在Java中，使用Socket編程實現雙向通信需要創建兩個線程，一個用于客戶端發送數據，另一個用于服務器接收數據。以下是一個簡單的示例，展示了如何使用Java Socket實現雙向通信。

1. 服務器端代碼（Server.java）：

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

public class Server {
    public static void main(String[] args) throws IOException {
        int port = 12345;
        ServerSocket serverSocket = new ServerSocket(port);
        System.out.println("Server is listening on port " + port);

        Socket socket = serverSocket.accept();
        System.out.println("Client connected");

        // 創建兩個線程，分別用于讀取客戶端發送的數據和向客戶端發送數據
        Thread readerThread = new Thread(new ClientReader(socket));
        Thread writerThread = new Thread(new ClientWriter(socket));

        readerThread.start();
        writerThread.start();
    }
}

class ClientReader implements Runnable {
    private Socket socket;

    public ClientReader(Socket socket) {
        this.socket = socket;
    }

    @Override
    public void run() {
        try (BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()))) {
            String inputLine;
            while ((inputLine = in.readLine()) != null) {
                System.out.println("Received from client: " + inputLine);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

class ClientWriter implements Runnable {
    private Socket socket;

    public ClientWriter(Socket socket) {
        this.socket = socket;
    }

    @Override
    public void run() {
        try (PrintWriter out = new PrintWriter(socket.getOutputStream(), true)) {
            String response;
            while ((response = "Server response: ".readLine()) != null) {
                out.println(response);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

2. 客戶端代碼（Client.java）：

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

public class Client {
    public static void main(String[] args) throws IOException {
        String serverAddress = "localhost";
        int port = 12345;

        Socket socket = new Socket(serverAddress, port);
        System.out.println("Connected to server");

        // 創建兩個線程，分別用于向服務器發送數據和接收服務器的響應
        Thread senderThread = new Thread(new ServerSender(socket));
        Thread receiverThread = new Thread(new ServerReceiver(socket));

        senderThread.start();
        receiverThread.start();
    }
}

class ServerSender implements Runnable {
    private Socket socket;

    public ServerSender(Socket socket) {
        this.socket = socket;
    }

    @Override
    public void run() {
        try (PrintWriter out = new PrintWriter(socket.getOutputStream(), true)) {
            String message;
            while ((message = "Client message: ".readLine()) != null) {
                out.println(message);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

class ServerReceiver implements Runnable {
    private Socket socket;

    public ServerReceiver(Socket socket) {
        this.socket = socket;
    }

    @Override
    public void run() {
        try (BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()))) {
            String inputLine;
            while ((inputLine = in.readLine()) != null) {
                System.out.println("Received from server: " + inputLine);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

在這個示例中，服務器監聽指定端口（例如12345），當客戶端連接到服務器時，服務器會創建兩個線程，一個用于讀取客戶端發送的數據，另一個用于向客戶端發送數據。客戶端也創建了兩個線程，一個用于向服務器發送數據，另一個用于接收服務器的響應。這樣，客戶端和服務器就可以通過這兩個線程實現雙向通信。