通过实例可以更好的了解java

21-例子1
import java.applet.*;import java.awt.*;
import java.awt.event.*;import java.net.*;
public class Example21_1 extends Applet implements ItemListener
{ Choice choice1;TextField text1,text2;
  URL url1,url2,url3,url4,url5,url6;
  String s1,s2,s3,s4,s5,s6; 
  public void init()
  { setLayout(new GridLayout(2,2));
    choice1=new Choice();
    text1=new TextField(10); text2=new TextField(10);
    choice1.add("清华大学");choice1.add("大连理工");
    choice1.add("yahoo"); choice1.add("263");
    add(choice1);add(new Label("选择一个网址") );add(text1); add(text2);
    choice1.addItemListener(this);
    s1="http://www.tsinghua.edu.cn";
    s2="http://www.dlut.edu.cn";
    s3="http://www.yahoo.com";
    s4="http://freemail.263.net";
  }   
  public void itemStateChanged(ItemEvent e)
  {  
    if(e.getItemSelectable()==choice1)
      {
         if(choice1.getSelectedIndex()==0)
        { try
            {url1=new URL(s1);
            }
          catch(MalformedURLException g)
            { System.out.println("不正确的URL:"+url1);
            }
         text1.setText("清华大学") ;
         getAppletContext().showDocument(url1);
        }
       else if(choice1.getSelectedIndex()==1)
        { try
            {url2=new URL(s2);
            }
          catch(MalformedURLException g)
            { System.out.println("不正确的URL:"+url2);
            }
          text1.setText("大连理工") ;
          getAppletContext().showDocument(url2);
        } 
        else if(choice1.getSelectedIndex()==2)
        { try
            {url3=new URL(s3);
            }
          catch(MalformedURLException g)
            { System.out.println("不正确的URL:"+url3);
            }
          text1.setText("yahoo") ;
          getAppletContext().showDocument(url3);
        } 
       else if(choice1.getSelectedIndex()==3)
        { try
            {url4=new URL(s4);
            }
          catch(MalformedURLException g)
            { System.out.println("不正确的URL:"+url4);
            }
          text1.setText("263") ;
          getAppletContext().showDocument(url4);
        } 
      }
    else {}
 }
}


21-例子2
import java.applet.*;import java.awt.*;
import java.awt.event.*;import java.net.*;
public class Example21_2 extends Applet implements ActionListener
{ Choice choice; Button button;
  URL url; TextField text; String s1,s2,s3,s4; 
  public void init()
  { setLayout(new GridLayout(2,2));
    text=new TextField(10); button=new Button("确定");
    choice=new Choice();
    s1="http://www.tsinghua.edu.cn";
    s2="http://www.dlut.edu.cn";
    s3="http://www.yahoo.com"; s4="http://cctv.com";
    choice.add(s1); choice.add(s2);
    choice.add(s3); choice.add(s4);
    add(choice);add(button ); add(text); add(new Label());
    button.addActionListener(this);
  }   
  public void actionPerformed(ActionEvent e)
  {  
    if(e.getSource()==button)
    { try
           {url=new URL(choice.getSelectedItem());
            text.setText("请等待....."); 
           }
       catch(MalformedURLException g)
           { System.out.println("不正确的URL:"+url);
           }
         getAppletContext().showDocument(url);
    }
    else 
    { }
  }
}



21-例子3
import java.applet.*;import java.awt.*;
import java.awt.event.*;import java.net.*;
public class Example21_3 extends Applet implements ActionListener
{ Button button;
  URL url;
  TextField text;
  public void init()
  { text=new TextField(18);
    button=new Button("确定");
    add(new Label("输入网址:"));add(text); add(button);
    button.addActionListener(this);
  }   
  public void actionPerformed(ActionEvent e)
  {  
  if(e.getSource()==button)
  { try
    {url=new URL(text.getText().trim());//trim()的作用是去掉字符串的前后空格
    }
    catch(MalformedURLException g)
         { text.setText("不正确的URL:"+url);
         }
       getAppletContext().showDocument(url);
  }
 }
}



21-例子4 
(1)客户端程序：
import java.io.*;
import java.net.*;
public class Client
{ public static void main(String args[])
  { String s=null;Socket mysocket;
    DataInputStream in=null;
    DataOutputStream out=null;
    try{
     mysocket=new Socket("localhost",4331);
     in=new DataInputStream(mysocket.getInputStream());
     out=new DataOutputStream(mysocket.getOutputStream()); 
     out.writeUTF("你好！");//通过 out向"线路"写入信息。
      while(true)
      { s=in.readUTF();//通过使用in读取服务器放入"线路"里的信息
         if (s!=null)  break;
      } 
     mysocket.close();
    }
    catch(IOException e){System.out.println("无法连接");}     
    System.out.println(s); 
   } 
}
(2)服务器端程序：
import java.io.*;import java.net.*;
public class Server
{ public static void main(String args[])
  {  ServerSocket server=null;
     Socket you=null;String s=null;
     DataOutputStream out=null;DataInputStream  in=null;
     try{ server=new ServerSocket(4331);}
      catch(IOException e1){System.out.println("ERRO:"+e1);} 
     try{  you=server.accept();
           in=new DataInputStream(you.getInputStream());
           out=new DataOutputStream(you.getOutputStream());
         while(true)
         {s=in.readUTF();// 通过使用in读取客户放入"线路"里的信息
            if (s!=null) break; 
         }
        out.writeUTF("你好:我是服务器");//通过 out向"线路"写入信息
        you.close(); 
        } 
      catch (IOException e)
      {System.out.println("ERRO:"+e);}
   }
}



21-例子5
(1)客户端程序
import java.net.*;
import java.io.*;
import java.awt.*;import java.awt.event.*;
import java.applet.*;
public class ChatRoom extends Applet implements Runnable,ActionListener
{ Button button;TextField text1;TextArea text2;
  Socket socket;
  DataInputStream in;
  DataOutputStream out;
  Thread thread; 
 public void init()
 {setBackground(new Color(113,163,139));
  setLayout(new BorderLayout());
  button=new Button("send");text1=new TextField(12);
  text2=new TextArea();
  Panel p=new Panel();p.add(text1);p.add(button);
  add("Center",text2);add("South",p);
  button.addActionListener(this);
 }
 public void start()
 { try
   {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.setPriority(Thread.MIN_PRIORITY);
  thread.start();
  }
 }
 public void run()
  {String s1=null;
    while(true)
     { try{s1=in.readUTF();// 通过使用in读取服务器放入"线路"里的信息
          }
       catch (IOException e) {}
       if(s1.equals("bye"))
        {try{socket.close();break;}
         catch (IOException e) {}   
        }
       text2.append(s1+"\n");
     }
   }
  public void actionPerformed(ActionEvent e)
  {if (e.getSource()==button)
     { String s=text1.getText();
       if(s!=null)		      
        { try{out.writeUTF(s);}
          catch(IOException e1){} 
        }               
       else
        { try{out.writeUTF("请说话");}
          catch(IOException e1){} 
        }
      }
  }
}
(2)服务器端程序
import java.io.*;import java.net.*;
import java.util.*;
public class ServerTwo 
{  
  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"+"ERRO:"+e1);} 
      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;}//继续等待客户的呼叫
    }
  }
}
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)
    { try{s=in.readUTF();// 通过使用in读取客户放入"线路"里的信息
            }
       catch (IOException e) {System.out.println("ERRO:"+e);}
       try {if(s.equals("bye"))
             {out.writeUTF(s);socket.close() ; }//客户以离开
else{ try{out.writeUTF("我是服务器你对我说："+s);}
                                      //通过 out向"线路"写入信息
                   catch (IOException e) {}
                  }
           }
       catch (IOException e) {}
     }
  } 
}




21-例子6
(1) 客户端程序
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
   {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.setPriority(Thread.MIN_PRIORITY);
    thread.start();
   }
 }