Socket network communication caught an IOException exception print connection error, do not understand why?

topic description

Why is there an error in the connection between the server and the client?

I want to access the server through multithreading, using socket, but.
Server
import java.io.*;
import java.net.*;

class server implements Runnable
{

ServerSocket s_socket;
Socket c_socket;
DataInputStream in=null;
DataOutputStream out=null;
InputStream in_data;
OutputStream out_data;
int i=0;
server(){
    try {
        s_socket=new ServerSocket(7063);
        while(true) {
            c_socket=s_socket.accept();
            Thread t=new Thread(this);
            t.start();
            iPP;
        }
    }
    catch(IOException e) {
        System.out.println("");
    }
}
public void run() {
    try {
        while(true) {
            in_data=c_socket.getInputStream();
            out_data=c_socket.getOutputStream();
            in=new DataInputStream(in_data);
            out=new DataOutputStream(out_data);
            out.writeUTF("hello,");
            String s=in.readUTF();
            if(s.equals("end"))
            {
                in.close();
                out.close();
                c_socket.close();
            }
            System.out.println(""+i+":"+s+"\n");
            Thread.sleep(200);
        }
    }
    catch(IOException e) {System.out.println("");}
    catch(Exception e_) {System.out.println("");}
}

}



:
import java.io.*;
import java.net.*;

public class 9_10 {

    public static void main(String[] args) throws UnknownHostException, IOException {
        int i=0;
        DataInputStream in=null;
        DataOutputStream out=null;
        Socket c_socket;
        c_socket=new Socket("100.68.233.237",7063);
        try {
            InputStream in_data=c_socket.getInputStream();
            OutputStream out_data=c_socket.getOutputStream();
            in=new DataInputStream(in_data);
            out=new DataOutputStream(out_data);
        }
        catch(IOException e) {System.out.println("");}
        try {
            String s=""+in.readUTF();
            System.out.println(s);
            if(i>10) {
                out.writeUTF("end");
                in.close();
                out.close();
                c_socket.close();
            }
            else {
                out.writeUTF("I am client");
                iPP;
            }
        }
        catch(IOException e) {
            System.out.println("");
        }
    }

}



Mar.08,2022
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