This Java code is not addressing the core of a chat application (sending and receiving messages) however it makes a good GUI skeleton for starting such an application.

1.  import java.awt.BorderLayout;
2.  import javax.swing.JPanel;
3.  import javax.swing.JFrame;
4.  import javax.swing.JTextArea;
5.  import javax.swing.JTextField;
6.  import javax.swing.JButton;
7.  import java.awt.Dimension;
8.  import java.awt.event.*;
9.  import javax.swing.BoxLayout;
10.  
11. public class Chatroom extends JFrame {
12.  
13.         private static final long serialVersionUID = 1L;
14.  
15.         private JPanel jContentPane = null;
16.  
17.         private JTextArea jTextArea = null;
18.  
19.         private JPanel jPanel = null;
20.  
21.         private JTextField jTextField = null;
22. 
23.         private JButton jButton = null;
24. 
25.         /**
26.          * This is the default constructor
27.          */
28.         public Chatroom() {
29.                 super();
30.                initialize();
31.         }
32. 
33.         /**
34.          * This method initializes this
35.          *
36.          * @return void
37.          */
38.         private void initialize() {
39.                 this.setSize(411, 331);
40.                 this.setContentPane(getJContentPane());
41.                 this.setTitle("Chatroom");
42.         }
43.  
44.         /**
45.          * This method initializes jContentPane
46.          *
47.          * @return javax.swing.JPanel
48.          */
49.         private JPanel getJContentPane() {
50.                 if (jContentPane == null) {
51.                         jContentPane = new JPanel();
52.                         jContentPane.setLayout(new BorderLayout());
53.                         jContentPane.add(getJTextArea(), BorderLayout.CENTER);
54.                         jContentPane.add(getJPanel(), BorderLayout.SOUTH);
55.                 }
56.                 return jContentPane;
57.         }
58.  
59.         /**
60.          * This method initializes jTextArea   
61.          *      
62.          * @return javax.swing.JTextArea       
63.          */
64.         private JTextArea getJTextArea() {
65.                 if (jTextArea == null) {
66.                         jTextArea = new JTextArea();
67.                         jTextArea.setEnabled(true);
68.                         jTextArea.setEditable(false);
69.                 }
70.                 return jTextArea;
71.         }
72.  
73.         /**
74.          * This method initializes jPanel       
75.          *      
76.          * @return javax.swing.JPanel   
77.          */
78.         private JPanel getJPanel() {
79.                 if (jPanel == null) {
80.                         jPanel = new JPanel();
81.                         jPanel.setLayout(new BoxLayout(getJPanel(), BoxLayout.X_AXIS));
82.                         jPanel.setPreferredSize(new Dimension(0, 30));
83.                         jPanel.add(getJTextField(), null);
84.                         jPanel.add(getJButton(), null);
85.                 }
86.                 return jPanel;
87.         }
88.  
89.         /**
90.          * This method initializes jTextField   
91.          *      
92.          * @return javax.swing.JTextField       
93.          */
94.         private JTextField getJTextField() {
95.                 if (jTextField == null) {
96.                         jTextField = new JTextField();
97.                         jTextField.addKeyListener(new java.awt.event.KeyAdapter() {
98.                                 public void keyPressed(java.awt.event.KeyEvent e) {
99.                                         // If Enter was pressed
100.                                         if(e.getKeyCode() == 10)
101.                                         {
102.                                                 addMessage();
103.                                         }
104.                                         setTitle("Chatroom - Typing a message...");
105.                                         t.start();
106.                                 }
107.                         });
108.                 }
109.                 return jTextField;
110.         }
111.        
112.         private void addMessage()
113.         {
114.                 jTextArea.append(jTextField.getText() + "\r\n"); // TODO Auto-generated Event stub mouseClicked()
115.                 jTextField.setText("");
116.                 setTitle("Chatroom");
117.         }
118.        
119.         javax.swing.Timer t = new javax.swing.Timer(3000, new ActionListener() {
120.         public void actionPerformed(ActionEvent e) {
121.                 setTitle("Chatroom");  //  @jve:decl-index=0:
122.         }
123.      });
124.  
125.         /**
126.          * This method initializes jButton     
127.          *      
128.          * @return javax.swing.JButton 
129.          */
130.         private JButton getJButton() {
131.                 if (jButton == null) {
132.                         jButton = new JButton();
133.                         jButton.setPreferredSize(new Dimension(80, 50));
134.                         jButton.setText("SEND");
135.                         jButton.addMouseListener(new java.awt.event.MouseAdapter() {
136.                                 public void mouseClicked(java.awt.event.MouseEvent e) {
137.                                         addMessage();
138.                                 }
139.                         });
140.                 }
141.                 return jButton;
142.         }
143.  
144. }  //  @jve:decl-index=0:visual-constraint="10,10"