test PROG 21.3.

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

public class Test extends JFrame{
    private JPanel mainPanel;
    private JTextField nameField;
    private JTextField surnameField;
    private JCheckBox checkBox;
    private JButton button1;
    private JMenu menuFile;
    private JMenuItem chooseFile;
    private JMenuItem reset;

    public Test(){
        initComponents();
        button1.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
            nameField.setText("Karel");
            surnameField.setText("Dvořák");
            }
        });
    }
    public void initComponents(){
        setContentPane(mainPanel);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JMenuBar menuBar = new JMenuBar();
        setJMenuBar(menuBar);
        menuFile = new JMenu("Operace");
        menuBar.add(menuFile);
        chooseFile = new JMenuItem("Ulož do souboru...");
        menuFile.add(chooseFile);
        reset = new JMenuItem("Resetuj formulář");
        menuFile.add(reset);
        chooseFile.addActionListener(e -> openFile());
        reset.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                nameField.setText(null);
                surnameField.setText(null);
                checkBox.setSelected(false);
            }
        });
    }
    public void openFile() {
        JFileChooser fc = new JFileChooser();
        fc.showOpenDialog(this);
        File vysledek = fc.getSelectedFile();
        try {
            Writer writer = new FileWriter(vysledek);
            writer.append(nameField+"\n");
            writer.append(surnameField+"\n");
            if(checkBox.isSelected()){
                writer.append("umí\n");
            }
            else {
                writer.append("neumí\n");
            }

        } catch (IOException e) {
            throw new RuntimeException();
        }
    }


    public static void main(String[] args) {
        Test t = new Test();
        t.setTitle("Operace");
        t.pack();
        t.setVisible(true);
    }
}