Java でのボタンクリックイベント

package delftstack;

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

class ActionEventDemo implements ActionListener {
  JFrame Demo_Frame = new JFrame();
  JButton Demo_Button = new JButton("Click Here");

  ActionEventDemo() {
    Prepare_GUI();
    Button_Properties();
  }

  public void Prepare_GUI() {
    Demo_Frame.setTitle("Demo Window");
    Demo_Frame.getContentPane().setLayout(null);
    Demo_Frame.setVisible(true);
    Demo_Frame.setBounds(400, 100, 400, 400);
    Demo_Frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  }
  public void Button_Properties() {
    Demo_Button.setBounds(150, 200, 150, 80);
    Demo_Frame.add(Demo_Button);
    Demo_Button.addActionListener(this);
  }

  @Override
  public void actionPerformed(ActionEvent e) {
    // Changing Background Color
    Demo_Frame.getContentPane().setBackground(Color.red);
  }
}

public class On_Click {
  public static void main(String[] args) {
    new ActionEventDemo();
  }
}