java - 无法在线程的构造函数中初始化 PrintWriter 字段

Question

需要为每个连接创建一个新线程。线程应该具有写入套接字的功能，即使它正在 run() 中等待客户端输入:String clientCommand = in.readLine()。函数update应该满足这个要求，并且能够使用PrintWriter outWr写入套接字，但它似乎是null，即使将其设置为线程构造函数。无法在构造函数中初始化 PrintWriter outWr。在 try 构造之后，outWr 仍然为 null。如何解决？

<小时/>

public class Server {
    public static void main(String[] args) { 
        ...
        ClientServiceThread cliThread = new ClientServiceThread(clientSocket, id++, auction);
        ...
}

<小时/>

public class ClientServiceThread extends Thread  {
private PrintWriter outWr;

ClientServiceThread(Socket s, int clientID, Auction a) {
        try {
            PrintWriter outWr = new PrintWriter(new OutputStreamWriter(
                    m_clientSocket.getOutputStream()));
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
public void run() {....; String clientCommand = in.readLine(); ... }
public void update(String msg){outWr.println(msg);}

Answer 1

看看这段代码

public class ClientServiceThread extends Thread  {
private PrintWriter outWr;

ClientServiceThread(Socket s, int clientID, Auction a) {
        try {
            PrintWriter outWr = new PrintWriter(new OutputStreamWriter(

在构造函数中，您不初始化类字段，而是初始化本地引用PrintWriter outWr

更改为

        try {
            outWr = new PrintWriter(new OutputStreamWriter(