请教关于树的问题

比如写了有关树的结构：
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.*;

public class Tree{
public Tree(){
JFrame f=new JFrame("TreeText");
Container contentPane=f.getContentPane();

String[] s1={"1","2","3"};  
String[] s2={"4","5"};
String[] s3={"6","7","8"};

Hashtable hashtable1=new Hashtable();
Hashtable hashtable2=new Hashtable();
hashtable1.put("A",s1);
hashtable1.put("B",s2);
hashtable1.put("C",hashtable2);
hashtable2.put("D",s3);

/**定义widnows界面**/
JTree tree=new JTree(hashtable1);
JScrollPane scrollPane=new JScrollPane();
scrollPane.setViewportView(tree);
  contentPane.add(scrollPane);
  f.pack();
  f.setVisible(true);
  f.addWindowListener(new WindowAdapter(){
     public void windowClosing(WindowEvent e){
     System.exit(0);  
     }
  });
}   
public static void main(String[] args){
   new Tree();
}
}
想通过选择树的节点打开一个文件，并将文件的内容显示在一个文本框里！可否告诉我有关代码？非常感谢！
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http://java.sun.com/docs/books/tutorial/uiswing/components/tree

see this link above.
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非常感谢！
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这个还真不明白
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