How to Use Event Handlers in Java?

The following program demonstrates How to Use Event Handlers in Java.

In Java, you can use different event handlers to respond to various user interactions in a graphical user interface (GUI) application. The following code shows a Java program that demonstrates the use of different event handlers, including ActionListener, MouseListener, and KeyListener.

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

public class EventHandlersDemo {
    private JFrame frame;
    private JButton button;
    private JTextField textField;
    private JLabel label;
    private JTextArea textArea;

    public EventHandlersDemo() {
        frame = new JFrame("Event Handlers Demo");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(400, 300);

        button = new JButton("Click Me");
        textField = new JTextField(20);
        label = new JLabel("This is a label.");
        textArea = new JTextArea(5, 30);

        // ActionListener for the button
        button.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                String buttonText = button.getText();
                label.setText("Button Clicked: " + buttonText);
            }
        });

        // MouseListener for the label
        label.addMouseListener(new MouseAdapter() {
            public void mouseClicked(MouseEvent e) {
                label.setText("Label Clicked");
            }
        });

        // KeyListener for the text field
        textField.addKeyListener(new KeyAdapter() {
            public void keyTyped(KeyEvent e) {
                char keyChar = e.getKeyChar();
                textArea.append("Key Typed: " + keyChar + "\n");
            }
        });

        // Add components to the frame
        frame.setLayout(new FlowLayout());
        frame.add(button);
        frame.add(textField);
        frame.add(label);
        frame.add(textArea);

        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                new EventHandlersDemo();
            }
        });
    }
}

In this program:

We create a JFrame and set its properties, including title, close operation, and size.
Then, we create various Swing components, such as JButton, JTextField, JLabel, and JTextArea.
Next, we add event handlers to these components as follows:
- For the button, we add an ActionListener that responds when the button is clicked.
- Similarly, for the label, we add a MouseListener to detect mouse clicks.
- Likewise, for the textField, we add a KeyListener to capture key events when typing.
Inside each event handler, we perform actions such as updating labels, displaying messages in a text area, or responding to user input.
After that, we add all the components to the frame and set the frame’s layout to FlowLayout.
Finally, we make the frame visible.

When you run this program, you can interact with the GUI components and observe how different event handlers respond to button clicks, label clicks, and key typing events.

Further Reading