用Java做个单线聊天室，为什么总是接收不到对方发出的消息。跪求

用Java做个单线聊天室，为什么总是接收不到对方发出的消息。跪求高手指点
服务器端：
package HomeWork;
import javax.swing.*;
import javax.swing.border.Border;
import javax.swing.border.LineBorder;
import javax.swing.border.TitledBorder;



import java.awt.*;
import java.awt.event.*;
import java.io.BufferedReader;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.Date;

public class singlechat extends JFrame {
  JTextArea textarea,textarea1;
  //JTextField textfield;
  JButton button,button1,button2,button3,button4,button5;
  JPanel panel1 = new JPanel();
  JPanel panel2 = new JPanel();
  JPanel panel3 = new JPanel();
  JPanel panel4 = new JPanel();
  JScrollPane scrollpane;
  public DataInputStream din;
public DataOutputStream dout;  
  public Socket socket ;

  public static void main(String[] args) {
  new singlechat();
  }

  public singlechat() {
  super("聊天室");
  addWindowListener(new WindowAdapter() {
  public void windowClosing(WindowEvent e) {
  try{
  din.close();
  dout.close();
  socket.close();
  System.exit(0);
  }
  catch (IOException ex){
  System.out.println("client closing: "+ ex.toString());
  }
  }
  });
  //this.setLayout();
  Font largeFont = new Font("TimesRoman", Font.BOLD, 20);
  Border lineBorder = new LineBorder(Color.BLACK, 2);
  button = new JButton("发送");
  button1 = new JButton("老大");
  button2 = new JButton("老二");
  button3 = new JButton("老三");  
  button4 = new JButton("老四");
  button5 = new JButton("老五");
  textarea = new JTextArea(6, 30);
  textarea1 = new JTextArea(3,30);
  textarea.setForeground(Color.blue);
  textarea.setFont(largeFont);
  textarea.setBorder(lineBorder);
  textarea1.setForeground(Color.red);
  textarea1.setFont(largeFont);
  textarea1.setBorder(lineBorder);
  textarea1.setBackground(Color.cyan );
  scrollpane = new JScrollPane(textarea);
  //scrollpane.setPreferredSize(new Dimension(200, 200));
  //textfield = new JTextField(20);//textfield要先new出来
  //textfield.setForeground(Color.red);
   
  // setContentPane(panel1);
  panel1.setPreferredSize(new Dimension(400, 300));
  //panel1.setBackground(Color.white);
  // panel1.setForeground(Color.blue);
  panel1.setVisible(true);
  panel1.setBorder(new TitledBorder("显示区域"));
  panel1.setLayout(new BorderLayout());// 设置边界布局
  panel1.add(scrollpane, BorderLayout.CENTER);
  //this.add(panel1);
  // setContentPane(panel2);
   
  //panel2.setBackground(Color.white);
  //panel2.setForeground(Color.blue);
  panel2.setVisible(true);
  panel2.setPreferredSize(new Dimension(400, 100));
  panel2.setBorder(new TitledBorder("输入区域"));
  panel2.setLayout(new GridLayout(2,1,10,10));// 设置边界布局