import java.io. *; import java.net.*; import java.util. *; public class EchoServer{ public static void main(String[] args) throws IOException {new EchoServerThread().start();}} class EchoServerThread extends Thread{ protected DatagramSocket socket = null; protected BufferedReader in = null; protected boolean hasMoreWork = true; protected int number = 0;//访问计数变量 public EchoServerThread() throws IOException{ this("EchoServerThread"); } public EchoServerThread(String name) throws IOException{ super(name); socket = new DatagramSocket(4248); public void run(){ while (hasMoreWork) { try{ byte[] buf = new byte[256];//接收应答 DatagramPacket packet = new DatagramPacket(buf, buf.length); socket.receive(packet); //创建应答 String dString = null; number++; dString ="Hi!你是第"+ number + "个访问者!"; buf = dString.getBytes();//将应答发送给端口和地址为"address""port"的客户 InetAddress address = packet.getAddress(); int port = packet.getPort(); packet = new DatagramPacket(buf, buf.length, address, port); socket.send(packet); }catch (IOException e){ e.printStackTrace(); hasMoreWork = false; } } socket.close();} } }哪里出错了

代码中有几个语法错误：
1. 在 EchoServerThread 构造函数中没有关闭构造函数的大括号。
2. run() 函数中没有关闭while循环的大括号。
3. 在 run() 函数中，未在 EchoServerThread 类之前添加 public 关键字。

下面是修改后的代码：

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

public class EchoServer {
    public static void main(String[] args) throws IOException {
        new EchoServerThread().start();
    }
}

class EchoServerThread extends Thread {
    protected DatagramSocket socket = null;
    protected BufferedReader in = null;
    protected boolean hasMoreWork = true;
    protected int number = 0; // 访问计数变量

    public EchoServerThread() throws IOException {
        this("EchoServerThread");
    }

    public EchoServerThread(String name) throws IOException {
        super(name);
        socket = new DatagramSocket(4248);
    }

    public void run() {
        while (hasMoreWork) {
            try {
                byte[] buf = new byte[256]; // 接收应答
                DatagramPacket packet = new DatagramPacket(buf, buf.length);
                socket.receive(packet); // 创建应答
                String dString = null;
                number++;
                dString = "Hi!你是第" + number + "个访问者!";
                buf = dString.getBytes(); // 将应答发送给端口和地址为"address" "port"的客户
                InetAddress address = packet.getAddress();
                int port = packet.getPort();
                packet = new DatagramPacket(buf, buf.length, address, port);
                socket.send(packet);
            } catch (IOException e) {
                e.printStackTrace();
                hasMoreWork = false;
            }
        }
        socket.close();
    }
}