Java实现可折叠界面

import java.awt.BorderLayout;

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.DefaultTreeModel;
import javax.swing.tree.MutableTreeNode;

public class MainClass extends JPanel {

  public static void main(String[] args) {
	
    
	MutableTreeNode root = new DefaultMutableTreeNode("QQ好友");
    MutableTreeNode aNode = new DefaultMutableTreeNode("我的好友");
    MutableTreeNode bNode = new DefaultMutableTreeNode("陌生人");
    MutableTreeNode cNode = new DefaultMutableTreeNode("黑名单");
    
    root.insert(aNode, 0);
    root.insert(bNode, 1);
    root.insert(cNode, 2);
    aNode.insert(new DefaultMutableTreeNode("friend_a"), 0);
    aNode.insert(new DefaultMutableTreeNode("friend_b"), 1);
    bNode.insert(new DefaultMutableTreeNode("stranger_a"), 0);
    bNode.insert(new DefaultMutableTreeNode("stranger_b"), 1);
    cNode.insert(new DefaultMutableTreeNode("black_a"), 0);
    cNode.insert(new DefaultMutableTreeNode("black_b"), 1);
    
    DefaultTreeModel model = new DefaultTreeModel(root);
    JTree tree = new JTree(model);

    JFrame frame = new JFrame("QQ");
	frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.add(new JScrollPane(tree),BorderLayout.NORTH);
    frame.pack();
    frame.setVisible(true);
    
  }
}
import java.awt.BorderLayout;

import javax.swi