Problems wait and notify

Question about the task

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Hello I read and check different examples of wait and modify ,I try different things and I really don't know what is wrong ,I need help

Let's start writing the main functionality of the Client class.

1) Add a public void run() method. It should create a helper SocketThread, wait until it establishes a connection with the server, and then in a loop, read messages from the console and send them to the server. The loop will terminate either when the client shuts down or the user enters the 'exit' command'.
To inform the main thread that the connection is established on the helper thread, use the Client object's wait() and notify() methods.

The implementation should:
a) Create a new socket thread using the getSocketThread() method.
b) Mark the created thread as a daemon. This is necessary so that the helper thread is automatically interrupted when the program exits.
c) Start the helper thread.
d) Make the current thread wait until it receives a notification from another thread.
Hint: use wait() and object level synchronization. If an exception occurs while waiting, notify the user and exit the program.
d) Once the thread receives a notification, check the value of clientConnected. If it is true, display "Connection established. To exit, enter 'exit'.". If it is false, display "An error occurred while working with the client.".
e) Read messages from the console until the client is connected. If 'exit' is entered, then exit the loop.
g) After each string is read, if the shouldSendTextFromConsole() method returns true, send the text using the sendTextMessage() method.

2) Add the public static void main(String[] args) method. It must create a new Client object and call its run() method.

Requirements:

The main() method should create a new Client object and call its run() method.
The run() method should create and start a new thread that is obtained using the getSocketThread() method.
The thread created using the getSocketThread() method should be marked as a daemon (setDaemon(true)).
After starting the new socketThread, the run() method should wait until it is awakened.
As long as the clientConnected flag is true, messages should be read from the console using the ConsoleHelper.readString() method.
If the "exit" command is entered, you should interrupt the message-reading loop.
If the shouldSentTextFromConsole() method returns true, the sendTextMessage() method should be called with the input text used as an argument.

package com.codegym.task.task30.task3008; import java.io.IOException; import java.net.ServerSocket; import java.net.Socket; import java.util.HashMap; import java.util.Map; import java.util.concurrent.ConcurrentHashMap; import java.util.logging.Handler; public class Server { private static Map<String,Connection> connectionMap; static { connectionMap = new ConcurrentHashMap<> ( ); } public static void main(String[] args) throws IOException { int port = ConsoleHelper.readInt (); java.net.ServerSocket serverSocket = new ServerSocket (port ); ConsoleHelper.writeMessage ( "Server is running"); Socket socket = null; while(true) { socket = serverSocket.accept (); Thread handler = new Handler ( socket ); handler.start (); try { }catch (Exception o) { serverSocket.close (); ConsoleHelper.writeMessage ( "Error" ); } //serverSocket.close (); } } private static class Handler extends Thread { private Socket socket; public Handler(Socket socket) { this.socket = socket; } @Override public void run() { ConsoleHelper.writeMessage ( "Connection has been established whit remote address " + socket.getRemoteSocketAddress () ); String userName = null; Connection connection = null; try { connection = new Connection ( socket ); userName = serverHandshake ( connection ); sendBroadcastMessage ( new Message ( MessageType.USER_ADDED,userName ) ); notifyUsers ( connection,userName ); serverMainLoop ( connection,userName ); connection.close (); connectionMap.remove ( userName ); sendBroadcastMessage ( new Message ( MessageType.USER_REMOVED,userName ) ); ConsoleHelper.writeMessage ( "connection is finished whit remote adress" + socket.getRemoteSocketAddress () ); }catch (Exception o){ } } private String serverHandshake(Connection connection) throws IOException,ClassNotFoundException{ while(true){ connection.send ( new Message ( MessageType.NAME_REQUEST ) ); Message answer = connection.receive (); if(answer.getType ().equals (MessageType.USER_NAME)){ String data = answer.getData (); if(data != null & (!data.isEmpty ()) & (!connectionMap.containsKey ( data ))){ connectionMap.put (data,connection ); connection.send ( new Message ( MessageType.NAME_ACCEPTED ) ); return data; }else { continue; } }else { continue; } } } private void notifyUsers(Connection connection,String userName) throws IOException{ for(ConcurrentHashMap.Entry<String,Connection> map : connectionMap.entrySet ()){ //String name = map.getKey (); // Message message = new Message ( MessageType.USER_ADDED,name ); if(!map.getKey ().equals ( userName )) { connection.send ( new Message ( MessageType.USER_ADDED,map.getKey () ) ); } } } private void serverMainLoop(Connection connection,String userName) throws IOException,ClassNotFoundException{ while(true) { // try { Message message = connection.receive (); if (message.getType ().equals ( MessageType.TEXT )) { Message newMessage = new Message ( MessageType.TEXT, userName + ": " + message.getData () ); sendBroadcastMessage ( newMessage ); } else ConsoleHelper.writeMessage ( "Error" ); // }catch (Exception o){ // } } } } public static void sendBroadcastMessage(Message message){ for(Connection c : connectionMap.values()){ try { c.send(message); } catch (IOException e) { ConsoleHelper.writeMessage("Message couldn't be sent."); } } } }

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Justin Smith

Level 41 , Greenfield, USA, United States

19 March 2022, 13:39

Unfortunately, the directions are flat-out misleading. It says to use notify(), but I passed without using it, and after I passed I checked the solution and it did not use it either. My guess is that we use notify() in the SocketThread class, which we don't fill out in this section yet. Maybe CodeGym was originally going to do that part in this lesson and they forgot to remove that piece of the instructions after they changed their mind. Other than that, I try to follow the directions in order as best I can. You'll notice that the directions do not say to set clientConnected = true. It will never get set to true with the existing code, but just leave it be for now. My guess is that that also gets set to true in the SocketThread class later. You do, however, need to use wait() and a synchronized block. The goal here is to make the execution of the run() method pause until it gets a notify from somewhere else (again, we don't end up writing the notify in this lesson, despite what it says). We have used wait(int) a lot in the past, but wait() without an argument simply waits indefinitely until it hears from notify(). So just call wait() from inside a synchronized block, and remember that, as the directions indicate, you will then need to put that in a try block to account for InterruptedException. Moving on, you have a while loop, but not the right variable in it. So this is another area where the directions are wrong. It says "Read messages from the console until the client is connected." Which of course is nonsense. "Until" should say "while." And that should make it obvious that you actually want while(clientConnected), and then fill in the loop accordingly. The errors in the directions are probably why this task is rated 1 star.