1) 客户端

import java.net.*;

import java.io.*;

import java.awt.*;

import java.awt.event.*;

import java.applet.*;

public class Computer_client extends Applet implements Runnable,ActionListener

{ 

   Button 计算;TextField 输入三边长度文本框,计算结果文本框;

   Socket socket=null;

   DataInputStream in=null; DataOutputStream out=null;

   Thread thread;

   public void init()

   { 

      setLayout(new GridLayout(2,2));

      Panel p1=new Panel(),p2=new Panel();

      计算=new Button(" 计算");

      输入三边长度文本框=new TextField(12);

      计算结果文本框=new TextField(12);

      p1.add(new Label("输入三角形三边的长度,用逗号或空格分隔:"));

    p1.add( 输入三边长度文本框);

      p2.add(new Label("计算结果："));

      p2.add(计算结果文本框);

      p2.add(计算);

      计算.addActionListener(this);

      add(p1);

     add(p2);

   }

   public void start()

   {

       try

         {  //和小程序所驻留的服务器建立套接字连接：

            socket = new Socket(this.getCodeBase().getHost(), 4331);

            in =new DataInputStream(socket.getInputStream());

            out = new DataOutputStream(socket.getOutputStream());

         }

      catch (IOException e){}

      if(thread == null)

        { 

           thread = new Thread(this);

           thread.start();

        }

   }

   public void run()

   { 

      String s=null;

      while(true)

       {  

             try{ 

                  s=in.readUTF();//堵塞状态，除非读取到信息。

                  计算结果文本框.setText(s);

               }

           catch(IOException e)

{ 

   计算结果文本框.setText("与服务器已断开");

   break;

}  

       }

  }

  public void actionPerformed(ActionEvent e)

  {

     if(e.getSource()==计算)

      { 

         String s=输入三边长度文本框.getText();

         if(s!=null)

           {

               try { 

                     out.writeUTF(s);

                  }

              catch(IOException e1){}

           }              

     }

  }

}

 (2) 服务器端．

import java.io.*;

import java.net.*;

import java.util.*;

public class Computer_server

{

   public static void main(String args[])

   { 

      ServerSocket server=null;

      Server_thread thread;

      Socket you=null;

      while(true)

       {

           try{ 

                server=new ServerSocket(4331);

             }

          catch(IOException e1)

             { 

                System.out.println("正在监听"); //ServerSocket对象不能重复创建。

             }

          try{ 

                you=server.accept();

                System.out.println("客户的地址:"+you.getInetAddress());

             }

         catch (IOException e)

             { 

                System.out.println("正在等待客户");

             }

         if(you!=null)

             { 

                new Server_thread(you).start(); //为每个客户启动一个专门的线程。 

             }

         else

             { 

                continue;

             }

      }

   }

}

class Server_thread extends Thread

{ 

   Socket socket;

   DataOutputStream out=null;

   DataInputStream  in=null;

   String s=null;

   Server_thread(Socket t)

   { 

      socket=t;

      try  {

             in=new DataInputStream(socket.getInputStream());

             out=new DataOutputStream(socket.getOutputStream());

          }

      catch (IOException e)

          {}

   } 

   public void run()       

   { 

      while(true)

      { 

         double a[]=new double[3] ;int i=0;

         try{  s=in.readUTF();堵塞状态，除非读取到信息。

  StringTokenizer fenxi=new StringTokenizer(s," ,");

                 while(fenxi.hasMoreTokens())

                   { 

                      String temp=fenxi.nextToken();

                      try{ 

                           a[i]=Double.valueOf(temp).doubleValue();i++;

                         }

                      catch(NumberFormatException e)

  { 

      out.writeUTF("请输入数字字符");

                         }

                   }

                double p=(a[0]+a[1]+a[2])/2.0;

                out.writeUTF(" "+Math.sqrt(p*(p-a[0])*(p-a[1])*(p-a[2])));

                sleep(2);   

            }

         catch(InterruptedException e){}

         catch (IOException e)

            { 

               System.out.println("客户离开");

  break;

            }

      }

   }

}