BtnClkDemo.java

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

public class BtnClkDemo {

  public static void main(String args[]) {
    JFrame frame = new JFrame("Button Click Demo");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    JButton button = new JButton("click Here");
    button.addActionListener(
      new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
          JOptionPane.showMessageDialog(frame, "Button Clicked!");
        }
      }
    );
    frame.getContentPane().add(button);
    frame.pack();
    frame.setVisible(true);
  }
}