java io
- import java.io.*;
- public class TestIO{
- public static void main(String[] args) throws IOException{
- //1.以行为单位从一个文件读取数据
- BufferedReader in =new BufferedReader(new FileReader(\"F:
- epalonTestIO.java\"));
- String s, s2 = new String();
- while((s = in.readLine()) != null)
- s2 += s + "\\";
- in.close();
- //1b. 接收键盘的输入
- BufferedReader stdin =new BufferedReader(new InputStreamReader(System.in));
- System.out.println(\"Enter a line:\");
- System.out.println(stdin.readLine());
- //2. 从一个String对象中读取数据
- StringReader in2 = new StringReader(s2);
- int c;
- while((c = in2.read()) != -1)
- System.out.println((char)c);
- in2.close();
- //3. 从内存取出格式化输入
- try{
- DataInputStream in3 =new DataInputStream(new ByteArrayInputStream(s2.getBytes()));
- while(true)
- System.out.println((char)in3.readByte());
- }
- catch(EOFException e){
- System.out.println(\"End of stream\");
- }
- //4. 输出到文件
- try{
- BufferedReader in4 =new BufferedReader(new StringReader(s2)); //把s2当作输入对象
- PrintWriter out1 =new PrintWriter(new BufferedWriter(new FileWriter(\"F:epalon TestIO.out\")));
- int lineCount = 1;
- while((s = in4.readLine()) != null)
- out1.println(lineCount + \":\" + s);
- out1.close();
- in4.close();
- }
- catch(EOFException ex){
- System.out.println(\"End of stream\");
- }
- //5. 数据的存储和恢复
- try{
- DataOutputStream out2 = new DataOutputStream(new BufferedOutputStream(new FileOutputStream(\"F:epalon Data.txt\")));
- out2.writeDouble(3.1415926);
- out2.writeChars(" Thas was pi:writeChars ");
- out2.writeBytes( "Thas was pi:writeByte ");
- out2.close();
- DataInputStream in5 = new DataInputStream(new BufferedInputStream(new FileInputStream(\"F:epalon Data.txt\")));
- BufferedReader in5br = new BufferedReader(new InputStreamReader(in5));
- System.out.println(in5.readDouble());
- System.out.println(in5br.readLine());
- System.out.println(in5br.readLine());
- }
- catch(EOFException e){
- System.out.println(\"End of stream\");
- }
- //6. 通过RandomAccessFile操作文件
- RandomAccessFile rf = new RandomAccessFile(\"F:epalon rtest.dat\", \"rw\");
- for(int i=0; i<10; i++)
- rf.writeDouble(i*1.414);
- rf.close();
- rf = new RandomAccessFile(\"F:epalon rtest.dat\", \"r\");
- for(int i=0; i<10; i++)
- System.out.println(\"Value \" + i + \":\" + rf.readDouble());
- rf.close();
- rf = new RandomAccessFile(\"F:epalon rtest.dat\", \"rw\");
- rf.seek(5*8);
- rf.writeDouble(47.0001);
- rf.close();
- rf = new RandomAccessFile(\"F:epalon rtest.dat\", \"r\");
- for(int i=0; i<10; i++)
- System.out.println(\"Value \" + i + \":\" + rf.readDouble());
- rf.close();
- }
- }
关于代码的解释(以区为单位):
1区中,当读取文件时,先把文件内容读到缓存中,当调用in.readLine()时,再从缓存中以字符的方式读取数据(以下简称“缓存字节读取方式”)。
1b区中,由于想以缓存字节读取方式从标准IO(键盘)中读取数据,所以要先把标准IO(System.in)转换成字符导向的stream,再进行BufferedReader封装。
2区中,要以字符的形式从一个String对象中读取数据,所以要产生一个StringReader类型的stream。
4区中,对String对象s2读取数据时,先把对象中的数据存入缓存中,再从缓冲中进行读取;对TestIO.out文件进行操作时,先把格式化后的信息输出到缓存中,再把缓存中的信息输出到文件中。
5区中,对Data.txt文件进行输出时,是先把基本类型的数据输出屋缓存中,再把缓存中的数据输出到文件中;对文件进行读取操作时,先把文件中的数据读取到缓存中,再从缓存中以基本类型的形式进行读取。注意in5.readDouble()这一行。因为写入第一个writeDouble(),所以为了正确显示。也要以基本类型的形式进行读取。
6区是通过RandomAccessFile类对文件进行操作。