Java NoClassDefFoundError

Question

在这里，我正在下载网页源代码，然后将其存储在文本文件中。然后我读取该文件并将其与正则表达式匹配以搜索特定字符串。

没有编译器错误。

Exception in thread "main" java.lang.NoClassDefFoundError: java/lang/CharSequence

谁能告诉我我错在哪里。

java version "1.3.1_01"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.3.1_01)
Java HotSpot(TM) Client VM (build 1.3.1_01, mixed mode)

 

import java.io.*;
import java.net.*;
import java.lang.*;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class WebDownload
{
  public void getWebsite()
   {
     try{
    URL url=new URL("www.gmail.com");// any URL can be given
    URLConnection urlc=url.openConnection();
    BufferedInputStream buffer=new BufferedInputStream(urlc.getInputStream());
    StringBuffer builder=new StringBuffer();
    int byteRead;
    FileOutputStream fout;
    StringBuffer contentBuf = new StringBuffer();

    while((byteRead=buffer.read())  !=-1)
    {

        builder.append((char)byteRead);



         fout = new FileOutputStream ("myfile3.txt");


            new PrintStream(fout).println (builder.toString());

            fout.close();   


    } 
    BufferedReader in = new BufferedReader(new FileReader("myfile3.txt"));
String buf = null;
while ((buf = in.readLine()) != null) {
 contentBuf.append(buf);contentBuf.append("\n");
}
in.close();
Pattern p = Pattern.compile("<div class=\"summarycount\">([^<]*)</div>");
Matcher matcher = p.matcher(contentBuf);
 if(matcher.find())
     {
    System.out.println(matcher.group(1));
     }
  else

     System.out.println("could not find");
  }
     catch(MalformedURLException ex) {
    ex.printStackTrace();
    }
    catch(IOException ex){
      ex.printStackTrace();
     }



  }
  public static void main(String [] args)
   {
     WebDownload web=new WebDownload();
   web.getWebsite();
  }
}

Answer 1

请注意，您通常可以引用 javadoc 来确定 API 在您使用的 Java 版本中是否可用。例如，javadoc for CharSequence指出“自:1.4”。

我通常会保留一个指向 latest released API javadocs 的链接易于访问。