(vloz1);
		vloz2 = new JTextField(); 
		lajna1.add(vloz2);
		stlac = new JButton();
		lajna1.add(stlac);
		
		label_vysledok = new JLabel();
		lajna2.add(label_vysledok);
	}
}

package kalkulacka;

import javax.swing.JFrame;

public class Kalkulacka {

	public static void main(String[] args) {
		Lalala okno = new Lalala(); 
		okno.setVisible(true);
		okno.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		okno.setLocationRelativeTo(null);
		
		

	}

}

What I have tried:

One code is a GUI (Lalala) of kalkulacka. I tried add a parameters to class Lala methods. Then I tried change position of setBackground and other methods. Nothing worked. Eclipse saying me this problem:

The serializable class Lalala does not declare a static final serialVersionUID field of type long

but I dont know what Eclipse mean..

I am solving this problem for two hour without a result.