JButton上的setVisible()在构造函数外部不起作用

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.SwingUtilities;

public class ButtonExample extends JFrame {
    private JButton button;

    public ButtonExample() {
        initialize();
        setupUI();
        setVisible(true);
    }

    private void initialize() {
        // 初始化窗口设置
        setTitle("Button Example");
        setSize(300, 200);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

    private void setupUI() {
        button = new JButton("Click me");
        add(button);
    }

    public void showButton() {
        SwingUtilities.invokeLater(() -> {
            button.setVisible(true);
        });
    }

    public static void main(String[] args) {
        ButtonExample example = new ButtonExample();
        example.showButton();
    }
}