如何在java中添加滚动条到面板,没有borderlayout？

JPanel panel = new JPanel();

// 示例：添加一个按钮到面板中
JButton button = new JButton("按钮");
panel.add(button);

JScrollPane scrollPane = new JScrollPane(panel);

scrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
scrollPane.setHorizontalScrollBarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);

frame.add(scrollPane);

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;

public class ScrollPaneExample {
    public static void main(String[] args) {
        JFrame frame = new JFrame("滚动条示例");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(300, 200);

        JPanel panel = new JPanel();
        JButton button = new JButton("按钮");
        panel.add(button);

        JScrollPane scrollPane = new JScrollPane(panel);
        scrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
        scrollPane.setHorizontalScrollBarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);

        frame.add(scrollPane);

        frame.setVisible(true);
    }
}