Java Swing - 如何显示JTree setSelectionPaths的玻璃窗格

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.event.MouseWheelListener;

import javax.swing.Box;
import javax.swing.BoxLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTree;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.TreePath;

public class Main extends Box {
  JPanel glassPane = new JPanel() {
    public void paintComponent(Graphics g) {
      g.setColor(new Color(0, 0, 0, 80));
      g.fillRect(0, 0, getWidth(), getHeight());
      g.setColor(Color.white);
      g.setFont(g.getFont().deriveFont(18f).deriveFont(Font.BOLD));
      g.drawString("Processing...", getWidth() - 100, getHeight() - 10);
    }
  };

  public Main() {
    super(BoxLayout.Y_AXIS);
    glassPane.setOpaque(false);
    DefaultMutableTreeNode root = new DefaultMutableTreeNode("Root");
    for (int i = 0; i < 14000; i++) {
      DefaultMutableTreeNode node = new DefaultMutableTreeNode("Root" + i);
      node.add(new DefaultMutableTreeNode("Child" + i));
      root.add(node);
    }

    final JTree tree = new JTree(root);
    tree.setRootVisible(false);
    final JScrollPane pane = new JScrollPane(tree);
    add(pane);

    JButton button = new JButton("Expand");
    button.addActionListener(e-> {
        Thread t = new Thread(new Runnable() {
          @Override
          public void run() {
            try {
              Thread.sleep(2000);
            } catch (InterruptedException e) {
              e.printStackTrace();
            }
            TreePath[] paths = tree.getSelectionPaths();
            if(paths== null || paths.length == 0){
              glassPane.setVisible(false);
              return;
            }
            tree.setSelectionPath(paths[0]);
            
            for (int i = 0; i < paths.length; i++) {
              tree.expandPath(paths[i]);
            }
            glassPane.setVisible(false);
          }
        });
        getRootPane().setGlassPane(glassPane);
        glassPane.setVisible(true);
        t.start();
    });
    add(button);
    glassPane.addMouseWheelListener(e-> {
        for (MouseWheelListener mwl : pane.getMouseWheelListeners()) {
          mwl.mouseWheelMoved(e);
        }
    });
  }

  public static void main(String[] args) {
    JFrame frame = new JFrame();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setContentPane(new Main());
    frame.pack();
    frame.setVisible(true);
  }

}