MyAnonymousInner.java

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

public class MyAnonymousInner {

  public static void main(String args[]) {
    SwingUtilities.invokeLater(() -> {
      JFrame frame = new JFrame("Anonymous Inner Class");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      JPanel panel = new JPanel();
      panel.setPreferredSize(new Dimension(300, 200));
      JButton button = new JButton("Click Here");
      button.addActionListener(
        new ActionListener() {
          @Override
          public void actionPerformed(ActionEvent e) {
            JOptionPane.showMessageDialog(frame, "Button Clicked!");
          }
        }
      );
      panel.add(button);
      frame.add(panel);
      frame.pack();
      frame.setVisible(true);
    });
  }
}