VERY EVIL INDEED

src/ChatArea.java

+import javax.swing.*;
+
+public class ChatArea extends JTextArea {
+    private static final int ROWS = 10, COLUMNS = 30;
+
+    public ChatArea() {
+
+        super(ROWS, COLUMNS);
+        this.setEditable(false);
+        this.setLineWrap(true);
+        this.setVisible(true);
+    }
+
+    public void addMessage(String name, String message)
+    {
+        this.append(name + " : " + message + "\n");
+    }
+}
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src/ChatRoomGUI.java

+import javax.swing.*;
+import java.awt.*;
+
+public class ChatRoomGUI extends JFrame {
+    private final String WINDOWS_TITLE = "AUT Chat Room";
+    private final int WIDTH = 500, HEIGHT = 500;
+    private final int X = 100, Y = 100;
+    ChatArea chatArea;
+    MessageArea messageArea;
+    ParticipantsArea participantsArea;
+
+    public ChatRoomGUI() {
+        super();
+        this.setLayout(new BorderLayout());
+        this.setTitle(WINDOWS_TITLE);
+        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
+        this.setSize(WIDTH, HEIGHT);
+        this.setLocation(X, Y);
+        chatArea = new ChatArea();
+        this.add(new JScrollPane(chatArea), BorderLayout.CENTER);
+        messageArea = new MessageArea();
+        this.add(messageArea, BorderLayout.PAGE_END);
+        participantsArea = new ParticipantsArea();
+        this.add(new JScrollPane(participantsArea), BorderLayout.WEST);
+        this.setVisible(true);
+    }
+
+    public void addNewMessage(String name, String message)
+    {
+        this.chatArea.addMessage(name, message);
+    }
+
+    public void addNewParticipant(String name)
+    {
+        this.participantsArea.addNewParticipant(name);
+    }
+
+    public void removeNewParticipant(String name)
+    {
+        this.participantsArea.removeParticipant(name);
+    }
+}
\ No newline at end of file

src/Main.java

+public class Main {
+    public static void main(String[] args) {
+        ChatRoomGUI chatRoomGUI = new ChatRoomGUI();
+        NameFrame nameFrame = new NameFrame();
+        chatRoomGUI.addNewParticipant("ROHAM");
+        chatRoomGUI.addNewMessage("ROHAM", "SALAM");
+        chatRoomGUI.addNewParticipant("AMIRHOSSEIN");
+        chatRoomGUI.addNewMessage("AMIRHOSSEIN", "SALAM");
+        chatRoomGUI.addNewParticipant("GHOLI");
+        chatRoomGUI.removeNewParticipant("GHOLI");
+    }
+}

src/MessageArea.java

+import javax.swing.*;
+import java.awt.*;
+
+public class MessageArea extends JPanel{
+    JTextField textField;
+    JButton btn;
+
+    public MessageArea() throws HeadlessException {
+        super();
+        this.setLayout(new BorderLayout());
+        textField = new JTextField();
+        textField.setEditable(true);
+        add(textField, BorderLayout.CENTER);
+        btn = new JButton("SEND");
+        add(btn, BorderLayout.EAST);
+        setVisible(true);
+    }
+}

src/NameFrame.java

+import javax.swing.*;
+import java.awt.*;
+
+public class NameFrame extends JFrame {
+    private static final String BTN_TXT = " Start Chatting ...";
+    private static final String LABEL_TXT = " Choose Your UserName  ";
+    private static final int WIDTH = 300, HEIGHT = 100;
+    JTextField textField;
+    JButton btn;
+
+    public NameFrame() throws HeadlessException {
+        super();
+        this.setLayout(new BorderLayout());
+        JLabel label = new JLabel("Choose Your UserName");
+        add(label, BorderLayout.PAGE_START);
+        textField = new JTextField();
+        add(textField, BorderLayout.CENTER);
+        btn = new JButton(LABEL_TXT);
+        add(btn, BorderLayout.PAGE_END);
+        setSize(WIDTH, HEIGHT);
+        setVisible(true);
+    }
+}
\ No newline at end of file

src/ParticipantsArea.java

+import javax.swing.*;
+import java.awt.*;
+import java.util.ArrayList;
+
+public class ParticipantsArea extends JPanel {
+    private final int ROW = 20, COLUMN = 1;
+    DefaultListModel<String> model;
+    JList<String> list;
+
+    public ParticipantsArea() throws HeadlessException {
+        super();
+        GridLayout g = new GridLayout(20, 1);
+        this.setLayout(g);
+        JLabel label = new JLabel("Online Users");
+        this.add(label);
+        this.model= new DefaultListModel();
+        this.list = new JList(model);
+        this.add(list);
+        this.setVisible(true);
+    }
+
+    public void addNewParticipant(String name)
+    {
+        if (!this.model.contains(name)) {
+            this.model.addElement(name);
+        }
+    }
+
+    public void removeParticipant(String name)
+    {
+        if (this.model.contains(name)) {
+            this.model.removeElement(name);
+        }
+    }
+}