copyOnWriteArrayList

src/main/java/ChatServer.java

@@ -3,12 +3,15 @@ import java.io.IOException;
 import java.net.ServerSocket;
 import java.net.Socket;
 import java.util.List;
+import java.util.concurrent.CopyOnWriteArrayList;
 
 public class ChatServer {
 	private ServerSocket serverSocket;
 	private List<ClientHandler> clients;
 
 	public ChatServer(int port) {
+		clients = new CopyOnWriteArrayList<>();
+		
 		try {
 			serverSocket = new ServerSocket(port);
 			System.out.println("Started ChatServer on port " + port);