Java by API/java.awt.event/ActionListener

implements ActionListener

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class MainClass extends JPanel {
  public MainClass() {
    JButton btn1 = new JButton("Button1");
    btn1.addActionListener(new ButtonListener());
    add(btn1);
  }
  public static void main(String[] args) {
    JFrame frame = new JFrame();
    frame.getContentPane().add(new MainClass());
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(200, 200);
    frame.setVisible(true);
  }
}
class ButtonListener implements ActionListener {
  ButtonListener() {
  }
  public void actionPerformed(ActionEvent e) {
    if (e.getActionCommand().equals("Button1")) {
      System.out.println("Button1 has been clicked");
    }
  }
}