客户端和服务器端的 Java 套接字问题

Question

我在比较从客户端发送到服务器的字符串时遇到问题。我试图从客户端读取消息“HELLO”，然后从服务器返回“hello”。我的问题是，当我到达服务器类中的 if 语句时，我总是点击 else 。我相信我无法理解哪些行正在收集数据或只是打印。同时要做一些研究，我想学好这个。知道为什么吗，提前谢谢您？

服务器类别:

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

public class Server {

    public static void main(String[] args) throws Exception
    {
        Server myServer = new Server();
        myServer.run();
    }

    public void run() throws Exception
    {

        //Initializes the port the serverSocket will be on
        ServerSocket serverSocket = new ServerSocket(4200);
            System.out.println("The Server is waiting for a client on port 4200");
        //Accepts the connection for the client socket
        Socket socket = serverSocket.accept();

        InputStreamReader ir = new InputStreamReader(socket.getInputStream());
        BufferedReader br = new BufferedReader(ir);
        String message = br.readLine();
        //Confirms that the message was received
        System.out.println(message);

            if(message == "HELLO")
            {
                PrintStream ps = new PrintStream(socket.getOutputStream());
                ps.println("Received our hello message.");
            }
            else
            {
                PrintStream ps = new PrintStream(socket.getOutputStream());
                ps.println("Did not receive your hello message");
            }
    }

}

客户端类:

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

public class Client {

    public static void main(String[] args) throws Exception
    {
        Client myClient = new Client();
        myClient.run();
    }

    public void run() throws Exception
    {
        Socket clientSocket = new Socket("cmps329.csit.selu.edu", 4200);
        //Sends message to the server
        PrintStream ps = new PrintStream(clientSocket.getOutputStream());
        ps.println("HELLO");
        //Reads and displays response from server
        InputStreamReader ir = new InputStreamReader(clientSocket.getInputStream());
        BufferedReader br = new BufferedReader(ir);
        String message = br.readLine();
        System.out.println(message);        
    }

}

Answer 1

使用

if (message.equals("HELLO"))

参见How do I compare strings in Java?为什么。