ClientChat.java

import java.io.*;
import java.net.*;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import static java.lang.System.out;

public class ChatClient extends JFrame implements ActionListener {

    String uname;
    PrintWriter pw;
    BufferedReader br;
    JTextArea taMessages, taUserList;
    JTextField tfInput;
    JButton btnSend, btnExit;
    Socket client;

    public ChatClient(String uname, String servername) throws Exception {
        super("Connected as: " + uname);  // set title for frame
        this.uname = uname;
        client = new Socket(servername, 18524);
        br = new BufferedReader(new InputStreamReader(client.getInputStream()));
        pw = new PrintWriter(client.getOutputStream(), true);
        pw.println(uname);  // send name to server
        //bring up the chat interface
        buildInterface();
        new MessagesThread().start();  // create thread for listening for messages
    }

    public void buildInterface() {
        btnSend = new JButton("Send");
        btnExit = new JButton("Exit");
        //chat area
        taMessages = new JTextArea();
        taMessages.setRows(10);
        taMessages.setColumns(50);
        taMessages.setEditable(false);
        //online users list
        taUserList = new JTextArea();
        taUserList.setRows(10);
        taUserList.setColumns(10);
        taUserList.setEditable(false);
        //top panel (chat area and online users list
        JScrollPane chatPanel = new JScrollPane(taMessages, JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED,
                JScrollPane.HORIZONTAL_SCROLLBAR_NEVER);
        JScrollPane onlineUsersPanel = new JScrollPane(taUserList, JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED,
                JScrollPane.HORIZONTAL_SCROLLBAR_NEVER);
        JPanel tp = new JPanel(new FlowLayout());
        tp.add(chatPanel);
        tp.add(onlineUsersPanel);
        add(tp, "Center");
        //user input field
        tfInput = new JTextField(50);
        //buttom panel (input field, send and exit)
        JPanel bp = new JPanel(new FlowLayout());
        bp.add(tfInput);
        bp.add(btnSend);
        bp.add(btnExit);
        add(bp, "South");
        btnSend.addActionListener(this);
        tfInput.addActionListener(this);//allow user to press Enter key in order to send message
        btnExit.addActionListener(this);
        setSize(500, 300);
        setVisible(true);
        pack();
    }

    @Override
    public void actionPerformed(ActionEvent evt) {
        if (evt.getSource() == btnExit) {
            pw.println("end");  // send end to server so that server know about the termination
            System.exit(0);
        } else {
            // send message to server
            pw.println(tfInput.getText());
        }
    }

    public static void main(String args[]) {

        // take username from user
        String name = JOptionPane.showInputDialog(null, "Enter your name: ", "Username",
                JOptionPane.PLAIN_MESSAGE);
        String servername = "localhost";
        try {
            new ChatClient(name, servername);
        } catch (Exception ex) {
            out.println("Unable to connect to server.\nError: " + ex.getMessage());
        }

    } // end of main

    // inner class for Messages Thread
    class MessagesThread extends Thread {

        @Override
        public void run() {
            String line;
            try {
                while (true) {
                    line = br.readLine();
                    taMessages.append(line + "\n");
                    taMessages.setCaretPosition(taMessages.getDocument().getLength());//auto scroll to last message
                } // end of while
            } catch (Exception ex) {
            }
        }
    }
} //  end of client