Client doesn't process commands sent from server. Java

Question

My client doesn't process commands sent from server, but my server can proces commands that client sends. If I run my client in debug than thread "in" is waiting for input string and command proceesed.
I reduced my code for easy reading.

Server:

public class Server extends Thread{

    BufferedReader in;
    PrintWriter out;
    ServerSocket server;
    Socket client = null;
    Frame frame;

Server() throws IOException{
    frame = new Frame();
    try {
        server = new ServerSocket(4444);
        frame.textAreaForServer.append("Welcome to server side!\n");
    } catch (IOException e) {
        frame.textAreaForServer.append("Couldn't listen to port 4444\n");
        System.exit(-1);
    }
    addListenerOnTextField();
    this.start();
}

private void clearVector(){
    frame.textAreaForServer.append("-clr\n");
    try {
        //send message for client
        out.println("-clr");
        frame.textAreaForServer.append("Vector is cleared\n");
    } catch (NullPointerException e1) {
        frame.textAreaForServer.append("It's impossible to perform!\n");
    }
}

public void run(){
    while (true) {
        try {
             //connection to client
            if (client == null) {
                frame.textAreaForServer.append("Waiting for client connection...\n");
                client = server.accept();
                in = new BufferedReader(new InputStreamReader(client.getInputStream()));
                out = new PrintWriter(client.getOutputStream(), true);
                frame.textAreaForServer.append("Client connected\n");              
            }
        } catch (IOException e) {
            frame.textAreaForServer.append("Can't accept\n");
            System.exit(-1);
        }            
    }
}

Client:

public class Client extends Thread{

    Socket fromserver = null;
    BufferedReader in = null;
    PrintWriter out;
    ControlPanel controlPanel;

    Client(ControlPanel controlPanel1) throws IOException {
        controlPanel = controlPanel1;
        addListenerOnTextField();
        this.start();
    }

    //connection to server
    private void connect(ControlPanel controlPanel) {
        controlPanel.textAreaForClient.append("-ct\n");
        if (fromserver == null) {
            controlPanel.textAreaForClient.append("Connecting to localhost...\n");
            try {
                fromserver = new Socket("localhost", 4444);
                in = new BufferedReader(new InputStreamReader(fromserver.getInputStream()));
                out = new PrintWriter(fromserver.getOutputStream(), true);
            } catch (IOException e1) {
                controlPanel.textAreaForClient.append("Server is not available!\n");
            }
        } else {
            controlPanel.textAreaForClient.append("Already connected\n");
        }
    }

    public void run() {
    while (true) {
        //here the -clr command sent from server should be proceeded, but it doesn't
        try {
            switch (in.readLine()) {
                case "-clr": {
                    VectorOfThreads.getInstance().getVectorOfThreads().removeAllElements();
                    controlPanel.textAreaForClient.append("Vector is cleared\n");
                    break;
                }
            }
        } catch (IOException e) {
           e.printStackTrace();
        }
    }
}

}

Answer 1

It seems that in client class you forgot to connect to server before reading any Input Stream. And furthermore you didn't call the ClearVector after creating output Stream in Server thread.

I have implemented a very basic Server/Client program based on your code. and it works fine:

Server class:

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.logging.Level;
import java.util.logging.Logger;
import jdk.internal.org.objectweb.asm.tree.analysis.Frame;

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
/**
 *
 * @author Emad
 */
public class Server extends Thread {

    BufferedReader in;
    PrintWriter out;
    ServerSocket server;
    Socket client = null;
    Frame frame;

    Server() throws IOException {
        try {
            server = new ServerSocket(4444);
            System.out.println("Welcome to server side. listening on port 4444");
        } catch (IOException e) {
            System.out.println("Couldn't listen to port 4444\\n");
            System.exit(-1);
        }
        this.start();
    }

    private void clearVector() {
        System.out.println(" -clr command send\n");
        try {
            //send message for client
            out.println("-clr");
            System.out.println("Vector is cleared\n");
        } catch (NullPointerException e1) {
            System.out.println("It's impossible to perform\n");
        }
    }

    public void run() {
        while (true) {
            try {
                //connection to client
                if (client == null) {
                    System.out.println("Waiting for client connection...\\n");
                    client = server.accept();
                    in = new BufferedReader(new InputStreamReader(client.getInputStream()));
                    out = new PrintWriter(client.getOutputStream(), true);
                    clearVector();
                    System.out.println("Client Connected!");
                }
            } catch (IOException e) {
                System.out.println("Can't accept.\n");
                System.exit(-1);
            }
        }
    }

    public static void main(String args[])
    {
        try {
            Server serverInstance = new Server();
        } catch (IOException ex) {
            System.out.println("Exception");
            Logger.getLogger(Server.class.getName()).log(Level.SEVERE, null, ex);
        }
    }
}

Client class:

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;
import java.util.logging.Level;
import java.util.logging.Logger;

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
/**
 *
 * @author Emad
 */
public class Client extends Thread {

    Socket fromserver = null;
    BufferedReader in = null;
    PrintWriter out;

    Client() throws IOException {
        this.start();
    }

    //connection to server
    private void connect() {
        System.out.println("-ct\n");
        if (fromserver == null) {
            System.out.println("Connecting to localhost...\n");
            try {
                fromserver = new Socket("localhost", 4444);
                in = new BufferedReader(new InputStreamReader(fromserver.getInputStream()));
                out = new PrintWriter(fromserver.getOutputStream(), true);
            } catch (IOException e1) {
                System.out.println("Server is not available!\n");
            }
        } else {
            System.out.println("Already connected\n");
        }
    }

    public void run() {
        connect();
        while (true) {
            //here the -clr command sent from server should be proceeded, but it doesn't
            try {
                switch (in.readLine()) {
                    case "-clr": {
                        System.out.println("Vector is cleared\n");
                        break;
                    }
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
    public static void main(String args[])
    {
        try {
            Client clientInstance = new Client();
        } catch (IOException ex) {
            System.out.println("Error in instanciating client");
        }
    }
}