通过实例可以更好的了解java

 public void run()
 {String s=null;
    while(true)
     { try{s=in.readUTF();
          }
         catch (IOException e) 
{计算结果文本框.setText("与服务器已断开");break;}   
       计算结果文本框.setText(s);
     }
 }
 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) 服务器端程序:
import java.io.*;import java.net.*;
import java.util.*;import java.sql.*;
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");} 
      try{ you=server.accept();}
      catch (IOException e)
      {System.out.println("正在等待客户");}
      if(you!=null) 
      {new Server_thread(you).start();   }
      else {continue;}
    }
  }
}
class Server_thread extends Thread
{  Socket socket;Connection Con=null;Statement Stmt=null;
   DataOutputStream out=null;DataInputStream  in=null;int n=0;
   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(); 
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");
Thread.currentThread().yield();break;
          }
     }
   } 
}



21-例子7
(1)客户端的 Java Applet:
import java.net.*;
import java.io.*;
import java.awt.*;import java.awt.event.*;
import java.applet.*;
class Mywindow extends Frame implements ActionListener
{   TextField text1,text2;Button button1,button2;
   Mywindow()
    {super("发悄悄话窗口");
     setLayout(new GridLayout(3,2));
     text1=new TextField(12);text2=new TextField(8);
     button1= new Button("送出悄悄话");button2=new Button("关闭此窗口");
     add(new Label("送悄悄话到:"));add(text1);add(new Label("输入您的悄悄话:"));
     add(text2);add(button2);add(button1);
     setSize(400,190);text1.setEditable(false);setVisible(false);
     button1.addActionListener(this); button2.addActionListener(this);
     setBackground(Color.pink);
   }
   public void actionPerformed(ActionEvent e)
   {if(e.getSource()==button1)
{ try{ chatappletthree.out.writeUTF("悄悄地对"+text1.getText()+
"说:"+text2.getText()+"(我是"+chatappletthree.baocun+")");}
      catch(IOException e1) {}
    }
    else if(e.getSource()==button2)
    { this.setVisible(false);}
   }
} 

class Apanel extends Panel
{ TextField name_txt; Button button1,button2;
Checkbox box1,box2,box3;CheckboxGroup sex;
  Apanel()
  { name_txt=new TextField(10); button1=new Button("进入聊天室");
     button2=new Button("退出聊天室");
    setLayout(new FlowLayout());sex=new CheckboxGroup();
     box1=new Checkbox("男M",false,sex);
    box2=new Checkbox("女F",false,sex);
    box3=new Checkbox("蘑菇",false,sex);
     add(new Label("输入昵称")) ;add(name_txt);add(box1);
     add(box2);add(box3);add(button1);add(button2);
     add(new Label("制作:张跃平,耿祥义([e-mail])"));
  }  
}
class Bpanel extends Panel
{ TextArea chat_txt;  B2panel b2;
  Bpanel()
  { chat_txt=new TextArea(20,75); 
    b2=new B2panel();
    chat_txt.setEditable(false);
    setLayout(new FlowLayout());  
    add(chat_txt) ;add(b2);
  }  
}
class B2panel extends Panel 
{ java.awt.List list;
  B2panel()
 { try{ list =new java.awt.List(25,false);}
   catch(NullPointerException e){}
   setLayout(new BorderLayout());
   add("Center",list); add("North",new Label("聊天者列表："));
   add("East", new Label());
   add("South",new Label("双击某昵称可悄悄话"));
 } 
}  
class Cpanel extends Panel
{ TextField msg_txt; Button button,button2,button3;
  Cpanel()
  { msg_txt=new TextField(66); button=new Button("送出信息");
    button2=new Button("刷新谈话区");
   button3=new Button("刷新聊天者列表区");
    setLayout(new FlowLayout());
    add(new Label("您要说的话:"));add(msg_txt) ;
    add(button);add(button2);add(button3);
  }  
}
public class chatappletthree extends Applet implements Runnable,
ActionListener,ItemListener
{public static final int PORT = 8765; static String baocun,xingbie;
 Socket socket;int jilu,enter=1;
 DataInputStream in;
 static DataOutputStream out;
 Thread thread; String line;
 static Apanel a;static Bpanel b;static  Cpanel c;
 static Mywindow mywindow;
 public void init()
 {mywindow=new Mywindow();
  setBackground(new Color(113,163,139));
  setLayout(new BorderLayout());
  a=new Apanel();  b=new Bpanel();  c=new Cpanel();
  add("North",a);add("Center",b);add("South",c);
  a.button1.addActionListener(this);
  a.button2.addActionListener(this);
  c.button.addActionListener(this);
  c.button2.addActionListener(this);
  c.button3.addActionListener(this);
  a.box1.addItemListener(this); 
  a.box2.addItemListener(this); 
   a.box3.addItemListener(this);
  b.b2.list.addActionListener(this);
  add("East",new Label());
  add("West",new Label());
  jilu=0; this.setForeground(Color.black);
  c.msg_txt.setBackground(Color.yellow);
  b.chat_txt.setBackground(new Color(200,185,220));
  b.chat_txt.setFont( new Font("TimeRoman", Font.PLAIN, 16));
}
public void start()
{try{socket = new Socket(this.getCodeBase().getHost(), PORT);
 in = new DataInputStream(socket.getInputStream());
 out = new DataOutputStream(socket.getOutputStream());	}
 catch (IOException e){this.showStatus(e.toString());
 say("欢迎来这里!");System.exit(1);
 }say("欢迎来红蜘蛛聊天室");
 if (thread == null){
 thread = new Thread(this);
 thread.setPriority(Thread.MIN_PRIORITY);
 thread.start();
 }
}
public void stop()
{try{
  socket.close();
  } catch (IOException e){
  this.showStatus(e.toString());
 }
 if ((thread !=null) && thread.isAlive())
{thread.yield();thread = null;
}
}
 public void destroy()
{ try{out.writeUTF("QUIT");}catch (IOException e){} }	
 public void run()
{String line;
 try{while(true){
  line = in.readUTF();
  if(line.startsWith("PEOPLE"))
  {b.b2.list.add(line.substring(6));
  b.chat_txt.append(line.substring(6)+"爬上红蜘蛛网→"+'\n' );
  }
  else if(line.startsWith("MSG"))
  {b.chat_txt.append(line.substring(3)+'\n' );}
   else if(line.startsWith("QUIT"))
  {String str=line.substring(10);
  try{ for(int i=0,k=0;i<=120;i++)
  { String s=b.b2.list.getItem(i);
   if(s.equals(str))
  { k=i;b.b2.list.remove(k);}
    b.chat_txt.append(line.substring(10)+"←高兴地离开了红蜘蛛网"+'\n');
  }
 }
catch(ArrayIndexOutOfBoundsException e){}       
 }
else if(line.startsWith("悄悄地对"))
{ String ti=null;
  ti= line.substring(line.indexOf(':'));
  if(ti.startsWith(":zhangpgxygsrok")&&(!(ti.endsWith("*"))))
 {this.out.writeUTF("BADQUIT");
 b.chat_txt.append("@@@@请注意!!!:"+baocun+"["+xingbie+"]"+","+
"你被踢出红蜘蛛网,注意言行哦!@@@@"+'\n');
 }
 else
 {b.chat_txt.append(line+'\n');}              
 }
 }
} 
catch (IOException e) { say("再见！欢迎再来红蜘蛛聊天室，如果想重新进入本聊天室，单击浏览器的刷新选项");  }
catch(NullPointerException e) {}
}
public void actionPerformed(ActionEvent e)
{if (e.getSource()==c.button)
 { if((baocun!=null))
  { String ti=c.msg_txt.getText();
  if(ti.equals("zhangpgxygsrok"))		      
 { try{out.writeUTF("坏悄悄地对:"+c.msg_txt.getText());}catch(IOException e1){}  }  
  else
 {try{out.writeUTF("MSG"+baocun+"["+xingbie+"]"+
"说(Speaking)→ "+":"+c.msg_txt.getText());
  c.msg_txt.setText(null);}
 catch(IOException e1){}
 }	
}
}   
 else if(e.getSource()==c.button2)
 { b.chat_txt.setText(null);
 }
 else if(e.getSource()==c.button3)
 { try{b.b2.list.removeAll();	out.writeUTF("newlist");} 
   catch(IOException e1){}
 }
else if(e.getSource()==a.button1)
{ {baocun=new String(a.name_txt.getText());}
 try{ for(int i=0;i<=120;i++)
{if((a.name_txt.getText()!=null)&&
   ((a.name_txt.getText()+"["+xingbie+"]").equals(b.b2.list.getItem(i))||
    a.name_txt.getText().equals("该名已被使用")))
  {jilu=1; baocun=null;  break;}
} 
} 
catch(ArrayIndexOutOfBoundsException e3){}
if(jilu==0)
{try{out.writeUTF("PEOPLE"+a.name_txt.getText()+"["+xingbie+"]");
}
catch(IOException e1){}
}
 else if(jilu==1)
{ a.name_txt.setText("该名已被使用");}
jilu=0;            
}
else if(e.getSource()==a.button2)
 { try{out.writeUTF("QUIT");}
    catch(IOException e1){}
 b.b2.list.removeAll(); 
}
else if(e.getSource()==b.b2.list)
{  mywindow.setVisible(true);
   mywindow.text1.setText(((List)e.getSource()).getSelectedItem());
}
}
public void itemStateChanged(ItemEvent e1)
   {  if(e1.getItemSelectable()==a.box1)
         {xingbie="男";}
       else if(e1.getItemSelectable()==a.box2)
          {xingbie=new String("女");}
       else if(e1.getItemSelectable()==a.box3)
          {xingbie=new String("蘑菇");}
      else if((a.box1.getState()==true)&&
             ((a.box1.getState()==true)&&
             (a.box1.getState()==true)))
             { xingbie="单细胞";}
      } 
    public void say(String msg)
 {b.chat_txt.append("☆☆☆☆☆ "+msg+" ☆☆☆☆☆\n");
 }
}

(2)服务器端程序
import java.net.*;import java.io.*;
import java.util.*;import java.net.*;
import java.io.*;
public class chatserverthree implements Runnable
{public static final int PORT = 8765;
 protected ServerSocket listen;
 static Vector connections;Thread connect;
public chatserverthree()
{try
{listen = new ServerSocket(PORT);
} catch (IOException e)
{System.err.println("erro:"+e); System.exit(1);
 }
connections =new Vector(1000);connect = new Thread(this);
connect.start();
}
public void run()
{try{while(true)