TCP和UDP的简单JAVA程序，从《计算机网络 自顶向下方法》中抄的，然后加了点注释。
以下是按照书打的，加了点注释，也就是我个人的理解，由于我刚出茅庐，而且这方面我感觉蛮难得，希望大家有啥意见提出来，大家一起探讨探讨。
TCP客户端程序代码。
import java.io.BufferedReader;import java.io.DataOutputStream;import java.io.IOException;import java.io.InputStreamReader;import java.net.Socket;import java.net.UnknownHostException;public class TCPClient {/** * @param args * @throws Exception * @throws UnknownHostException * TCP套接字由，源IP地址，源端口号，目标IP地址，目标端口号组成的。 */public static void main(String[] args) throws UnknownHostException, Exception {// TODO Auto-generated method stubString sentence;String modifiedSentence;BufferedReader inFromUser = new BufferedReader(new InputStreamReader(System.in));// 获取键盘输入的数据Socket clientSocket = new Socket("192.168.1.3", 6789);// 建立连接时传入IP地址和端口号，TCP是可靠的连接。DataOutputStream outToServer = new DataOutputStream(clientSocket.getOutputStream());BufferedReader inFromServer = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));sentence = inFromUser.readLine();outToServer.writeBytes(sentence + '\n');modifiedSentence = inFromServer.readLine();System.out.println("From Server: " + modifiedSentence);clientSocket.close();}}import java.io.IOException;import java.net.DatagramPacket;import java.net.DatagramSocket;import java.net.InetAddress;import java.net.SocketException;public class UDPServer {/** * @param args * @throws IOException * * 没有握手请求了。 */public static void main(String[] args) throws IOException {// TODO Auto-generated method stubDatagramSocket serverSocket = new DatagramSocket(9876);byte[] receiveData = new byte[1024];byte[] sendData = new byte[1024];while(true){DatagramPacket receivePacket = new DatagramPacket(receiveData,receiveData.length);serverSocket.receive(receivePacket);String sentence = new String(receivePacket.getData());InetAddress IPAddress = receivePacket.getAddress();int port = receivePacket.getPort();String capitalizedSentence = sentence.toUpperCase();sendData = capitalizedSentence.getBytes();DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, IPAddress, port);serverSocket.send(sendPacket);}}}