Written a simple chat software in Java using UDP, but I can't receive any messages. Please let me know what's wrong with the code.

package com.window; import javax.swing.*; import java.awt.*; import java.awt.event.MouseAdapter; import java.awt.event.MouseEvent; import java.io.IOException; import java.net.DatagramPacket; import java.net.DatagramSocket; import java.net.InetAddress; import java.util.ArrayList; import java.util.Arrays; import java.util.List; import java.util.logging.Logger; /** * Created by young on 2017/4/19. */ public class MainWindow { private JLabel lb_addIp; private JButton btn_add; private JPanel jp_qq; private JLabel lb_selectIP; private JComboBox cb_selectIP; private JTextField tf_addip; private JTextArea ta_charHistory; private JTextField tf_input; private JButton btn_submit; private JLabel lb_charHistory; private JLabel lb_message; private JTextPane tp; private String ip; private String sendMessage; private int sendport = 10023; private int receviceport = 10024; private DefaultListModel listModel = new DefaultListModel(); public String name; private List messageList = new ArrayList<>(); public MainWindow() { btn_add.addMouseListener(new MouseAdapter() { @Override public void mouseClicked(MouseEvent e) { ip = tf_addip.getText(); Object[] com = new Object[]{ip}; cb_selectIP.addItem(ip); } }); btn_submit.addMouseListener(new MouseAdapter() { Logger logger = Logger.getLogger("submit"); @Override public void mouseClicked(MouseEvent e) { if (ip == null) { lb_message.setForeground(Color.red); lb_message.setText("请输入IP。"); return; } try { InetAddress inetAddress = InetAddress.getByName(ip); if (!inetAddress.isReachable(2000)) { lb_message.setForeground(Color.red); lb_message.setText("无法链接该地址！"); return; } } catch (IOException e1) { e1.printStackTrace(); } sendMessage = tf_input.getText(); logger.info("sendMessage" + sendMessage); new Thread(() -> { send(sendMessage); lb_message.setForeground(Color.green); lb_message.setText("发送成功。"); }).start(); new Thread(() -> { receive(); }).start(); } }); } public void receive() { DatagramSocket datagramSocket = null; try { datagramSocket = new DatagramSocket(sendport, InetAddress.getByName(ip)); byte[] buf = new byte[1024]; DatagramPacket datagramPacket = new DatagramPacket(buf, buf.length); datagramSocket.receive(datagramPacket); String id = datagramPacket.getAddress().getHostAddress(); int port = datagramPacket.getPort(); byte[] date = datagramPacket.getData(); System.out.println(Arrays.toString(date)); String mes = ip + ":" + new String(date) + "\n"; //System.out.println("ip=" + id + "port=" + port); tp.setText(tp.getText() + mes); } catch (IOException e) { e.printStackTrace(); } finally { assert datagramSocket != null; datagramSocket.close(); } } public void initWindow() { JFrame frame = new JFrame("QQ"); frame.setContentPane(new MainWindow().jp_qq); frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE); frame.pack(); frame.setVisible(true); tp.setEditable(false); } public void send(String message) { DatagramSocket datagramSocket = null; try { datagramSocket = new DatagramSocket(receviceport); byte[] buf = message.getBytes(); DatagramPacket packet = new DatagramPacket(buf, buf.length, InetAddress.getByName(ip), sendport); datagramSocket.send(packet); tp.setText(tp.getText() + name + message + "\n"); } catch (IOException e) { e.printStackTrace(); } finally { datagramSocket.close(); } } }

There is a lot of code, so I put it on github
github address