Okieninio

package com.company;

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

public class Okno extends JFrame {

    static JPanel karty;

    public Okno(int w_okno, int h_okno) {
        super("Witaj w grze!");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(w_okno, h_okno);
        setResizable(false);
        setLocationRelativeTo(null);

        Menu menu = new Menu();
        Poziomy lvl = new Poziomy();
        Etap_1 e_1 = new Etap_1();

        karty = new JPanel(new CardLayout());
        karty.add(menu, "menu");
        karty.add(lvl, "poziomy");
        karty.add(e_1, "etap_1");
        add(karty, BorderLayout.CENTER);
        setVisible(true);
    }
}