以下是一个基本的Java socket编程案例：

服务端代码：

import java.net.*;
import java.io.*;

public class Server {
    public static void main(String[] args) throws IOException {

        ServerSocket serverSocket = null;
        try {
            serverSocket = new ServerSocket(8080);
        } catch (IOException e) {
            System.err.println("Could not listen on port: 8080.");
            System.exit(1);
        }

        Socket clientSocket = null;
        try {
            System.out.println("Waiting for connection.....");
            clientSocket = serverSocket.accept();
            System.out.println("Connection successful");
        } catch (IOException e) {
            System.err.println("Accept failed.");
            System.exit(1);
        }

        PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);
        BufferedReader in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));

        String inputLine;
        while ((inputLine = in.readLine()) != null) {
            System.out.println("Server: " + inputLine);
            out.println(inputLine);
            if (inputLine.equals("Bye."))
                break;
        }

        out.close();
        in.close();
        clientSocket.close();
        serverSocket.close();
    }
}

客户端代码：

import java.net.*;
import java.io.*;

public class Client {
    public static void main(String[] args) throws IOException {

        Socket socket = null;
        PrintWriter out = null;
        BufferedReader in = null;

        try {
            socket = new Socket("localhost", 8080);
            out = new PrintWriter(socket.getOutputStream(), true);
            in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
        } catch (UnknownHostException e) {
            System.err.println("Don't know about host: localhost.");
            System.exit(1);
        } catch (IOException e) {
            System.err.println("Couldn't get I/O for the connection to: localhost.");
            System.exit(1);
        }

        BufferedReader stdIn = new BufferedReader(new InputStreamReader(System.in));
        String userInput;

        while ((userInput = stdIn.readLine()) != null) {
            out.println(userInput);
            System.out.println("Client: " + userInput);
            if (userInput.equals("Bye."))
                break;
            System.out.println("Server: " + in.readLine());
        }

        out.close();
        in.close();
        stdIn.close();
        socket.close();
    }
}

这个案例实现了一个简单的客户端和服务端之间的通信，客户端向服务端发送一条消息，服务端将其打印后返回给客户端。如果客户端发送了 "Bye."，则结束通信。