[JAVA100例]076、在Applet中使用Swing

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.tree.*;
import java.io.*;
import java.net.*;
import java.util.*;
import java.applet.*;
/**
 * <p>Title: Applet中使用SWING</p>
 * <p>Description: 使用SWING的JApplet实现树功能。</p>
 * <p>Copyright: Copyright (c) 2003</p>
 * <p>Filename: PageTree.java</p>
 * @version 1.0
 */
public class PageTree extends JApplet implements TreeSelectionListener {
 DefaultMutableTreeNode[] nodeAt = new DefaultMutableTreeNode[256];
 String target = null;
 Hashtable links = new Hashtable();
 AppletContext context;
 public void init() {
  //获取Applet的内容
  context = getAppletContext();
  //定义根节点
  DefaultMutableTreeNode root = null;
  getContentPane().setLayout(new BorderLayout());
  //获取参数。定义的数据配置文件。
  String s = getParameter("file");
  if (s != null) {
   try {
    //使用URL方式打开数据文件，实现在网络上使用。
    URL url = new URL(getDocumentBase(), s);
    BufferedReader br = new BufferedReader(
     new InputStreamReader(url.openStream(), "JISAutoDetect"));
    //读取第一行数据，假如为空则不执行
    String line = br.readLine();
    if (line == null) return;
    root = new DefaultMutableTreeNode(line);
    nodeAt[0] = root;
    int level = 0;
    while ((line = br.readLine()) != null) {
     //使用“”分开数据
     StringTokenizer st = new StringTokenizer(line, "");
     String token = st.nextToken();
     int n = countSpaces(token);
     //添加节点名称
     DefaultMutableTreeNode node = new DefaultMutableTreeNode(token.trim());
     //计算节点级数
     for (int i = level + 1; i < n; i++) {
      DefaultMutableTreeNode dummy = new DefaultMutableTreeNode("");
      nodeAt[i].add(dummy);
      nodeAt[i+1] = dummy;
     }
     level = n;
     nodeAt[n].add(node);
     nodeAt[n+1] = node;
     //对“”符号后的数据进行处理
     if (st.hasMoreTokens()) {
      token = st.nextToken();
      try {
       url = new URL(token.trim());
       links.put(node, url);
      } catch (MalformedURLException ex) {
       ex.PRintStackTrace();
      }
     }
    }
   } catch (MalformedURLException e) {
    e.printStackTrace();
   } catch (IOException e) {
    e.printStackTrace();
   }
   s = getParameter("target");
   if (s != null) target = s.trim();
   JTree tree = new JTree(root);
   //添加树的选择监听
   tree.addTreeSelectionListener(this);
   JScrollPane jsp = new JScrollPane(tree);
   getContentPane().add(jsp, BorderLayout.CENTER);
  }
 }
/**
 *<br>方法说明：计算空格数
 *<br>输入参数：
 *<br>返回类型：
 */ 
 private int countSpaces(String s) {
  int n = 0;
  while (s.charAt(n) == ´ ´) {
   n++;
  }
  return n;
 }
/**
 *<br>方法说明：树选择监听实现方法
 *<br>输入参数：TreeSelectionEvent e 选择树节点事件
 *<br>返回类型：
 */ 
 public void valueChanged(TreeSelectionEvent e) {
  TreePath path = e.getPath();
  Object o = path.getLastPathComponent();
  URL url = (URL)links.get(o);
  if (url != null) {
   System.out.println(links.get(o));
   //打开连接，通知浏览器加载网页（使用浏览器打开Applet的情况下）
   context.showDocument(url);
  }
 }