java - Modifying a server to allow multiple clients to connect concurrently -

so i've created server , client previous part of assignment, have extend/modify server can handle multiple clients concurrently. know have along lines of

server server1 = new server();  thread thread = new thread(server1);  thread.start(); 

and have class server implement runnable.

but lecturers notes on multi-threading not clear , have been starring @ part of question long time , have got no where.

below code have written 1 client @ time connect server. appreciated.

server.java

public class server {      arraylist<string> tokens = new arraylist<string>();      private socket s;     private scanner in;     private printwriter out;      public static void main(string[] args) throws ioexception {         serversocket server = new serversocket(1234);         server serverinstance = new server();         system.out.println("server running. waiting client connect...");         while (true) {             serverinstance.s = server.accept();             system.out.println("client connected");             serverinstance.run();             system.out.println("client disconnected. waiting new client connect...");         }     }      public void start() {         system.out.println("starting " + threadname);         if (t == null) {             t = new thread(this, threadname);             t.start();         }     }      public void run() {         try {             try {                 in = new scanner(s.getinputstream());                 out = new printwriter(s.getoutputstream());                 doservice(); // actual service             }             {                 s.close();             }         }         catch (ioexception e) {             system.err.println(e);         }     }      public void doservice() throws ioexception {         while (true) {             if (!in.hasnext())                 return;             string request = in.next();             system.out.println("request received: " + request);             // (...) test type of request here (not implemented)             request(request);         }     }      public void request(string request) {          string amountstr = in.next();         if (request.startswith("submit")) {             if (tokens.size() < 10) {                 tokens.add(amountstr);                 system.out.println("token added");                 out.println("ok");             }             else {                 system.err.println("error");                 out.println("error");             }         }         else if (request.startswith("remove")) {             if (tokens.contains(amountstr)) {                 tokens.remove(amountstr);                 system.out.println("tokens removed");                 out.println("ok");             }             else {                 system.err.println("error");                 out.println("error");             }          }         else if (request.equals("quit")) {             system.err.println("program ended");             out.println("program ended");         }          tokens.sort(null);         system.out.println(tokens);         out.flush();     } } 

client.java

public class client {     public static void main(string[] args) throws ioexception {          socket s = new socket("localhost", 1234);          inputstream instream = s.getinputstream();          outputstream outstream = s.getoutputstream();          scanner in = new scanner(instream);          printwriter out = new printwriter(outstream);          string request = "submit hello \n";          out.print(request);          out.flush();          string response = in.nextline();          system.out.println("token: " + response);          s.close();     } } 

what trying duplicate rmi has been doing decades. java open source can @ how rmi works , learn there. can on internet myriad examples of multi threaded servers with/without rmi.