我修改了github上的一个开源项目作为一个学校项目，以满足我的需要，它有一个 broadcast() 方法发送消息，并在 run() 方法，但问题是 broadcast() 将消息发送给 userList<> 我想添加一个功能，通过编写 @username .
以下是广播方法的代码：

private synchronized void broadcast(String msg) {
    for (int i = 0; i < clientList.size(); i++) {
        clientList.get(i).write(msg);
    }
    System.out.println("Log: Message broadcast --> " + msg);
}

下面是run（）方法

public void run() {
    System.out.println("Log: Got input/output streams for connected client.");

    /**Get the first message from the client, attempt communication */
    String clientMsg = null;
    boolean accepted = false;

    /**Allow client to create an account, login, or quit */
    do {
        clientMsg = client.read();
        if (clientMsg.equals("QUIT")) {
            System.out.println("Log: Client disconnected without signing in.");
            client.disconnect();
            return;
        }
        else if (clientMsg.startsWith("NEWUSER: ")) {
            createUser(clientMsg);
        }
        else if (clientMsg.startsWith("LOGIN: ")) {
            accepted = authenticate(clientMsg);
        }
        else
        {
            System.out.println("Log: Unexpected client message -> " + clientMsg);
            client.disconnect();
            return;
        }
    } while(!accepted);

    /**Run main chat loop. Will read from the client, and broadcast each read
     *  until the client disconnects. */
    while (true) {
                int i=0;
                String username= clientList.get(i).getUsername();
        String line = client.read();
        if (line == null) break;
                    else if(line.startsWith("@"+username)){
                     broadcastp(line,username);
                    }
        else {

                        broadcast(line);

                    }
i++;
    }

    /**The only way for the client to exit the above loop is to disconnect.
     *  Therefore, call the handler's exit routine */
    exit();
}

这是你的名字 broadcastp() 方法，但它不起作用。它的编译和运行非常完美，尽管没有私人聊天功能。

private synchronized void broadcastp(String msg,String username) {
             for (int i = 0; i < clientList.size(); i++) {
        username = clientList.get(i).getUsername();
        if(msg.startsWith("@"+username))
        {clientList.get(i).write(msg);}
        else {
        continue;
        }}
    System.out.println("Log: Message broadcast --> " + msg);}