import java.io.IOException;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.Random;
import java.util.Scanner;

public class ServerDemo {
 private int flag;

 public void server() throws IOException {
  //創建一個服務器
  System.out.println("服務端啟動，等待客戶端連接。。。");
  PrintWriter out = null;
  Scanner getClient = null;
  ServerSocket server = null;
  Socket client = null;
  this.setFlag();
  try {
   server = new ServerSocket(6666);
   //創建一個接收連接客戶端的對象
   client = server.accept();
   System.out.println(client.getInetAddress() + " 已成功連接到此臺服務器上。");
   //字符輸出流
   out = new PrintWriter(client.getOutputStream()); //向客戶端發送數據
   out.println("歡迎來到猜數字小游戲（1-100）！！！");
   out.flush();//將緩沖流中的數據全部輸出
   getClient = new Scanner(client.getInputStream()); //接收客戶端發送的數據
   //阻塞等待客戶端發送消息過來
   while (getClient.hasNextLine()) {
    String returnMsg = null;
    String tmp = getClient.nextLine();
    if ("e".equals(tmp)) {
     break;
    } else if ("c".equals(tmp)) {
     returnMsg = "歡迎來到新一輪的猜數字小游戲（1-100）！！！";
     this.setFlag();
    } else {
     int clientInput = Integer.parseInt(tmp);

     if (clientInput > flag) {
      returnMsg = "你輸入的數字大了！！！";
     } else if (clientInput < flag) {
      returnMsg = "你輸入的數字小了！！！";
     } else {
      returnMsg = "恭喜你，猜中了！！！繼續（輸入c）,退出（輸入e）";
     }
    }
    out.println(returnMsg); //向客戶端發送數據
    out.flush();
   }
  } catch (IOException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  } finally {
   out.close();
   getClient.close();
   server.close();
  }
 }

 // 生成隨機數字
 public void setFlag() {
  Random r = new Random();
  flag = r.nextInt(100);
  System.out.println("猜數字小游戲答案：flag = " + flag);
 }

 public static void main(String[] args) throws IOException {
  new ServerDemo().server();
 }
}

import java.io.IOException;
import java.io.PrintWriter;
import java.net.Socket;
import java.util.Scanner;

public class ClientDemo {

 public void client() throws IOException {
  System.out.println("正在向服務器請求連接。。。");
  Socket client = null;
  Scanner getKey = null;
  Scanner getServer = null;
  PrintWriter out = null;
  try {
   client = new Socket("127.0.0.1", 6666);
   getServer = new Scanner(client.getInputStream());
   System.out.println(getServer.nextLine());
   out = new PrintWriter(client.getOutputStream());
   System.out.print("請輸入數字：");
   //先讀取鍵盤錄入方可向服務端發送消息
   getKey = new Scanner(System.in);
   while (getKey.hasNextLine()) {
    //寫到服務端的的控制臺
    out.println(getKey.nextLine());
    out.flush();
    try {
     System.out.println("提示消息：" + getServer.nextLine());
     System.out.print("請輸入數字：");
    } catch (Exception e) {
     System.out.print("游戲結束！！！");
     break;
    }
    //阻塞等待接收服務端的消息
   }
  } catch (Exception e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  } finally {
   getKey.close();
   getServer.close();
   out.close();
   client.close();
  }

 }

 public static void main(String[] args) throws IOException {
  new ClientDemo().client();
 }
}