Introduction to Java Swing

Introduction to Java Swing

Java Swing is a part of Java Foundation Classes (JFC) and provides a set of APIs for creating graphical user interfaces (GUIs) in Java. It is built on top of the Abstract Window Toolkit (AWT) and offers a richer set of GUI components. Swing is a platform-independent, lightweight toolkit that can be used to create window-based applications.

Key Features of Swing

1. Lightweight Components:

   • Swing components are lightweight because they are written entirely in Java and do not rely on native platform components.

2. Pluggable Look and Feel:

   • Swing supports pluggable look and feel, which means you can change the appearance of your application to match different platforms (e.g., Windows, macOS, Linux) or create a custom look and feel.

3. Component-based Architecture:

   • Swing follows a component-based architecture, allowing for reusable, modular, and easily extendable components.

4. MVC Architecture:

   • Swing components follow the Model-View-Controller (MVC) design pattern, separating the data (Model), the UI (View), and the interaction logic (Controller).

5. Event-Driven Programming:

   • Swing supports event-driven programming, where user actions (e.g., button clicks) trigger events that can be handled by event listeners.

6. Customizable Components:

   • Swing components can be customized by extending existing components or creating new ones from scratch.

Basic Components and Containers

Swing provides a rich set of components and containers that can be used to build GUIs. Here are some of the most commonly used ones:

1. JFrame:

   • The main window that contains other components.
   • Example: JFrame frame = new JFrame("My Application");

2. JPanel:

   • A generic container used to group other components.
   • Example: JPanel panel = new JPanel();

3. JButton:

   • A button that can trigger actions when clicked.
   • Example: JButton button = new JButton("Click Me");

4. JLabel:

   • A text label for displaying static text or images.
   • Example: JLabel label = new JLabel("Hello, World!");

5. JTextField:

   • A single-line text input field.
   • Example: JTextField textField = new JTextField(20);

6. JTextArea:

   • A multi-line text input area.
   • Example: JTextArea textArea = new JTextArea(5, 20);

7. JComboBox:

   • A drop-down list for selecting an item from a list of options.
   • Example: JComboBox<String> comboBox = new JComboBox<>(new String[] {"Option 1", "Option 2"});

8. JCheckBox:

   • A check box for selecting/deselecting options.
   • Example: JCheckBox checkBox = new JCheckBox("Check me");

Example: A Simple Swing Application

Here's a basic example of a Swing application that demonstrates how to create a window with a button and a label:

import javax.swing.*;

import java.awt.*;

import java.awt.event.ActionEvent;

import java.awt.event.ActionListener;

public class SimpleSwingApp {

    public static void main(String[] args) {

        // Create the main frame

        JFrame frame = new JFrame("Simple Swing Application");

        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        frame.setSize(400, 300);

        // Create a panel to hold components

        JPanel panel = new JPanel();

        frame.add(panel);

        placeComponents(panel);

        // Make the frame visible

        frame.setVisible(true);

    }

    private static void placeComponents(JPanel panel) {

        panel.setLayout(null);

        // Create a label

        JLabel label = new JLabel("Hello, Swing!");

        label.setBounds(150, 20, 100, 25);

        panel.add(label);

        // Create a button

        JButton button = new JButton("Click Me");

        button.setBounds(150, 60, 100, 25);

        panel.add(button);

        // Add action listener to the button

        button.addActionListener(new ActionListener() {

            public void actionPerformed(ActionEvent e) {

                label.setText("Button Clicked!");

            }

        });

    }

}

Explanation:

1. Creating the Frame:

   • JFrame frame = new JFrame("Simple Swing Application"); creates the main window.
   • frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); ensures the application exits when the window is closed.
   • frame.setSize(400, 300); sets the window size.

2. Creating the Panel:

   • JPanel panel = new JPanel(); creates a panel to hold other components.
   • frame.add(panel); adds the panel to the frame.
   • panel.setLayout(null); sets the layout manager to null for absolute positioning.

3. Adding Components:

   • JLabel label = new JLabel("Hello, Swing!"); creates a label.
   • JButton button = new JButton("Click Me"); creates a button.
   • Both components are added to the panel with specified bounds for positioning.

4. Handling Events:

   • button.addActionListener(new ActionListener() { ... }); adds an action listener to handle button clicks.
   • label.setText("Button Clicked!"); updates the label text when the button is clicked.

This example demonstrates the basics of creating a simple GUI application using Java Swing. Swing provides a powerful and flexible framework for building rich user interfaces in Java applications.