import javax.swing.*;
import java.awt.*;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;

final public class ClientFrame extends JFrame
{
    private String name;

    private JList<String> chat;
    private DefaultListModel<String> chatModel;
    private JTextField textField;
    private JButton send;

    private Socket socket;
    private PrintWriter out;
    private BufferedReader in;

    public ClientFrame() throws IOException
    {
        super("chat");

        socket = new Socket("127.0.0.1",8888);
        out = new PrintWriter(socket.getOutputStream(), true);
        in = new BufferedReader(new InputStreamReader(socket.getInputStream()));

        chatModel = new DefaultListModel<>();
        chat = new JList<>(chatModel);
        this.add(new JScrollPane(chat));

        name = JOptionPane.showInputDialog(this,"Enter your name","Start", JOptionPane.INFORMATION_MESSAGE);
        out.println(name);
        while(in.readLine().equals("already_chosen"))
        {
            JOptionPane.showMessageDialog(this,"Somebody has already chosen this name or this name is incorrect","Warning",JOptionPane.WARNING_MESSAGE);
            name = JOptionPane.showInputDialog(this,"Enter your name","Start", JOptionPane.INFORMATION_MESSAGE);
            out.println(name);
        }
        out.println(name + " has entered the chat");

        textField = new JTextField(30);
        send = new JButton("Send");
        send.addActionListener(e -> {
            String message = getMessage();
            if(!message.equals(""))
            {
                out.println(message);
            }
          });

        JPanel sendingPanel = new JPanel();
        sendingPanel.setLayout(new FlowLayout());
        sendingPanel.add(textField);
        sendingPanel.add(send);
        this.add(sendingPanel,BorderLayout.SOUTH);

        this.setVisible(true);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setFocusable(true);
        this.setBounds(0,0,700,800);
        this.setResizable(false);

    }

    private String getMessage()
    {
        String message = textField.getText();
        textField.setText("");
        return name + " : " + message;
    }

    public static void main(String[] args) throws IOException
    {
        ClientFrame client = new ClientFrame();
        String fromServer;
        while ((fromServer = client.in.readLine()) != null)
        {
            client.chatModel.addElement(fromServer);
        }
    }


//===========================================================================================================


import java.net.*;
import java.io.*;
import java.util.LinkedList;
import java.util.TreeSet;

final public class MultiServerThread extends Thread
{
    private Socket socket = null;
    private PrintWriter out;
    private BufferedReader in;
    private LinkedList<MultiServerThread> listOfThreads;
    private static TreeSet<String> setOfNames;

    public MultiServerThread(Socket socket, LinkedList<MultiServerThread> listOfThreads, TreeSet<String> setOfNames)
    {
        this.socket = socket;
        this.listOfThreads = listOfThreads;
        this.setOfNames = setOfNames;
    }

    @Override
    public void run()
    {
        try
        {
            out = new PrintWriter(socket.getOutputStream(), true);
            in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            String inputLine, outputLine;
            inputLine = in.readLine();
            while(setOfNames.contains(inputLine) || inputLine.equals(""))
            {
                out.println("already_chosen");
                inputLine = in.readLine();
            }
            out.println(inputLine);
            setOfNames.add(inputLine);

            while((inputLine = in.readLine()) != null)
            {
                outputLine = inputLine;
                for (MultiServerThread thread : listOfThreads)
                {
                    thread.out.println(outputLine);
                }
            }
            socket.close();
        }
        catch (IOException e)
        {
            e.printStackTrace();
        }
    }
}

//===============================================================================

import java.net.*;
import java.io.*;
import java.util.LinkedList;
import java.util.TreeSet;

final public class MultiAcceptingServer
{

    private static LinkedList<MultiServerThread> listOfThreads = new LinkedList<>();
    private static TreeSet<String> setOfNames = new TreeSet<>();

    public static void main(String[] args)
    {
        int portNumber = 8888;
        boolean isListening = true;
        try(ServerSocket serverSocket = new ServerSocket(portNumber))
        {
            while(isListening)
            {
                MultiServerThread newThread = new MultiServerThread(serverSocket.accept(),listOfThreads,setOfNames);
                listOfThreads.add(newThread);
                newThread.start();
            }
        }
        catch (IOException e)
        {
            e.printStackTrace();
            System.exit(1);
        }
    }
}