服务器端请求的Java线程ArrayList

Question

我正在开发一个简单的邮件服务器，以学习如何在Java中使用套接字。 为了处理多个请求，我使用以下解决方案：

         while(true){
            if(currentThread == -1){
                currentThread++;
                connectionThreads.add(new ConnectionThread(serverSocket));
                connectionThreads.get(currentThread).setDaemon(true);
                connectionThreads.get(currentThread).start();
                System.out.println("STARTED thr " + currentThread);
            }
            if(connectionThreads.get(currentThread).isConnected()){
                System.out.println("THREAD CONNECTED: Thr " + currentThread);
                currentThread++;
                connectionThreads.add(new ConnectionThread(serverSocket));
                connectionThreads.get(currentThread).setDaemon(true);
                connectionThreads.get(currentThread).start();
                System.out.println("STARTED thr " + currentThread);
            }
        }

其中“ currentThread”是整数，connectionThreads是客户端套接字的ArrayList，serverSocket是所有客户端套接字绑定到的服务器套接字。 问题是，当我将客户端连接到服务器时，它在第一个/第二个线程中运行良好，然后卡住了： 视频输出为：

STARTED thr 0
THREAD CONNECTED: Thr 0
STARTED thr 1

但是，如果我添加以下else语句：

         while(true){
            if(currentThread == -1){
                currentThread++;
                connectionThreads.add(new ConnectionThread(serverSocket));
                connectionThreads.get(currentThread).setDaemon(true);
                connectionThreads.get(currentThread).start();
                System.out.println("STARTED thr " + currentThread);
            }
            if(connectionThreads.get(currentThread).isConnected()){
                System.out.println("THREAD CONNECTED: Thr " + currentThread);
                currentThread++;
                connectionThreads.add(new ConnectionThread(serverSocket));
                connectionThreads.get(currentThread).setDaemon(true);
                connectionThreads.get(currentThread).start();
                System.out.println("STARTED thr " + currentThread);
            }else System.out.println(currentThread + " isConnected " + connectionThreads.get(currentThread).isConnected());
        }

它工作正常。

谁能告诉我发生了什么事？

谢谢！ ：-）