🔘 JButton & ActionListener

1️⃣ Introduction to JButton

A JButton is a clickable button in Java Swing. It allows users to trigger actions when clicked.

Why Use JButton?

✔️ Provides a simple interactive component
✔️ Supports event handling with ActionListener
✔️ Can be customized (size, icon, text, color, etc.)

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2️⃣ Creating a Simple JButton

Example: Adding a Button to JFrame

import javax.swing.*;

public class JButtonExample {
    public static void main(String[] args) {
        // Create frame
        JFrame frame = new JFrame("JButton Example");
        frame.setSize(300, 200);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

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

        // Add button to frame
        frame.add(button);

        // Make frame visible
        frame.setVisible(true);
    }
}

Explanation

• JButton button = new JButton("Click Me"); → Creates a button with text.
• frame.add(button); → Adds the button to the frame.
• Clicking the button does nothing yet (we need an event listener).

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3️⃣ Handling Button Clicks with ActionListener

Example: Adding ActionListener to JButton

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

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

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

        // Add ActionListener to the button
        button.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                JOptionPane.showMessageDialog(null, "Button Clicked!");
            }
        });

        frame.add(button);
        frame.setVisible(true);
    }
}

Explanation

✔️ button.addActionListener(...) → Registers a click event.
✔️ JOptionPane.showMessageDialog(...) → Shows a popup message.

📌 Now, when you click the button, a message appears!

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4️⃣ Using Lambda Expression (Simpler Syntax)

Java 8+ allows lambda expressions, making event handling cleaner.

Example: Using a Lambda for ActionListener

button.addActionListener(e -> JOptionPane.showMessageDialog(null, "Button Clicked!"));

✔️ Less code
✔️ Easier to read
✔️ Works only in Java 8+

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5️⃣ Handling Multiple Buttons

Example: Multiple Buttons with Different Actions

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

public class MultipleButtonsExample {
    public static void main(String[] args) {
        JFrame frame = new JFrame("Multiple Buttons");
        frame.setSize(400, 200);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JPanel panel = new JPanel();

        JButton btn1 = new JButton("Say Hello");
        JButton btn2 = new JButton("Say Goodbye");

        // Add event handlers
        btn1.addActionListener(e -> JOptionPane.showMessageDialog(null, "Hello!"));
        btn2.addActionListener(e -> JOptionPane.showMessageDialog(null, "Goodbye!"));

        // Add buttons to panel
        panel.add(btn1);
        panel.add(btn2);

        frame.add(panel);
        frame.setVisible(true);
    }
}

Explanation

✔️ btn1 → Shows "Hello!" when clicked.
✔️ btn2 → Shows "Goodbye!" when clicked.
✔️ Multiple buttons can have different actions.

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6️⃣ Changing Button Text, Icon, and Style

Example: Customizing a JButton

import javax.swing.*;
import java.awt.*;

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

        JButton button = new JButton("Click Me");
        button.setFont(new Font("Arial", Font.BOLD, 16));
        button.setBackground(Color.BLUE);
        button.setForeground(Color.WHITE);

        frame.add(button);
        frame.setVisible(true);
    }
}

Explanation

✔️ setFont(new Font("Arial", Font.BOLD, 16)); → Sets font style & size.
✔️ setBackground(Color.BLUE); → Sets background color.
✔️ setForeground(Color.WHITE); → Sets text color.

📌 You can fully customize buttons in Swing!

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7️⃣ Disabling & Enabling Buttons

Example: Disable Button After Click

import javax.swing.*;

public class DisableButtonExample {
    public static void main(String[] args) {
        JFrame frame = new JFrame("Disable Button Example");
        frame.setSize(300, 200);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

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

        button.addActionListener(e -> {
            button.setEnabled(false); // Disable the button
            JOptionPane.showMessageDialog(null, "Button Disabled!");
        });

        frame.add(button);
        frame.setVisible(true);
    }
}

Explanation

✔️ button.setEnabled(false); → Disables the button after clicking.
✔️ setEnabled(true); → Re-enables the button (if needed).

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8️⃣ Closing the Application with a Button

Example: Exit Button (System.exit(0))

JButton exitButton = new JButton("Exit");
exitButton.addActionListener(e -> System.exit(0));

✔️ Closes the app when clicked.
✔️ System.exit(0); → Terminates the program.

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🔥 Summary

✅ JButton creates interactive buttons.
✅ ActionListener handles button clicks.
✅ Use lambda expressions for simpler event handling.
✅ Customize buttons with text, color, and font.
✅ Disable/Enable buttons as needed.