Generování a vypsání čísla v okně

import javax.swing.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class GUI extends JFrame {
    private JTextField textField1;
    private JButton generujButton;
    private JButton kopírujButton;
    private JTextArea textArea1;
    private JPanel panelMain;


    public GUI() {
        generujButton.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
            double randomDouble = Math.random()*100;
            int random = (int) Math.round(randomDouble);

            textField1.setText(String.valueOf(random));
            }
        });
        kopírujButton.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
            textArea1.append(textField1.getText()+"\n");
            }
        });

    }

    public static void main(String[] args) {
        GUI gui = new GUI();
        gui.setVisible(true);
        gui.setTitle("náhodné číslo");
        gui.setContentPane(gui.panelMain);
        gui.setSize(300, 200);
        gui.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
}