Simple AWT Java Application

//MyFirstUI.java
package ui;

import java.awt.*;
import java.awt.event.*;

import javax.swing.*;


public class MyFirstUI extends JFrame implements ActionListener{

    /**
     *
     */
    private static final long serialVersionUID = 1L;
    private JCheckBox checkbox;
    private JTextField firstName;
    private JTextField lastName;

    public MyFirstUI() {

        // Lets make it look nice
        // This you can ignore / delete if you don't like it
        // try {
        // for (LookAndFeelInfo info : UIManager.getInstalledLookAndFeels()) {
        // if ("Nimbus".equals(info.getName())) {
        // UIManager.setLookAndFeel(info.getClassName());
        // break;
        // }
        // }
        // } catch (Exception e) {
        // e.printStackTrace();
        // }

        setTitle("My First UI");

        // We create a panel which will hold the UI components
        JPanel pane = new JPanel(new BorderLayout());
        // We always have two UI elements (columns) and we have three rows
        int numberOfRows = 3;
        int numberOfColumns = 2;
        pane.setLayout(new GridLayout(numberOfRows, numberOfColumns));

        // create and attach buttons
        // create a label and add it to the main window
        JLabel firstNamelabel = new JLabel(" Firstname: ");
        pane.add(firstNamelabel);
        firstName = new JTextField();
        pane.add(firstName);

        JLabel lastNamelabel = new JLabel(" Lastname: ");
        pane.add(lastNamelabel);
        lastName = new JTextField();
        pane.add(lastName);

        JButton sayHello = new JButton("Say something");
        pane.add(sayHello);

        checkbox = new JCheckBox("Nice");
        pane.add(checkbox);

        // Add the pane to the main window
        getContentPane().add(pane);

        // Pack will make the size of window fitting to the compoents
        // You could also use for example setSize(300, 400);
        pack();

        // Set a tooltip for the button
        sayHello.setToolTipText("This button will say something really nice of something bad");
        // sayHello need to do something
        sayHello.addActionListener(this);
    }
    public void actionPerformed(ActionEvent e) {
        if (!checkbox.isSelected()) {
            JOptionPane.showMessageDialog(null, "I don't like you, "
                    + firstName.getText() + " " + lastName.getText() + "!");
        } else {
            JOptionPane.showMessageDialog(null, "How are you, "
                    + firstName.getText() + " " + lastName.getText() + "?");
        }
    }


}

//MainTester.java
package test;

import ui.MyFirstUI;

public class MainTester {
    public static void main(String[] args) {
        MyFirstUI view = new MyFirstUI();
        view.setVisible(true);
    }
}