Lesson 1 - Java GUI

This tutorial is for anyone who wants to learn the basics of the graphical user interface in Java and thus create interesting programs. Prerequisites for this tutorial include knowledge of at least basic language constructs and basics of OOP.

What is a GUI?

The Graphical User Interface is everything the ordinary user of our program interacts with - a window containing various graphic components (buttons, icons, scrollbars ..). Using these components, the user communicates with the program. Since the 1980s, the GUI has become standard and today, we practically don't encounter a program that runs only in the command line. That's why it's a good idea to learn it

GUI and Java

In the early days of Java, designing the GUI was quite lousy, but over time it's been constantly improved. Today, Java is a fully-featured tool for creating nice window apps. Java contains two popular graphic libraries. The older AWT (Abstract Windowing Toolkit) and since JDK 1.2, there's also JFC (Java Foundation Classes) - known as Swing. In Java, all buttons, windows, text areas, etc. are called components. We place components in containers such as JFrame or JPanel.

First window

In Java, of course, there are more ways to create a basic window. In my opinion, the best one is as follows: we'll create a new project in NetBeans or Eclipse. It'll generate a class named after our project with the main() method.

We'll add a new class named Gui to our project. The Gui class will inherit from the JFrame class. Of course, we must import the library. JFrame is located in the javax.Swing.JFrame package. Just to be sure, we'll import all Swing packages using an asterisk.

In the Gui class, we'll create a parameter-less constructor. Since Java doesn't inherit constructors, we'll use the super keyword which calls the JFrame class constructor and takes the title of our window as a parameter. The Gui class looks like this:

import javax.swing.*;

public class Gui extends JFrame {

    public Gui()
    {
        super("My first window"); // the parameter is the window title
    }

}

Let's get back to the main method. We'll create a Gui class instance in it, which is our window. We'll call the following basic methods on our object:

• setVisible(true) - This method with the true parameter makes our window visible
• setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE) - Makes the program to close when the "X" window button is pressed
• window.setSize(300, 200) - A method that sets the window size (in pixels), the first parameter is the width, the second is the height.

The main class will look like this:

import javax.swing.JFrame;

public class GuiTutorial {

    public static void main(String[] args) {
        Gui window = new Gui();
        window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        window.setVisible(true);
        window.setSize(300, 200);
    }
}

If we run the program now, a window will appear in the left corner. It'd be more elegant if we centered it on the screen. To do this, we'll use the following method with a null parameter:

• setLocationRelativeTo(null)

So the main method looks like this:

public static void main(String[] args) {
    Gui window = new Gui();
    window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    window.setVisible(true);
    window.setSize(300, 200);
    window.setLocationRelativeTo(null);
}

Great, we have our first window! It should look something like this:

You can normally resize, minimize and close the window. Next time, in the lesson Java GUI - Basic Components, we'll look at adding some components.