如何使用Java在Swing GUI中通过单击按钮打开新窗口

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

JFrame mainFrame = new JFrame("主窗口");
mainFrame.setSize(400, 300);
mainFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

JButton openButton = new JButton("打开新窗口");
openButton.addActionListener(new ActionListener() {
    @Override
    public void actionPerformed(ActionEvent e) {
        // 在此处编写打开新窗口的代码
    }
});

class NewWindow extends JFrame {
    public NewWindow() {
        setTitle("新窗口");
        setSize(300, 200);
        setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
    }
}

openButton.addActionListener(new ActionListener() {
    @Override
    public void actionPerformed(ActionEvent e) {
        NewWindow newWindow = new NewWindow();
        newWindow.setVisible(true);
    }
});

mainFrame.getContentPane().setLayout(new FlowLayout());
mainFrame.getContentPane().add(openButton);

mainFrame.setVisible(true);