Java adds code instances of four methods for event listening

Several ways to add events in Java (reprinted from codebrother's article with minor changes) :

class EventListener1 extends JFrame implements ActionListener {
  private JButton btBlue, btDialog;

  public EventListener1() {
    setTitle("Java GUI  Event monitoring processing ");
    setBounds(100, 100, 500, 350);
    setLayout(new FlowLayout());
    btBlue = new JButton(" blue ");   
    btDialog = new JButton(" Popup window ");
    
    //Adds an event listener to the button
    btBlue.addActionListener(this);
    btDialog.addActionListener(this);

    add(btBlue);
    add(btDialog);

    setVisible(true);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  }
  //* * * * * * * * * * * * * * * * * * * * * * * * * * * event handling * * * * * * * * * * * * * * * * * * * * * * * * * * *
  @Override
  public void actionPerformed(ActionEvent e) {
    if (e.getSource() == btBlue) {
      Container c = getContentPane();
      c.setBackground(Color.BLUE);
    }
    else if (e.getSource() == btDialog) {
      JDialog dialog = new JDialog();
      dialog.setBounds(300, 200, 400, 300);
      dialog.setVisible(true);
    }
  }

}



class EventListener3 extends JFrame {
  private JButton btBlue, btDialog;

  //A constructor
  public EventListener3() {
    setTitle("Java GUI  Event monitoring processing ");
    setBounds(100, 100, 500, 350);
    setLayout(new FlowLayout());
    btBlue = new JButton(" blue ");
    btDialog = new JButton(" Popup window ");
    //Adding an event listener object (object-oriented idea)
    btBlue.addActionListener(new ColorEventListener());
    btDialog.addActionListener(new DialogEventListener());

    add(btBlue);
    add(btDialog);
    setVisible(true);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  }
  //The inner class ColorEventListener implements the ActionListener interface
  class ColorEventListener implements ActionListener {
    @Override
    public void actionPerformed(ActionEvent e) {
      Container c = getContentPane();
      c.setBackground(Color.BLUE);
    }
  }
  //The inner class DialogEventListener implements the ActionListener interface
  class DialogEventListener implements ActionListener {
    @Override
    public void actionPerformed(ActionEvent e) {
      JDialog dialog = new JDialog();
      dialog.setBounds(300, 200, 400, 300);
      dialog.setVisible(true);
    }
  }

}


class EventListener2 extends JFrame {
  private JButton btBlue, btDialog;

  public EventListener2() {
    setTitle("Java GUI  Event monitoring processing ");
    setBounds(100, 100, 500, 350);
    setLayout(new FlowLayout());

    btBlue = new JButton(" blue ");
    btDialog = new JButton(" Popup window ");
    
    //Add an event listener (anonymous class here)
    btBlue.addActionListener(new ActionListener() {
      //The event processing
      @Override
      public void actionPerformed(ActionEvent e) {
        Container c = getContentPane();
        c.setBackground(Color.BLUE);
      }
    });
    
    //And add an event listener
    btDialog.addActionListener(new ActionListener() {
      @Override
      public void actionPerformed(ActionEvent e) {
        JDialog dialog = new JDialog();
        dialog.setBounds(300, 200, 400, 300);
        dialog.setVisible(true);
      }
    });

    add(btBlue);
    add(btDialog);
    setVisible(true);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  }

}


class EventListener4 extends JFrame {
  private JButton btBlue, btDialog;

  public EventListener4() {
    setTitle("Java GUI  Event monitoring processing ");
    setBounds(100, 100, 500, 350);
    setLayout(new FlowLayout());
    btBlue = new JButton(" blue ");
    btDialog = new JButton(" Popup window ");
    //Adds an event listener to the button
    btBlue.addActionListener(new ColorEventListener(this));
    btDialog.addActionListener(new DialogEventListener());

    add(btBlue);
    add(btDialog);
    setVisible(true);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  }

}
//The external class ColorEventListener implements the ActionListener interface
class ColorEventListener implements ActionListener {
  private EventListener4 el;
  ColorEventListener(EventListener4 el) {
    this.el = el;
  }
  @Override
  public void actionPerformed(ActionEvent e) {
    Container c = el.getContentPane();
    c.setBackground(Color.BLUE);
  }
}
//The external DialogEventListener class implements the ActionListener interface
class DialogEventListener implements ActionListener {
  @Override
  public void actionPerformed(ActionEvent e) {
    JDialog dialog = new JDialog();
    dialog.setBounds(300, 200, 400, 300);
    dialog.setVisible(true);
  }
}

public class ActionListenerTest
{
  public static void main(String args[])
  {
    new EventListener2();
  }
}