其实这个问题以前已经有请教过了，后来几经折腾，有了一点改进，但问题还是没有彻底解决。特再来请教。
我的要求是点击按钮即可实现服务器端口的打开或关闭。目前程序每第一次按下打开按钮，端口可以打开，再按下关闭按钮，端口也可以关闭，但仅限于第一次操作。此后打开关闭按钮便不再起作用，我想可能是线程未结束的原因造成的，可就算我使用不被推荐的stop方法，依然如此。请专家指明根源，谢谢了。
源码在此：

import java.io.*;
import java.net.*;
import java.util.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class Clk_Server
{    public static void main(String[] args)
    {    
        JFrame frame=new ServerFrame();
        frame.show();
    }
}

class ServerFrame extends JFrame implements ActionListener
{    public ServerFrame()
    {    JPanel p=new JPanel();
        startButton =new JButton("打开");
        p.add(startButton);
        startButton.addActionListener(this);
        getContentPane().add(p,"South");
        textArea=new JTextArea(8,40);
        scrollPane=new JScrollPane(textArea);
        getContentPane().add(scrollPane,"Center");
        
        setTitle("服务器");
        setSize(500,300);
        
        ServerOpen=new ServerHandler();
        
        addWindowListener(new WindowAdapter()
            {    public void windowClosing(WindowEvent e)
                {    System.exit(0);
                }
            });
    }
    public void actionPerformed(ActionEvent evt)
    {    
        Object source=evt.getSource();
        if (source==startButton)
        {    
            if (startButton.getText()!="打开")
            {
                startButton.setText("打开");
                ServerOpen.shutoff();
            }
            else
            {    
                startButton.setText("关闭");
                ServerOpen.start();
            }
        }
    }

    private JButton startButton;
    private JScrollPane scrollPane;
    private JTextArea textArea;
    private ClkServer server;
    private ServerHandler ServerOpen;
    private Thread newHandlerThread;
}

class ServerHandler extends Thread 
//implements Runnable 
{
    private static final int SERVER_PORT=8189;
    private static final int MAX_CLIENTS=100;
    private boolean keepRunning=false;
    private ServerSocket listenSocket=null;
    
      public void run() 
    {    Socket clientSocket = null;
        try
        {    
            listenSocket=new ServerSocket(SERVER_PORT,MAX_CLIENTS);
            while (true)
            {    try
                {    
                    sleep(5);
                }
                catch(InterruptedException e)
                {    System.err.println("Sleep InterruptedException : "+e);
                }
                // Accept a new client.
                  clientSocket = listenSocket.accept();
                //System.out.println("link link link ...");
               
                // Create a new handler.
                //StockQuoteHandler newHandler = new StockQuoteHandler(clientSocket,stockInfo,stockInfoTime);
                //Thread newHandlerThread = new Thread(newHandler);
                //newHandlerThread.start();
            }
        }
        catch(IOException excpt)
        {    System.err.println("Unable to listen on port "+SERVER_PORT+" : "+excpt);
            shutoff();
            return;
        }
      }
        
    protected void status(boolean Status) 
    {
        keepRunning = Status;
    }
    public void shutoff() 
    {    try
        {    //System.out.println("Socket Closed _shutoff.");
            listenSocket.close();
        }
        catch(IOException excpt) 
        {
            System.err.println("Failed I/O: "+ excpt);
          }
    }
} 

你程序的问题是，线程是不可以重入的。所以你在线程退出后在start是不行的。
所以这样就行了。
class ServerFrame extends JFrame implements ActionListener
{    public ServerFrame()
    {    JPanel p=new JPanel();
        startButton =new JButton("´ò¿ª");
        p.add(startButton);
        startButton.addActionListener(this);
        getContentPane().add(p,"South");
        textArea=new JTextArea(8,40);
        scrollPane=new JScrollPane(textArea);
        getContentPane().add(scrollPane,"Center");
        
        setTitle("·þÎñÆ÷");
        setSize(500,300);
        
        
        
        addWindowListener(new WindowAdapter()
            {    public void windowClosing(WindowEvent e)
                {    System.exit(0);
                }
            });
    }
    public void actionPerformed(ActionEvent evt)
    {    
        Object source=evt.getSource();
        if (source==startButton)
        {    
            if (startButton.getText()!="´ò¿ª")
            {
                startButton.setText("´ò¿ª");
                ServerOpen.shutoff();
            }
            else
            {    
                startButton.setText("¹Ø±Õ");
                ServerOpen=new ServerHandler();
                ServerOpen.start();
            }
        }
    }

    private JButton startButton;
    private JScrollPane scrollPane;
    private JTextArea textArea;
    private ServerHandler ServerOpen;
    private Thread newHandlerThread;
}