Java TCP if 语句

Question

对于此应用程序，命令来自用户，服务器发回回复。 if 语句由于某种原因不起作用，对于每个输入，它都会运行 sentence = "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);
        }
    }
        }

Answer 1

您应该使用 .equals() 方法来比较字符串，而不是使用 ==。

更改

  if(capitalizedSentence == "VERSION"){

为

  if(capitalizedSentence.equals("VERSION")){

Answer 2

要比较字符串，您必须使用 .equals() 方法，如下所示：

String str1;
String str2;

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