Java GUI Programming

In addition to command-line and web applications, Java can also create feature-rich desktop Graphical User Interface (GUI) applications. Java provides two main GUI toolkits: Swing and JavaFX.

• AWT (Abstract Window Toolkit): Java's earliest GUI toolkit, heavily dependent on the native operating system's GUI components. It is rarely used directly now.
• Swing: Built on top of AWT, providing richer, more flexible "lightweight" components (completely drawn by Java), achieving a cross-platform consistent look and feel.
• JavaFX: As Swing's modern successor, it provides a more modern API, CSS support, 3D graphics, and richer media capabilities. Starting from JDK 11, JavaFX has been separated from the standard library and needs to be added as a separate module.

This chapter will mainly introduce the classic Swing.

Swing Basics

A Swing application typically consists of the following core parts:

1. Top-Level Containers: The starting point of a GUI, serving as the carrier for all other components.

   • JFrame: Represents a standard window with a title bar, border, and control buttons (minimize, maximize, close).
   • JDialog: Represents a dialog box.
   • JApplet: Used for Java applets running in browsers (now obsolete).

2. Intermediate Containers: Used to organize and layout other components.

   • JPanel: The most commonly used general-purpose container, which can be thought of as a canvas for grouping components.

3. Atomic Components: Basic controls that users interact with directly.

   • JButton: Button.
   • JLabel: Text label.
   • JTextField: Single-line text input field.
   • JTextArea: Multi-line text area.
   • JCheckBox: Checkbox.
   • JRadioButton: Radio button.

Creating Your First Swing Window

import javax.swing.JFrame;

public class FirstWindow {
    public static void main(String[] args) {
        // 1. Create a JFrame object
        JFrame frame = new JFrame("My First GUI Window");

        // 2. Set the default operation when the window is closed
        // EXIT_ON_CLOSE means exit the application when the window is closed
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        // 3. Set the window size (unit: pixels)
        frame.setSize(400, 300);

        // 4. Make the window visible
        frame.setVisible(true);
    }
}

Layout Managers

Layout managers are responsible for determining the size and position of components in a container. Directly setting the absolute coordinates of components (null layout) is not recommended because it cannot adapt to different screen sizes and resolutions.

• FlowLayout: The default layout for JPanel. Components are arranged from left to right like flowing water, and automatically wrap when one line cannot fit.
• BorderLayout: The default layout for JFrame. Divides the container into five regions: NORTH, SOUTH, EAST, WEST, CENTER.
• GridLayout: Divides the container into a grid of equal-sized cells, with each component occupying one cell.

Event Handling

GUI applications are event-driven. When users interact with components (such as clicking a button), an event is generated. We need to write Event Listeners to respond to these events.

Example: A Simple Counter

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

public class CounterApp {
    private static int count = 0;

    public static void main(String[] args) {
        JFrame frame = new JFrame("Simple Counter");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(300, 200);

        // Create a panel
        JPanel panel = new JPanel();
        frame.add(panel);

        // Create components
        JLabel label = new JLabel("Click count: 0");
        JButton button = new JButton("Click me!");

        // Add components to the panel
        panel.add(label);
        panel.add(button);

        // Add event listener to the button
        button.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                // Code to execute when the event occurs
                count++;
                label.setText("Click count: " + count);
            }
        });

        frame.setVisible(true);
    }
}

About JavaFX

While Swing is still available and powerful, for new desktop application projects, JavaFX is Oracle's officially recommended modern alternative. It provides a richer API, supports FXML (an XML-based markup language for defining interfaces), can use CSS for styling, and better integrates modern hardware acceleration features. If you plan to dive deeper into Java GUI development, JavaFX is a direction worth investing time in.