求助程序调试出错提示 java.lang.NullPointerException

要求是服务器的Server2.java同过套接字将两个文件压缩后发送给客户端，客户端接受．

下面程序是调试服务端有问题，客户端没问题．

Server2.java
import java.io.*;
import java.net.*;
import java.util.zip.*;

public class Server2
{
    public static void main(String args[])
    {
        ServerSocket server = null;
        ServerThread thread;
        Socket you = null;
        while(true)
        {
            try
            {
                server = new ServerSocket(4331);
            }
            catch(IOException e1)
            {
                System.out.println("正在监听");
            }
            try
            {
                System.out.println("等待客户呼叫");
                you = server.accept();
                System.out.println("客户地址:"+you.getInetAddress());
            }
            catch(IOException e)
            {
                System.out.println("正在等待客户");
            }
            if(you!=null)
            {
                new ServerThread(you).start();
            }
        }
    }
}

class ServerThread extends Thread
{
    Socket socket;
    ZipOutputStream out;
    String s = null;
    ServerThread(Socket t)
    {
        socket = t;
        try
        {
            out = new ZipOutputStream(socket.getOutputStream());
        }
        catch(IOException e){}
    }
    public void run()
    {
        try
        {
            out.putNextEntry(new ZipEntry("Example.java"));
            FileInputStream reader = new FileInputStream("Example.java");
            byte b[]=new byte[1024];
            int n = -1;
            while((n=reader.read(b,0,1024))!=-1)
            {
                out.write(b, 0, n);
            }
            out.putNextEntry(new ZipEntry("E.java"));
            reader = new FileInputStream("E.java");
            n = -1;
            while((n = reader.read(b, 0, 1024))!=-1)
            {
                out.write(b, 0, n);
            }
            reader.close();
            out.close();
        }
        catch(IOException e){}
    }
}

总是提示：
java.lang.NullPointerException
    at Server2.main(Server2.java:25)
Exception in thread "main"

查了好久了，就是不知错在哪，请大家帮忙看看．

搜索更多相关主题的帖子: java lang 服务器 提示

应该是
server = new ServerSocket(4331);
这句有错吧。
ServerSocket的参数应该是Socket类型的，不能直接写成4331。把它转换成Socket应该就可以了吧。
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