最近我在做多線程聊天應用程序?，F在我正在與服務器斗爭。我試圖通過引入新字段來停止服務器online，但這沒有幫助。import view.ChatHub;import java.io.IOException;import java.io.PrintWriter;import java.lang.reflect.Array;import java.net.ServerSocket;import java.net.Socket;import java.util.ArrayList;import java.util.Set;import java.util.HashSet;import java.util.Scanner;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;public class ChatServer extends Thread {    // All client names, so we can check for duplicates upon registration.    private static Set<String> names = new HashSet<>();    // The set of all the print writers for all the clients, used for broadcast.    private static Set<PrintWriter> writers = new HashSet<>();    private ChatHub frame;    private int port;    private boolean online;    private ExecutorService pool;    public ChatServer(int port) throws IOException {        System.out.println("The chat server is running...");        this.frame = new ChatHub(this);        this.port = port;        this.online = true;        this.pool = Executors.newFixedThreadPool(500);        this.start();    }    @Override    public void run() {        while (this.online) {            try (ServerSocket listener = new ServerSocket(this.port)) {                this.pool.execute(new Handler(listener.accept(), this.names, this.writers));            } catch (IOException e) {                e.printStackTrace();            }        }    }    public void stopChatServer() {        this.pool.shutdown();        this.online = false;    }    public Set<String> getNames() {        return this.names;    }    public Set<PrintWriter> getWriters() {        return this.getWriters();    }    public ChatHub getFrame() {        return this.frame;    }    public int getPort() {        return this.port;    }}