Demo 01 : Event Handling

import javax.swing.*;
import java.awt.*; // Layout
// Step 1
import java.awt.event.*; // Event

public class Demo01 extends JFrame
  /*Step 2*/     implements ActionListener{
  
  private JButton btn1;
  private JPanel northPanel;
  
  public Demo01(){
    btn1 = new JButton("Button 1");
    northPanel = new JPanel();
    northPanel.add(btn1);
    getContentPane().add(northPanel, 
                         BorderLayout.NORTH);
    // Step 4: 
    btn1.addActionListener(this);
  }//end constructor
  
  
  // Step 3: add this method
  public void actionPerformed(ActionEvent ev){
    JOptionPane.showMessageDialog(null,
             "Hi,you clicked button 1");
  }//end actionPerformed

  
}//end class