TextField and Button Example in Java

import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JTextField;

public class TextFieldAndButtonTutorial extends JFrame implements
        ActionListener {

    /*
     * Creating instances of text fields, buttons and a panel that we will use
     * in this tutorial
     */
    JTextField txtField;
    JButton btn1, btn2, btn3;
    JPanel pnl;

    /*
     * In this constructor we will initialize all the UI components and them to
     * the Panel. One new thing that we will be doing is the Event Handling in
     * this tutorial. Events are basically actions that we want the program to
     * perform when we click on a button. For this tutorial we will cover just
     * one type of event listener which is used for clicking events. Its is
     * called "ActionListener".
     */
    public TextFieldAndButtonTutorial() {
        /*
         * This super calls the constructor of JFrame class that we extended and
         * arguments passed in it set that as the title of the window.
         */
        super("A simple TextField and Button tutorial");
        /*
         * Setting the Layout as simple FlowLayout
         */
        setLayout(new FlowLayout());

        /*
         * Initializing all the components
         */
        pnl = new JPanel();
        /*
         * We are initializing the TextField and passing an argument of 15 in
         * the JTextField constructor to set the length of the TextField.
         */
        txtField = new JTextField(15);
        /*
         * Here JButtons are being initialized. The text passed as the argument
         * in the constructor will be the title that we will be see on buttons.
         */
        btn1 = new JButton("Enable Text Field");
        btn2 = new JButton("Disable Text Field");
        btn3 = new JButton("Submit");

        /*
         * adding all the components in the JPanel object and adding the JPanel
         * object in the Frame
         */
        pnl.add(txtField);
        pnl.add(btn1);
        pnl.add(btn2);
        pnl.add(btn3);
        add(pnl);

        /*
         * Now this one is new. What this code do is it registers the button
         * components to the click events. But what we want to perform on these
         * events will be done in a seperate method of ActionListener interface
         * that we implemented in this class.
         */
        btn1.addActionListener(this);
        btn2.addActionListener(this);
        btn3.addActionListener(this);
        /*
         * In the above methods "this" is passed as an argument because the
         * method of the ActionListener interface is in the same class. There
         * are several methods to perform this functionality using multiple
         * classes. Those will be discussed in the next 2-3 tutorials before
         * discussing other event listeners.
         */
    }

    /*
     * This is the method of the ActionListener interface. It will be called
     * when we click on a button that is registered to the ActionListener
     * events. i.e. btn1.addActionListener(this);
     */
    @Override
    public void actionPerformed(ActionEvent e) {
        /*
         * What we are doing here is we are recogonizing the button clicked by
         * the ActionEvent class's method getSource(). What this getSource()
         * method do is recogonize which button was clicked and then we can
         * perform the desired operation by recogonizing the compoment object
         */
        if (e.getSource() == btn1) {
            txtField.setEnabled(true);
        } else if (e.getSource() == btn2) {
            txtField.setEnabled(false);
        } else if (e.getSource() == btn3) {
            String message = txtField.getText();

            if (message.equals("")) {
                JOptionPane.showMessageDialog(null, "Please enter something. You have left the field empty");
            } else {
                /*
                 * This is a way to show a message dialog box.
                 * More of it will be discussed in a later tutorial
                 */
                JOptionPane.showMessageDialog(null, "You entered: " + message);
            }
        }
    }

    public static void main(String[] args) {
        TextFieldAndButtonTutorial obj = new TextFieldAndButtonTutorial();
        obj.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        obj.setSize(700, 200);
        obj.setResizable(false);
        obj.setVisible(true);

    }
}