class created

src/ChatArea.java

-public class ChatArea {
+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);
+    }
+
+    public void addMessage(String username, String message) {
+        String sb1 = username + ": " + message;
+        append(sb1);
+    }
 }

src/ChatRoomGUI.java

-public class ChatRoomGUI {
+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;
+
+    public ChatRoomGUI() {
+        super();
+        this.setTitle(WINDOWS_TITLE);
+        this.setLayout(null);
+        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
+        this.setSize(WIDTH, HEIGHT);
+        this.setLocation(X, Y);
+        this.setVisible(true);
+        ChatArea chatBox = new ChatArea();
+        this.add(new JScrollPane(chatBox), BorderLayout.CENTER);
+    }
+
+
 }

src/Main.java

 public class Main {
 
     public static void main(String[] args) {
-        System.out.println("Hello World!");
+        //System.out.println("Hello World!");
+        //UsernameFrame usernameFrame = new UsernameFrame();
+        ChatRoomGUI chatRoomGUI = new ChatRoomGUI();
     }
+
 }

src/ParticipantsArea.java

 public class ParticipantsArea {
+
+
+    public void addNewParticipant(String username) {
+
+    }
+
+    public void removeParticipant(String username) {
+
+    }
 }

src/UsernameFrame.java

-public class UsernameFrame {
-}
+import javax.swing.*;
+import java.awt.*;
+
+public class UsernameFrame 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 UsernameFrame() 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