如何在没有闪烁的情况下调整Swing JWindow的大小？

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

public class CustomWindow extends JWindow {
    private Image bufferImage;

    public CustomWindow() {
        setSize(400, 300);
        setLocationRelativeTo(null);
        setAlwaysOnTop(true);
        setVisible(true);
    }

    @Override
    public void paint(Graphics g) {
        if (bufferImage == null) {
            bufferImage = createImage(getWidth(), getHeight());
        }
        Graphics bufferGraphics = bufferImage.getGraphics();
        bufferGraphics.setColor(getBackground());
        bufferGraphics.fillRect(0, 0, getWidth(), getHeight());
        // 在bufferGraphics上进行其他绘制操作

        g.drawImage(bufferImage, 0, 0, null);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> {
            CustomWindow window = new CustomWindow();
            // 调整窗口大小
            window.setVisible(false);
            window.setSize(600, 400);
            window.setVisible(true);
        });
    }
}