I wanted to do a multithreaded ChatServer, which is based on telnet and I thought I got it but after I type in 1 message in telnet it gives the following error
"Exception in thread "Thread-0" java.lang.NullPointerException
at Server.sendAll(Server.java:20)
at ServerThreads.run(ServerThreads.java:33)"
I know where it causes the problem but I don't know how I can fix it specifically in my code. I think all the other stuff is working fine. This is my ServerThread Class
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.InetAddress;
import java.net.ServerSocket;
import java.net.Socket;
public class ServerThreads extends Thread {
private String prefix;
private Socket socket;
PrintWriter pw;
public ServerThreads(String prefix, Socket s){
this.prefix = prefix;
this.socket = s;
this.start();
}
public void run(){
try {
PrintWriter pw = new PrintWriter(socket.getOutputStream(),true);
BufferedReader br = new BufferedReader(new InputStreamReader(socket.getInputStream()));
Server.list.einfuegen(0, this);
pw.println("Client verbunden mit: "+prefix);
while(true){
//System.out.println("User: "+ socket.getInetAddress() + " Nachricht: " + line);
String line = br.readLine();
Server.sendAll(line, prefix);
pw.flush();
}
}catch (IOException e){
e.printStackTrace();
}
}
}
This is my Server Class
import java.io.IOException;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
public class Server {
static EinfachListe list = new EinfachListe();
static int zaehler = 1;
private int port;
ServerSocket socket;
public Server(int port) throws IOException{
this.port = port;
socket = new ServerSocket(port);
}
static public void sendAll(String s, String prefix){
for(int a = 0; a<list.getAnzahl(); a++){
((ServerThreads) (list.get(a))).pw.println(s);
}
}
public void starteServer(){
System.out.println("Der Server wurde gestartet");
while(true){
try {
Socket s = socket.accept();
//ServerThreads user = new ServerThreads("User:Anzahl Nachrichten "+zaehler++, 1000, s);
String client = "Client"+zaehler++;
new ServerThreads(client, s);
//user.start();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
I don't think that the mistake is in my LinkedList but if you think it is I can also copy the code of my LinkedList in here. Thank you for the help!
