实际上是这样 NullPointerException 因为 socketConnect 从未初始化，您必须初始化它，您可以在 main 方法，当然您必须将它们声明为 static .

// static variable
public static ServerSocket socketServer = null;
public static Socket socketConnect = null;

public static void main(String[] args) throws IOException {
    ChatServer cc = new ChatServer();
    cc.socketServer = new ServerSocket(2000);
    java.awt.EventQueue.invokeLater(new Runnable() {
        public void run() {
            new ChatServer().setVisible(true);
        }
    });
    cc.socketConnect = cc.socketServer.accept();
    System.out.println(cc.socketConnect.isConnected());

    // instance
    socketServer = cc.socketServer;
    socketConnect = cc.socketConnect;
}

// now you can use socketConnect, cause you did init in main at the final from the main method
public void send(String msg) throws IOException {
    System.out.println(this.socketConnect.isConnected());
}

德国劳埃德船级社
对不起，我的英语不好。