Java Swing - 如何在JTree中单击关键节点时从属性文件中检索值

import java.awt.BorderLayout;
import java.util.Properties;
import java.util.Set;

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JScrollPane;
import javax.swing.JTree;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.DefaultTreeModel;
import javax.swing.tree.TreePath;

public class Main extends JFrame {
  static String NOTHING_SELECTED = "<nothing selected>";
  JScrollPane treeScroll;
  JTree tree;
  DefaultTreeModel treeModel;
  DefaultMutableTreeNode root = new DefaultMutableTreeNode("GIT commands");
  JLabel descriptionLabel;

  Properties properties = new Properties();
  public Main() {
    setLayout(new BorderLayout());
    treeModel = new DefaultTreeModel(root);
    tree = new JTree(treeModel);
    treeScroll = new JScrollPane(tree);
    add(treeScroll, BorderLayout.WEST);
    
    properties.setProperty("foo1", "bar1");
    properties.setProperty("foo2", "bar2");
    properties.setProperty("foo3", "bar3");
    properties.setProperty("foo4", "bar4");

    Set<Object> keySet = properties.keySet();
    for (Object key : keySet) {
      root.add(new DefaultMutableTreeNode(key));
    }

    tree.expandPath(new TreePath(root));
    descriptionLabel = new JLabel(NOTHING_SELECTED);
    add(descriptionLabel, BorderLayout.CENTER);

    tree.addTreeSelectionListener(e->{
        DefaultMutableTreeNode selection = (DefaultMutableTreeNode) tree
            .getLastSelectedPathComponent();
        if (selection != null) {
          String key = (String) selection.getUserObject();
          String command = properties.getProperty(key);
          descriptionLabel.setText(command);
        } else {
          descriptionLabel.setText(NOTHING_SELECTED);
        }
    });
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    pack();
  }
  public static void main(String[] args) {
    new Main().setVisible(true);
  }
}