通过实例可以更好的了解java

20-例子1
import java.io.*;
class Example20_1
{ public static void main(String args[])
  { int b;
  byte buffer[]=new byte[2500];
  try{ FileInputStream readfile=new FileInputStream("Example211.java");
       b=readfile.read(buffer,0,2500);
       try { String str=new String(buffer,0,b,"Default");
             System.out.println(str);
           }        
       catch(UnsupportedEncodingException e)
           { System.out.println(" the encoding was not found:"+e);
           }
     }
   catch(IOException e)
     {System.out.println("File read Error ");
     }
  }
}



20-例子2
import java.io.*;import java.awt.*;import java.awt.event.*;
class Example20_2
{  static Frame f;
   public static void main(String args[])
  { int b,j=10; TextArea text;
    byte tom[]=new byte[2500];f=new Frame();
    f.setSize(100,100);text=new TextArea(30,60);
    f.setVisible(true);f.add(text); f.pack();
    f.addWindowListener(new WindowAdapter()
      { public void windowClosing(WindowEvent e)
        {f.setVisible(false);System.exit(0);}
      }); 
   
try{ File f=new File("E:\\dd\\","AA.java");
     FileInputStream readfile=new FileInputStream(f);
         while((b=readfile.read(tom,0,j))!=-1) 
          {String s=new String (tom,0,b);
            System.out.println(s);
            text.append(s); 
          }
         readfile.close();
       }
     catch(IOException e)
       {System.out.println("File read Error ");
       }
  }
}



20-例子3
import java.io.*;
class Example20_3
{ public static void main(String args[])
  { int b;
  byte buffer[]=new byte[100];
  try{System.out.println("输入一行文本，并存入磁盘：");
      b=System.in.read(buffer);//把从键盘敲入的字符存入buffer。
      FileOutputStream whritefile=new FileOutputStream("line.txt");
      whritefile.write(buffer,0,b);// 通过流把 buffer写入到文件line.txt。
     }
   catch(IOException e)
     {System.out.println("Error ");
     }
  }
}



20-例子4
import java.applet.*;
import  java.io.*;
import java.awt.*;
import java.awt.event.*;
 class EWindow extends Frame implements ActionListener
{ TextArea text; BufferedReader in;  Button button;
  FileReader file;
   EWindow()
   {super("流的读取");
    text=new TextArea(10,10);text.setBackground(Color.cyan);
try {File f=new File("e:/dd/","E2.html");
     file=new FileReader(f);
         in=new BufferedReader(file);
        }
    catch(FileNotFoundException e){}
    catch(IOException e){}   
    button =new Button("读取"); 
    button.addActionListener(this);
    setLayout(new BorderLayout());
    setSize(40,40);
    setVisible(true);
    add(text,"Center");add("South",button);
    addWindowListener(new WindowAdapter()
     {public void windowClosing(WindowEvent e)
     {setVisible(false);System.exit(0); }
     });
   } 
public void actionPerformed(ActionEvent e)
  { String s;
    if(e.getSource()==button)
     try{
         while((s=in.readLine())!=null)
         text.append(s+'\n');   
         }
      catch(IOException exp){} 
  }
}
public class Example20_4
{public static void main(String args[])
 {EWindow w=new EWindow();w.pack();
 }
}




20-例子5
import java.applet.*;
import  java.io.*;
import java.awt.*;
import java.awt.event.*;
 class FWindow extends Frame implements ActionListener
{ TextArea text; BufferedWriter out;  Button button;
  FileWriter tofile;
   FWindow()
   {super("流的写入");
    text=new TextArea(10,10);text.setBackground(Color.cyan);
    try {tofile=new FileWriter("hello.txt");
         out=new BufferedWriter(tofile);
        }
    catch(FileNotFoundException e){}
    catch(IOException e){}   
    button =new Button("写入"); 
    button.addActionListener(this);
    setLayout(new BorderLayout());
    setSize(60,70);
    setVisible(true);
    add(text,"Center");add("South",button);
    addWindowListener(new WindowAdapter()
     {public void windowClosing(WindowEvent e)
     {setVisible(false);System.exit(0); }
     });
   } 
  
 public void actionPerformed(ActionEvent e)
  { String s;
    if(e.getSource()==button)
     try {
        out.write(text.getText(),0,(text.getText()).length());
        out.flush();
         }
     catch(IOException exp){System.out.println(" have problem");} 
  }
}
public class Example20_5
{public static void main(String args[])
 {FWindow w=new FWindow();w.pack();//用紧凑方式显示窗口
 }
}



20-例子6
import java.util.*;import java.io.*;
import java.awt.*;import java.awt.event.*;
class EWindow extends Frame implements ItemListener,ActionListener
{ String str[]=new String[7];String s;
  FileReader file;BufferedReader in;  Button button_start;
  Checkbox box[];TextField text_word,text_fenshu;
  int fenshu=0;  CheckboxGroup age=new CheckboxGroup();
   EWindow()
   {super("英语单词学习");
    text_fenshu=new TextField(10);text_word=new TextField(70);
    button_start=new Button("重新练习");button_start.addActionListener(this);
    try {file=new FileReader("English.txt");
         in=new BufferedReader(file);
        }
    catch(FileNotFoundException e){}
    catch(IOException e){}   
    setBounds(100,100,400,320); setVisible(true);
    setLayout(new GridLayout(5,1));setBackground(Color.pink);
    Panel p1=new Panel(),p2=new Panel(),p3=new Panel() ,p4=new Panel();
    p2.setLayout(new GridLayout(2,1)); p3.setLayout(new GridLayout(5,1)); 
    p1.add(new Label("您的得分:"));p1.add(text_fenshu);
    p2.add(new Label("句子填空:"));p2.add(text_word); 
    p4.add(button_start); box=new Checkbox[6];
    for(int i=0;i<=4;i++)
     {box[i]=new Checkbox(" ",false,age);
      box[i].addItemListener(this);
     } 
    p3.add(new Label("选择答案："));
    for(int i=1;i<=4;i++)
     {p3.add(box[i]);}         
     add(p1); add(p2);add(new Label()); add(p3);add(p4);
     addWindowListener(new WindowAdapter()
     {public void windowClosing(WindowEvent e)
     {setVisible(false);System.exit(0); }
     });
     reading();
   } 
public void reading()
 {int i=0; 
  try{ s=in.readLine();
       if(!(s.startsWith("endend")))
       {StringTokenizer tokenizer=new StringTokenizer(s,"#"); 
        while(tokenizer.hasMoreTokens())
         {str[i]=tokenizer.nextToken();i++;
         }
        text_word.setText(str[0]);
        for(int j=1;j<=4;j++)
        {box[j].setLabel(str[j]);
        } 
       }
      else if(s.startsWith("endend"))
       { text_word.setText("学习完毕"); 
         for(int j=1;j<=4;j++)
          {box[j].setLabel("end"); in.close();file.close();
          } 
       }
     }
  catch(IOException exp){} 
 }
public void actionPerformed(ActionEvent event)
 {if(event.getSource()==button_start)
   {file=null;in=null;fenshu=0;text_fenshu.setText("得分： "+fenshu);
    try {file=new FileReader("English.txt");
         in=new BufferedReader(file);
        }
    catch(FileNotFoundException e){}
    catch(IOException e){}  
    reading(); 
   }
 }
public void itemStateChanged(ItemEvent e)
 { for(int j=1;j<=4;j++)
   { if(box[j].getLabel().equals(str[5])&&box[j].getState())
      {fenshu++;text_fenshu.setText("得分： "+fenshu);
      }
   }
  reading();
 }
}
public class Example20_6
{public static void main(String args[])
 {EWindow w=new EWindow();w.pack();
 }
}



20-例子7
import java.awt.*;import java.io.*;
import java.awt.event.*;
public class Example20_7
{public static void main(String args[])
 { Frame_FileDialog f=new Frame_FileDialog(); }
}
class  Frame_FileDialog extends Frame implements ActionListener
{ FileDialog filedialog_save,filedialog_load;//声明2个文件对话框
  MenuBar menubar;Menu menu;MenuItem item1,item2;TextArea text;
  BufferedReader in;  
  FileReader file_reader;
  BufferedWriter out; 
  FileWriter tofile;
  Frame_FileDialog()
 {  super("带文件对话框的窗口");     
    setSize(60,70);               
    setVisible(true);    
    menubar=new MenuBar();   
    menu=new Menu("文件"); 
    item1=new MenuItem("打开文件");
    item2=new MenuItem("保存文件"); 
    item1.addActionListener(this); 
    item2.addActionListener(this);
    menu.add(item1);
    menu.add(item2); 
    menubar.add(menu);  
    setMenuBar(menubar);        
    //下面创建1个依赖于该窗口的保存文件对话框
    filedialog_save=new FileDialog(this,"保存文件话框",FileDialog.SAVE);
    filedialog_save.setVisible(false);
    //再创建1个依赖于该窗口的打开文件对话框
    filedialog_load=new FileDialog(this,"打开文件话框",FileDialog.LOAD);
    filedialog_load.setVisible(false);
    filedialog_save.addWindowListener(new WindowAdapter()//对话框增加适配器
     {public void windowClosing(WindowEvent e)
     {filedialog_save.setVisible(false);}
     });
    filedialog_load.addWindowListener(new WindowAdapter()//对话框增加适配器
     {public void windowClosing(WindowEvent e)
     {filedialog_load.setVisible(false);}
     });
    addWindowListener(new WindowAdapter()  //窗口增加适配器
     {public void windowClosing(WindowEvent e)
     {setVisible(false);System.exit(0);}
     });
    text=new TextArea(10,10);text.setBackground(Color.cyan);
    add(text,"Center");
 }
 public void actionPerformed(ActionEvent e) //实现接口中的方法
  { if(e.getSource()==item1)
    {  filedialog_load.setVisible(true);String s;
      try {//建立到文件file的FileReader流，该文件通过File类和对话框来确定
                        File file=new File(filedialog_load.getDirectory(),filedialog_load.getFile());
           file_reader=new FileReader(file);
           in=new BufferedReader(file_reader);
           while((s=in.readLine())!=null)
           text.append(s+'\n'); 
          }
    catch(FileNotFoundException e1){}
    catch(IOException e2){}
     try {in.close();
          file_reader.close();
         }
     catch(IOException exp){} 
    }
  else if(e.getSource()==item2)
    { filedialog_save.setVisible(true);
       try {//建立到文件file的FileWtiter流，该文件通过File类和对话框来确定
                      File file=new File(filedialog_save.getDirectory(),filedialog_save.getFile());
           tofile=new FileWriter(file);
           out=new BufferedWriter(tofile);
           out.write(text.getText(),0,(text.getText()).length());
           out.flush();
          }
    catch(FileNotFoundException e1){}
    catch(IOException e2){}
     try {out.close();
          tofile.close();
         }
     catch(IOException exp){} 
    }
  } 
}


20-例子8
import java.awt.*;import java.io.*;
import java.awt.event.*;
public class Example20_8
{public static void main(String args[])
 { Frame_FileDialog f=new Frame_FileDialog(); }
}
class  Frame_FileDialog extends Frame implements ActionListener
{ FileDialog filedialog_load;//声明文件对话框
  MenuBar menubar;Menu menu;MenuItem item;
  Frame_FileDialog()
 {  super("带文件对话框的窗口"); 
  setSize(60,70);               
  setVisible(true);    
  menubar=new MenuBar();   
  menu=new Menu("文件"); 
  item=new MenuItem("运行可执行文件");
  item.addActionListener(this); 
  menu.add(item);
  menubar.add(menu);  
  setMenuBar(menubar);        
  filedialog_load=new FileDialog(this,"打开文件话框",FileDialog.LOAD);
  filedialog_load.setVisible(false);
  filedialog_load.addWindowListener(new WindowAdapter()  
   {public void windowClosing(WindowEvent e)
     {filedialog_load.setVisible(false);}
     });
    addWindowListener(new WindowAdapter()  
     {public void windowClosing(WindowEvent e)
     {setVisible(false);System.exit(0);}
     });
}
 public void actionPerformed(ActionEvent e) //实现接口中的方法
  { if(e.getSource()==item)
    {  filedialog_load.setVisible(true);
      try 
{File file=
 new File(filedialog_load.getDirectory(),filedialog_load.getFile());
         Runtime ce=Runtime.getRuntime();
         ce.exec(file.toString());//把file用字符串表示,所有对象都能使用
                                 //toString()
        }
        catch(FileNotFoundException e1){}
        catch(IOException e2){}
    }
  } 
}



20-例子9
import java.io.*;
public class Example20_9
{public static void main(String args[])
 {RandomAccessFile in_and_out=null;
 int data[]={124,389,33,256,-90,34,21,7,100,25};
 try{in_and_out=new RandomAccessFile("tom.dat","rw");}
 catch(FileNotFoundException e){System.out.println("PPPP?????");}
 try{for(int i=0;i<data.length;i++)
    {in_and_out.writeInt(data[i]);
    } 
  for(long i=data.length-1;i>=0;i--)//一个int型数据占4个字节，我们从
  {in_and_out.seek(i*4);               //文件的第36个字节读取最后面的一个整数，
  System.out.print(","+in_and_out.readInt());//每隔4个字节往前读取一个整数。
   }
 in_and_out.close();
  }
 catch(IOException e){System.out.println("??????");} 
 }
}



20-例子10
import  java.io.*;
class Example20_10 
{ public static void main(String args[])
 { try{
  RandomAccessFile file=new RandomAccessFile("Example20_10.java","rw");
  long filePoint=0;
  long fileLength=file.length();
  while(filePoint<fileLength)
  {String s=file.readLine();
   System.out.println(s);
   filePoint=file.getFilePointer();
   }
  file.close();
  }
  catch(Exception e){}
 }
}



20-例子11
import  java.io.*;
class Example20_11 
{ public static void main(String args[])
 { PipedOutputStream  out=null;
   PipedInputStream  in=null;
  try
   { out=new PipedOutputStream();
     in=new PipedInputStream();
     in.connect(out);