Question

How do you register an event listener with a JButton component?

Short answer

Answer: To register an event listener with a JButton in Java, follow these steps: 1. Import necessary packages like java.awt.event (for ActionListener) and javax.swing (for JButton). 2. Create a custom ActionListener class that implements the ActionListener interface and override the actionPerformed method to specify the action to be executed on receiving the event. 3. Create an instance of the JButton component and set its text label. 4. Register the event listener with the JButton by calling the addActionListener method and passing an instance of the custom ActionListener. 5. Add the JButton to a JPanel, set the JPanel as the main content pane of a JFrame (the window), configure the JFrame, and make it visible. When the JButton is clicked, the actionPerformed method of the custom ActionListener will be called.

Step-by-step solution

1. Import Necessary Packages

First, import the necessary packages in the Java program, mainly java.awt.event (for ActionListener) and javax.swing (for JButton): ```java import javax.swing.JButton; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import javax.swing.JFrame; import javax.swing.JPanel; ```

2. Create a Custom ActionListener

Create a custom ActionListener class that implements the ActionListener interface. In this class, override the 'actionPerformed' method to specify the action to be executed upon receiving the specified event. ```java class CustomActionListener implements ActionListener { @Override public void actionPerformed(ActionEvent e) { System.out.println("Button clicked!"); } } ```

3. Create a JButton

Create an instance of the JButton component, and set its text label: ```java JButton button = new JButton("Click me"); ```

4. Register the Event Listener with the JButton

Create a new instance of the CustomActionListener and register it to the JButton by calling the 'addActionListener' method of the JButton. ```java button.addActionListener(new CustomActionListener()); ```

5. Add JButton to Frame and Display the Frame

To display the JButton and see the event listener in action, add the JButton to a JPanel, set the JPanel as the main content pane of the JFrame (the window), configure the JFrame, and make it visible. ```java public static void main(String[] args) { // Create the JButton JButton button = new JButton("Click me"); button.addActionListener(new CustomActionListener()); // Add button to JPanel JPanel panel = new JPanel(); panel.add(button); // Configure the JFrame and display it JFrame frame = new JFrame("Button Event Listener"); frame.setContentPane(panel); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setSize(300, 150); frame.setVisible(true); } ``` Now, when the JButton is clicked, the CustomActionListener's actionPerformed method would be called, and the message "Button clicked!" will be printed in the console.