Java TCP if语句

对于这个应用程序，用户发出一个命令，服务器返回一个回复。由于某种原因，

if

语句不工作，并且对于它运行的每个输入，

sentance=“Unknown Command”+“\n”。我想知道我做错了什么

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

// SERVER

class StartingPoint {
    public static void main(String argv[]) throws Exception{

        double srvversion = 0.1;
        double cliversion = 0.1;

        String clientSentence;
        String sentance = null;
        String capitalizedSentence;

        //Commands cmds = new Commands();

        ServerSocket welcomeSocket = new ServerSocket(6789);
        System.out.println("Server Started");
        while (true) {

            Socket connectionSocket = welcomeSocket.accept();
            BufferedReader inFromClient = new BufferedReader(
                    new InputStreamReader(connectionSocket.getInputStream()));
            DataOutputStream outToClient = new DataOutputStream(
                    connectionSocket.getOutputStream());
            clientSentence = inFromClient.readLine();
            System.out.println("Received: " + clientSentence);
            capitalizedSentence = clientSentence.toUpperCase();


            if(capitalizedSentence == "VERSION"){
                sentance = "Current Server Version: " + srvversion
                        + " | Current Client Version: " + cliversion + '\n';
            }else{
                sentance = "Unknown Command" + '\n';
            }

            outToClient.writeBytes(sentance);
            System.out.println("Sent: " + sentance);
        }
    }
        }

您应该使用.equals（）方法来比较字符串，而不是使用==

改变

  if(capitalizedSentence == "VERSION"){

到

要比较字符串，必须使用
.equals（）
方法，如下所示：

String str1;
String str2;

if (str1.equals(str2)) // do something
else //do something else

您可能应该打印出无效命令的内容--至少在尝试调试该命令时是这样的。。。。
String str1;
String str2;

if (str1.equals(str2)) // do something
else //do something else